william bateson and reginald punnett experiment

During their analysis, the researchers realized that there was an excess in the number of parental phenotypes (purple-long and red-round) in the F 2 results. In particular, of the 2,132 F 2 plants, 1,199 were expected to have purple flowers and long pollen grains, but instead, there were a whopping 1,528 plants with this phenotype. Similarly, only 133 plants were expected to have red flowers and round pollen grains, but the researchers observed nearly three times that many (381). It is now understood that the differences between the expected and observed results were statistically significant (P 2 ] test can be used to statistically test for independent assortment of the phenotypes for flower color and pollen shape, as shown by the c 2 value in Table 1.)

Because the parental phenotypes reappeared more frequently than expected, the three researchers hypothesized that there was a coupling, or connection, between the parental alleles for flower color and pollen grain shape (Bateson et al. , 1905), and that this coupling resulted in the observed deviation from independent assortment. Indeed, Figure 1 shows an example of a cross between homozygous pea plants with purple flowers and long pollen grains and homozygous plants with red flowers and round pollen grains that exhibits linkage of the parental alleles.

But why are certain alleles linked? Bateson, Saunders, and Punnett weren't sure. In fact, it was not until the later work of geneticist Thomas Hunt Morgan that this coupling, or linkage, could be fully explained.

Morgan Finds Answers in the White-Eyed Fly

At the beginning of the twentieth century, Thomas Hunt Morgan's famous "fly room" at Columbia University was the site of many discoveries and "eureka" moments in the field of genetics. Morgan chose to use the prolific fruit fly Drosophila melanogaster as a model to study genetics. Then, for a period of three years, Morgan and his students struggled to find a way to create a fly that looked different from normal flies by treating these flies with heat, cold, X-rays, acids, bases, sugars, and other chemicals.

Finally, in 1910, Morgan fortuitously discovered a single fly with white eyes that did not result from any of his treatments. (Normal fruit flies have red eyes, not white eyes.) Morgan immediately crossed this white-eyed male fly to its red-eyed sisters (Morgan, 1910). Interestingly, when Morgan later inbred the heterozygous F 1 red-eyed flies, the traits of the F 2 progeny did not assort independently. Morgan expected a 1:1:1:1 ratio of red-eyed females, red-eyed males, white-eyed males, and white-eyed females. Instead, he observed the following phenotypes in his F 2 generation:

• 2,459 red-eyed females
• 1,011 red-eyed males
• 782 white-eyed males

There were no white-eyed females, and Morgan wondered whether this was because the trait was sex-limited and only expressed in male flies. To test whether this was indeed the case, Morgan completed a second cross between the original white-eyed male fly and some of his F 1 daughters. These crosses produced an F 2 generation with the following phenotypes:

• 129 red-eyed females
• 132 red-eyed males
• 88 white-eyed females
• 86 white-eyed males

Thus, the results of this cross did produce white-eyed females, and the groups had approximately equal numbers. Morgan therefore hypothesized that the eye-color trait was connected with the sex factor (Morgan, 1910). This in turn led to the idea of genetic linkage, which means that when two genes are closely associated on the same chromosome, they do not assort independently (Morgan, 1911).

Morgan's proposal was an early suggestion that genes were real, physical objects that were located on chromosomes (Robbins, 2000). Indeed, knowledge of genetic linkage was critical to prove that genes were actual objects that could be inherited, undergo recombination , and be mapped to specific locations on chromosomes. For instance, after Morgan's findings were published, Reginald C. Punnett used this information to identify linkage groups in his previous plant studies, and he associated these linkage groups with chromosomes (Punnett, 1923; Punnett, 1927). Also, with this knowledge in place, Morgan and Alfred H. Sturtevant , his student, conducted further studies of linkage that provided information regarding gene location on chromosomes and ultimately resulted in gene mapping .

Why Didn’t Mendel Observe Linkage?

Since the publication of Mendel's findings, other scientists have performed the pea plant crosses that could have shown linkage: i - a , v - fa , v - le , and fa - le . However, all of the pairs, except v - le , are so distantly located that Mendel would have been unable to detect linkage. In other words, although these pairs of genes are syntenic, they are not statistically linked. Therefore, they behave as though they independently assort. The v-le cross, on the other hand, would have shown linkage if Mendel had completed the cross. Possibly, with just one more cross, Mendel would have discovered linkage himself.

Thus, through their work with pea plants, Bateson, Saunders, and Punnett discovered an apparent exception to one of Mendel's foundational proposals: the principle of independent assortment . In particular, the trio suspected that certain alleles must somehow be linked to one another, thereby explaining why particular crosses yielded particular phenotypes in unusual numbers. A fuller explanation of this observation came only a few years later, when Thomas Hunt Morgan used fruit flies to show that linkage results when two genes are located near each other on the same chromosome. Since Morgan's time, this idea has served as the basis for continued research in the areas of gene mapping and recombination, to name but a few. Perhaps, if Mendel had carried out just one additional test cross with his plants back in the 1860s, he, rather than Bateson, Saunders, Punnett, and Morgan, would have been the one to uncover this fascinating area of study.

References and Recommended Reading

Bateson, W., et al . Experimental studies in the physiology of heredity. Reports to the Evolution Committee of the Royal Society 2 , 1–55, 80–99 (1905)

Blixt, S. Why didn’t Gregor Mendel find linkage? Nature 256 , 206 (1975) doi:10.1038/256206a0 ( link to article )

Bridges, C. B. Salivary chromosome maps with a key to the banding of the chromosomes of Drosophila melanogaster . Journal of Heredity 26 , 60 – 64 (1935)

———. A revised map of the salivary gland X-chromosome. Journal of Heredity 29 , 11 – 13 (1938)

Hillers, K., & Villeneuve, A. Chromosome-wide control of meiotic crossing over in C. elegans . Current Biology 13 , 1641–1647 (2003) doi:10.1016/j.cub.2003.08.026

Mendel, G. Experiments in plant hybridization. Trans. by William Bateson . (1866) ( link to article )

Morgan, T. H. (1910). Sex-limited inheritance in Drosophila . Science 132 , 120 – 122 (1910)

———. Random segregation versus coupling in Mendelian inheritance. Science 34 , 384 (1911)

Passarge, E., et al . Incorrect use of the term synteny. Nature Genetics 23 , 387 (1999) doi:10.1038/70486 ( link to article )

Pierce, B. Genetics: A Conceptual Approach ( New York, W. H. Freeman, 2005)

Punnett, R. C. Linkage in the sweet pea ( Lathyrus odoratus ). Journal of Genetics 13 , 101–123 (1923)

———. Linkage groups and chromosome number in Lathyrus . Proceedings of the Royal Society of London: Series B, Containing Papers of a Biological Character 102 , 236 – 238 (1927)

Robbins, R. J. Introduction to sex-limited inheritance in Drosophila , by T. H. Morgan (Electronic Scholarly Publishing, 2000) ( link to article )

Sturtevant, A. H. The linear arrangement of six sex-linked factors in Drosophila , as shown by their mode of association. Journal of Experimental Zoology , 14 , 43 – 59 (1913)

Weiner, J. Time, Love, Memory: A Great Biologist and His Quest for the Origins of Behavior ( New York, Random House, 1999)

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Reginald Punnett

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• DNA from the Beginning - Biography of Reginald Crundall Punnett
• Kirkwood Community College - Biography of Reginald Crundall Punnett

Reginald Punnett (born June 20, 1875, Tonbridge, Kent , England—died January 3, 1967, Bilbrook, Somerset) was an English geneticist who, with the English biologist William Bateson , discovered genetic linkage.

Educated at the University of Cambridge , Punnett began his professional research with structural studies of marine worms. Later his interest turned to genetics , and, while a demonstrator in zoology at Cambridge (1902–05), he joined a genetic study group under Bateson. Through his contact with Bateson, Punnett came to support the theories of Gregor Mendel , the founder of modern genetics . Subsequently, he wrote Mendelism (1905), the first textbook on the subject.

Using poultry and sweet peas, Punnett and Bateson discovered some of the fundamental processes of Mendelian genetics, including linkage, sex determination , sex linkage, and the first example of autosomal (nonsexual chromosome) linkage. In 1910 Bateson and Punnett founded the Journal of Genetics, which they jointly edited until Bateson’s death (1926). In 1912 Punnett became a fellow of the Royal Society of London and was named professor of genetics at Cambridge.

During World War I , when many foods were scarce, Punnett pointed out the value of employing sex-linked plumage-colour factors to distinguish male from female chickens; early identification of the less valuable males was thus made possible. The process, known as autosexing, is treated in his Heredity in Poultry (1923).

History of Knowledge

Research, Resources, and Perspectives

Punnett Squares and Hybrid Crosses: How Mendelians Learned Their Trade by the Book

In 1901, Erich von Tschermak (1871–1962) produced a critical edition of Gregor Mendel’s (1822–1884) paper on “Versuche über Pflanzen­hybriden”; and in the same year, William Bateson (1861–1926) submitted an English translation entitled “Experiments in Plant Hybridization” to the readers of the Journal of the Royal Horticultural Society . [1] Tschermak’s edition appeared as volume 121 of the renowned series Ostwalds Klassiker der exakten Natur­wissen­schaften (Ostwald’s Classic Texts in the Exact Sciences). Historians have rarely noted the paradox that lies in the fact that a paper, which scientists like von Tschermak and Bateson had lifted from obscurity just a year earlier, was almost instantaneously included in the Pantheon of classical contributions to the “exact” sciences. The discipline that Mendel supposedly founded, namely genetics, did not yet exist in 1901, and his alleged “discovery” of laws of inheritance would remain highly contested for at least another decade, even involving accusations of scientific misconduct. [2]

To resolve this paradox, it is important to note that Mendel’s paper did not only present a new theoretical perspective on the problem of inheritance. It also introduced a unique and highly counter-intuitive combination of mathematical and biological methods—in essence, methods of combinatorial analysis and artificial hybridization. [3] This raises the possibility that Mendel’s paper was not so much taken up by early Mendelians for its theoretical content but in order to acquire and rehearse the practical skills needed to carry out experiments. If we follow this historical interpretation, Mendel’s paper was read as a treatise in applied mathematics and experimental design, and its rapid reception among biologists would be better explained as the diffusion of a computational and experimental protocol.

In order to see if this interpretation was viable, we looked at Mendel’s paper itself in a fresh way and followed up its reception in some of the early textbooks and manuals that taught how the new science of genetics was supposed to be done and not necessarily how biological phenomena were supposed to be understood. How did these early genetics manuals present the subject? What kinds of difficulties did their readers encounter? How did graphs and diagrams contribute to understanding experimental and computational protocols? How engaged were the readers of these publications?

To answer these questions, we visited a variety of libraries and examined copies of introductions to Mendelian genetics published in the first quarter of the twentieth century. We found readers had annotated these books by underlining text sections; leaving various other reading marks such as lines connecting different parts of the text; inserting question or explanation marks; and adding comments, explanations, or criticisms to the margin of the pages. We examined copies of Tschermak’s edition of Mendel’s paper, R. C. Punnett’s Mendelism , W. Johannsen’s Elemente der exakten Erblichkeitslehre (Elements of an Exact Science of Heredity), W. Bateson’s Mendel’s Principles of Heredity , E. Baur’s Einführung in die experimentelle Vererbungslehre (Introduction to the Experimental Science of Heredity), W. E. Castle’s Genetics and Eugenics , and R. A. Fisher’s Statistical Methods for Research Workers . All these textbooks went through several editions and remained in use for decades, well into the second half of the twentieth century. Generations of researchers and students read and annotated them as they learned the trade of genetics by repeating the experiments and calculations printed in those books. Some of the copies we examined in Uppsala, Svalöf, Copenhagen, Berlin, and Woods Hole had distinguished owners. We traced books belonging to renowned geneticists such as Wilhelm Johannsen (1857–1927) and Herman Nilsson-Ehle (1873–1949). In other cases, however, we were unable to identify the readers who left marginal notes and other markings in these books. This was the case, for example, with the copies preserved at the Berlin State Library, where only the accession records, not the lending registers, are still available.

Placed one next to the other, the genetics manuals we examined appear at first glance as an uneven set. The slim second edition of Reginald Punnett’s (1875–1967) Mendelism , printed in octavo with less than one hundred pages makes a sharp contrast with the encyclopaedic Elemente , by Johannsen , a book of over five hundred pages with a trim size double the octavo. Punnett’s book was conceived as a short, accessible essay, as the author explained in the introduction. It could only give a taste of Mendelian genetics, whereas Johannsen’s was a complex treatise with detailed discussions of experimental and computational protocols related both to Mendel’s laws and to Johannsen’s pure line theory. In some cases, the same author produced more than one manual for different readerships. This was the case, for instance, with Erwin Baur (1875–1933), whose 1911 Einführung was followed ten years later by a new textbook prepared for farmers, gardeners, and forestry workers only half the size of the previous manual.

Despite the undeniable differences in their agendas and intended readerships, these manuals all contributed to the formation of a homogeneous visual language for genetics. Arrows, straight lines, and tree-like structures were used to depict experimental crossings on the page. The square diagram introduced by and now named after Punnett became a visual instrument for carrying out the combinatorial calculations that had been embedded in Mendel’s paper in textual and mathematical form. [4] Other authors of genetics manuals, for instance Bateson, quickly integrated this tool in their own textbooks because it effectively explained complex crossings to readers less at ease with computations. The analysis of variance method developed by the statistician and geneticist Ronald Fisher (1890–1962) was also a tool designed to facilitate statistical calculations: the experimental results were displayed in a table, and subdivided by classes according to their cause of variation. This tabular arrangement made the structure of the experiment clearer and the arithmetic simpler. [5]

Photographic plates and colour drawings were widely used in many early genetics manuals. Browsing the pages of Bateson’s , Baur’s and Castle’s manuals, for instance, even the modern reader appreciates the detail and elegance of their iconography. Plants and animals (peas, primulas, snapdragons, maize, butterflies, fowls, mice, rabbits, and more) together with their inheritance laws for color and other features are revealed to the reader. These lavish illustrations made it into foreign-language editions too. In the 1910 German translation of Punnett’s manual, for instance, the images and drawings are maintained, but with translated captions.

The rich iconography of these genetics manuals, however, could be a helpful learning tool only for the engaged reader who went from text to image, from image to computation, and from computation back to text to fully understand the crossings described. And we found clear indications of the readers’ engagement in the annotated copies we examined. For instance, readers carefully followed computations: they repeated them in the book margins and added values not explicitly calculated, but they also dutifully amended mistakes when they discovered them (Figure 1).

Some of the most striking and illuminating examples for the practical engagement of prominent readers with these texts come from Tschermak’s edition of Mendel’s paper. Until recently, the personal copy of Nilsson-Ehle was preserved in the library of the plant breeding station at Svalöf, Sweden, which now belongs to the private company Lantmännen. On it’s back flyleaf, Nilsson-Ehle tried in vain, and with clear signs of frustration, to derive the Mendelian ratios for a bihybrid cross, a problem any student of genetics would consider trivial today (Figure 2). As his research notes preserved in the library of the University of Lund show, he later achieved quite some mastery in deriving Mendelian ratios for complex crosses, making use of the Punnett square. [6] But even someone as mathematically adept as Johannsen needed to take recourse to auxiliary lines to follow the basic combinatorics involved in this problem (Figure 3). Auxiliary lines drawn between text and diagram in his personal copy of the third edition of Punnett’s Mendelism demonstrate that he also relied on this visual instrument to intuit complex crosses, in this case involving three genetic factors (Figure 4).

At the same time, neither Johannsen nor Nilsson-Ehle showed any interest in the “Concluding Remarks” of Mendel’s paper, in which he speculated about the mechanisms by which traits are inherited. This lack of engagement suggests that, for early twenty-first-century researchers, the really intriguing aspect of Mendel’s paper was how it could be used to figure out the combinatorial nature of hybridization experiments. Visual tools like the Punnett square played a key role in this process because the mathematical arguments Mendel employed were far from intuitive. They needed to be rehearsed again and again to become what is second nature for geneticists today.

Staffan Müller-Wille is Associate Professor of History and Philosophy of the Life Sciences at the University of Exeter, and Editor-in-Chief of the journal History and Philosophy of the Life Sciences . Giuditta Parolini is Postdoctoral Researcher ( wissenschaftliche Mitarbeiterin ) at the Technical University of Berlin.

• Gregor Mendel, Versuche über Pflanzenhybriden: Zwei Abhandlungen, 1865 und 1869 , ed. Erich Tschermak, Ostwald’s Klassiker der exakten Wissenschaften 121 (Leipzig: Wilhelm Engelmann, 1901), https://archive.org/details/versucheberpfla00tschgoog ( https://archive.org/details/versucheberpfla00tschgoog ); Gregor Mendel, “Experiments in Plant Hybridisation, with an introductory note by W. Bateson, M.A., F.R.S.,” Journal of the Royal Horticultural Society 26 (1901): 1–32, https://www.biodiversitylibrary.org/item/164047#page/8/mode/1up .  ↩
• Gregory Radick, “Beyond the ‘Mendel–Fisher Controversy,’” Science 350, no. 6257 (2015): 159–60, https://doi.org/10.1126/science.aab3846 .  ↩
• Hans-Jörg Rheinberger and Staffan Müller-Wille, The Gene: From Genetics to Postgenomics (Chicago: University of Chicago Press, 2017), chap. 3.  ↩
• Anthony W. F. Edwards, “Punnett’s Square,” Studies in History and Philosophy of Biological and Biomedical Sciences 43 (2012): 219–24, https://doi.org/10.1016/j.shpsc.2011.11.011 .  ↩
• Giuditta Parolini, “The Emergence of Modern Statistics in Agricultural Science: Analysis of Variance, Experimental Design and the Reshaping of Research at Rothamsted Experimental Station, 1919–1933,” Journal of the History of Biology 48 (2015): 301–35.  ↩
• Staffan Müller-Wille, “Early Mendelism and the Subversion of Taxonomy: Epistemological Obstacles as Institutions,” Studies in History and Philosophy of Biological and Biomedical Sciences 36 (2005): 465–87.  ↩

William Bateson and the Birth of Genetics

William Bateson drawing (1861-1923)

On August 8 1861 ,  English biologist William Bateson was born. Bateson was the first person to use the term genetics to describe the study of heredity , and the chief popularizer of the ideas of Gregor Mendel  [ 7 ] following their rediscovery in 1900 by Hugo de Vries and Carl Correns .

“The concept of evolution as proceeding through the gradual transformation of masses of individuals by the accumulation of impalpable changes is one that the study of genetics shows immediately to be false. Once for all, that burden so gratuitously undertaken in ignorance of generic physiology by the evolutionists of the last century may be cast into oblivion. For the facts of heredity and variation unite to prove that genetic variation is a phenomenon of individuals.” – William Bateson, Mendel’s Principles of Heredity (1913)

William Bateson – Early Years

William Bateson was born in Whitby on the Yorkshire coast, the son of William Henry Bateson, Master of St John’s College, Cambridge. He was educated at Rugby School and at St John’s College in Cambridge, where he graduated BA in 1883 with a first in natural sciences. He traveled to the United States in order to study embryology and investigate the development of Balanoglossus . This sparked his interest in vertebrate origins. Later on, Bateson became a fellow of St John’s. He further studied variation and heredity while traveling in western Central Asia.

Mechanisms of Biological Evolution

Bateson’s early works on the mechanisms of biological evolution were strongly influenced by Charles Darwin  [ 5 ] and Francis Galton [ 6 ]. In his first important work, he showed that some biological characteristics are not distributed continuously, with a normal distribution, but discontinuously. Bateson saw the persistence of two forms in one population as a challenge to the then current conceptions of the mechanism of heredity.

The Study of Variation

In 1894, William Bateson published the book “ Materials for the study of variation “. In it, he intended to show that biological variation exists both continuously, for some characters, and discontinuously for others. He coined the terms ‘ meristic ‘ and ‘ substantive ‘. Three years later, Bateson reported conceptual and methodological advances in his study of variation. He wrote about a series of breeding experiments performed by is pupil, Miss E.R. Saunders, using the alpine brassica   Biscutella laevigata in the Cambridge botanic gardens. They intercrossed hairy and smooth forms of identical plants experimentally and found out that they present “ the same appearance of discontinuity which the wild plants at the Tosa Falls do. This discontinuity is, therefore, the outward sign of the fact that in heredity the two characters of smoothness and hairiness do not completely blend, and the offspring do not regress to one mean form, but to two distinct forms ”. In Materials Bateson noted and named homeotic mutations, in which an expected body-part has been replaced by another. The animal mutations he studied included bees with legs instead of antennae; crayfish with extra oviducts; and in humans, polydactyly, extra ribs, and males with extra nipples. These mutations are in the homeobox genes which control the pattern of body formation during early embryonic development of animals.

Early Research in Genetics

When Bateson directed a genetics research group at Cambridge, which consisted mostly of women associated with Newnham College, Cambridge. They provided assistance for his research program at a time when Mendelism was not yet recognized as a legitimate field of study and carried out a series of breeding experiments in various plant and animal species. The results supported and extended Mendel’s laws of heredity.

The Rediscover of Mendel

At about this time, Hugo de Vries and Carl Erich Correns began similar plant-breeding experiments. But, unlike Bateson, they were familiar with the extensive plant breeding experiments of Gregor Mendel in the 1860s, and they did not cite Bateson’s work.[7] Critically, Bateson gave a lecture to the Royal Horticultural Society in July 1899, which was attended by Hugo de Vries, in which he described his investigations into discontinuous variation, his experimental crosses, and the significance of such studies for the understanding of Heredity. He urged his colleagues to conduct large-scale, well-designed and statistically analysed experiments of the sort that, although he did not know it, Mendel had already conducted, and which would be “rediscovered” by de Vries and Correns just six months later.

The Science of Genetics

It is assumed that William Bateson first suggested using the word ‘ genetics ‘ (from the Greek gennō , γεννώ; “ to give birth “) to describe the study of inheritance. He first used the term publicly at the Third International Conference on Plant Hybridization in London in 1906. William Bateson co-discovered genetic linkage with Reginald Punnett and Edith Saunders, and he and Punnett founded the Journal of Genetics in 1910. Bateson also coined the term ‘ epistasis ‘ to describe the genetic interaction of two independent loci.  In June 1894 Bateson was elected a  Fellow of the Royal Society  and won their  Darwin Medal  in 1904 and their  Royal Medal  in 1920.

William Bateson became director of the  John Innes Horticultural Institution  in 1910 and moved with his family to Merton Park in Surrey. He was director there until his sudden death  on February 8, 1923, at age 64.

References and Further Reading:

• [1]  Coining the Term “Genetics”
• [2]  William Bateson at Britannica Online
• [3]  William Bateson at the International Bateson Institute
• [4] William Bateson at Wikidata
• [5] Charles Darwin’s ‘On the Origin of Species’ , SciHi Blog
• [6]  Sir Francis Galton – Polymath , SciHi Blog
• [7]  Gregor Mendel and the Rules of Inheritance , SciHi blog
• [8]  Carl Correns and the Principles of Heredity , SciHi blog
• [9]  Works by or about William Bateson  at  Internet Archive
• [10]  William Bateson 1902.  Mendel’s Principles of Heredity, a defence ,   C. J. Clay and Sons.
• [11]  Adrian Bird,  Genetics, epigenetics and disease ,  The Royal Society  @ youtube
• [12]  Bateson, William (1894).   Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species . Macmillan.
• [13] Bateson, William (1908).   The Methods and Scope of Genetics . Cambridge University Press.
• [14]  Bateson, William (1913).   Problems of Genetics . Yale University Press.
• [15] Timeline of English Geneticists , via Wikidata and DBpedia

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Article Contents

Brief biography, punnett’s square, partial coupling (linkage), the reduplication hypothesis, the arthur balfour professorship of genetics, population genetics, acknowledgements, literature cited.

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Reginald Crundall Punnett: First Arthur Balfour Professor of Genetics, Cambridge, 1912

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A W F Edwards, Reginald Crundall Punnett: First Arthur Balfour Professor of Genetics, Cambridge, 1912, Genetics , Volume 192, Issue 1, 1 September 2012, Pages 3–13, https://doi.org/10.1534/genetics.112.143552

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R. C. Punnett, the codiscoverer of linkage with W. Bateson in 1904, had the good fortune to be invited to be the first Arthur Balfour Professor of Genetics at Cambridge University, United Kingdom, in 1912 when Bateson, for whom it had been intended, declined to leave his new appointment as first Director of the John Innes Horticultural Institute. We here celebrate the centenary of the first professorship dedicated to genetics, outlining Punnett’s career and his scientific contributions, with special reference to the discovery of “partial coupling” in the sweet pea (later “linkage”) and to the diagram known as Punnett’s square. His seeming reluctance as coauthor with Bateson to promote the reduplication hypothesis to explain the statistical evidence for linkage is stressed, as is his relationship with his successor as Arthur Balfour Professor, R. A. Fisher. The background to the establishment of the Professorship is also described.

THE centenary of the foundation of Cambridge University’s Professorship of Genetics in 1912 provides a timely occasion to recall the contributions of its first holder, Reginald Crundall Punnett (1875–1967; Figure 1 ). Overshadowed by his senior colleague William Bateson (1861–1926), for whom the Professorship had been intended, and his successor R. A. Fisher (1890–1962), Punnett played an important role in the early days of Mendelian genetics. He wrote the first genetics textbook Mendelism (Punnett 1905), collaborated in the discovery of partial coupling (linkage), asked G. H. Hardy the question that led to the formulation of what became known as Hardy–Weinberg equilibrium, published Mimicry in Butterflies (Punnett 1915) and Heredity in Poultry (Punnett 1923a), and pioneered the use of sex-linked markers for sexing poultry chicks. He founded the Journal of Genetics with Bateson in 1911 and edited it alone after Bateson’s death. He was the first Secretary and was later President of the Genetical Society of Great Britain. His name is immortalized in “Punnett’s square” ( Figure 2 ).

R. C. Punnett. Courtesy of the Master and Fellows of Gonville and Caius College, Cambridge.

Punnett’s square, from the Second Edition of Mendelism (Punnett 1907).

F. A. E. Crew (Crew 1967) wrote Punnett’s biographical memoir for the Royal Society, to which Punnett was elected in 1912, and followed this with a shorter account for GENETICS ( Crew 1968 ). In the opening paragraph of the latter he said that Punnett “had the good fortune to be an active participant in the work that confirmed and extended the findings of Gregor Mendel when these were brought to light in 1900. He lived, therefore, in a period that was filled with excitement and could rightly feel that he was involved in a great adventure that would surely lead to a revolution in biological thought.” Crew’s memoirs should be consulted for details of Punnett’s life; here I concentrate on his scientific contributions and give only a brief biographical summary.

Punnett was born to George and Emily Punnett (née Crundall) at Tonbridge, Kent, on June 20, 1875. Both parents were of Kentish stock. He was educated at Clifton School, Bristol, and Gonville and Caius College, Cambridge, which he entered as a scholar in 1895. Originally registering as a medical student, he took the Natural Sciences Tripos, specializing in zoology in his third year and being placed in the first class in the Tripos in 1898. He spent the next year at the Naples Zoological Station (Naples, Italy) and at Heidelberg University (Heidelberg, Germany) and in September 1899 accepted the post of Demonstrator in the Natural History Department of the University of St. Andrews (St. Andrews, Fife, Scotland). In October 1901 a Fellowship of Gonville and Caius College followed, capped by the University post of Demonstrator in Morphology, which he held until 1904, when he became Balfour Student in Zoology. This studentship, in memory of Francis Balfour, Professor of Animal Morphology, Arthur Balfour’s brother, had been held by William Bateson from 1897 to 1900.

Then in 1908 Punnett started a rapid rise up the academic ladder. Still with his Caius Fellowship (which he was to retain until his death) he became Demonstrator in Animal Morphology in the Department of Zoology, Superintendent of the Museum of Zoology in 1909, and, when Bateson resigned his Professorship of Biology in 1910 to take up the Directorship of the John Innes Institute, Punnett succeeded to it. In 1912 the Arthur Balfour Professorship of Genetics was founded and, following the failure of the University to attract Bateson back from his Directorship, Punnett was appointed. We consider the history of the Professorship in a later section.

At Naples in 1899 Punnett started to study the morphology of nemertine (or “Nemertean”) marine worms, and these continued to be his main interest at St. Andrews and on his return to Cambridge. In 1903 he embarked on a statistical study “On nutrition and sex-determination in man,” using data for London from the 1901 Census, which revealed a modest facility in handling numbers ( Punnett 1903 ). The human sex ratio was my own Ph.D. topic and in 1959 I must have heard about his interest and sent him an offprint of one of my articles ( Edwards 1958 ) for I still have his letter in reply.

Punnett’s association with Bateson started at the beginning of 1904. Some time earlier, “Knowing that Bateson was carrying out Mendelian experiments at Merton House, Grantchester, [Punnett] wrote to him suggesting that perhaps his nutritional experiments might be so designed that they would yield information concerning the inheritance of coat colour [in the mouse]” ( Crew 1967 ). When Bateson received an offer of financial support from his friend Mrs. Christiana Herringham in December 1903, he first thought of Leonard Doncaster as an associate, but Doncaster declined ( Cock and Forsdyke 2008 , p. 217) and so he wrote to Punnett (on Christmas Day), inviting him to come “into partnership in my breeding experiments.” “Mr. Punnett joined with enthusiasm, and very generously refused the ... salary” ( Bateson 1928 , p. 87), “... and so a partnership that was to last six years and that was to make notable and enduring contributions to genetics came into being. The two men were very different temperamentally, Bateson was a forceful personality, combative and stern; Punnett was retiring, tolerant and friendly; it was a happy and harmonious partnership” ( Crew 1967 ).

In 1913 Punnett married Eveline Maude Froude, widow of Sidney Nutcombe-Quicke. They lived in Whittingehame Lodge, Storey’s Way, Cambridge, in the house provided for the Arthur Balfour Professor, until Punnett retired in 1940 at the age of 65. He and his wife then moved to Bilbrook, near Minehead, Somerset, where he died on January 3, 1967. There were no children.

Crew’s (1967) biographical memoir contains a list of Punnett’s publications and summaries of his work beyond the topics I discuss in detail here. In the summer of 1909 Punnett had visited Ceylon to study mimetic butterflies, where he met his Caius colleague R. H. Lock, then Assistant Director of the Royal Botanical Gardens at Peradeniya (Sri Lanka). The visit led to a handsomely illustrated book Mimicry in Butterflies (Punnett 1915). “... it included a mutationist’s explanation for the evolution of complex mimetic resemblances between members of unrelated species” ( Bennett 1983 , p. 8). R. A. Fisher’s view of their evolution was completely different. He set it out in Fisher (1927) and in Chapter VIII, “Mimicry,” of The Genetical Theory of Natural Selection (Fisher 1930a) with special reference to Punnett’s view in the section “The theory of saltations.” Provine (1971, p. 150) gives an account. On evolution Fisher and Punnett were to cross swords again when Punnett reviewed The Genetical Theory , which we refer to below under Population Genetics .

Punnett’s experience with studying Mendelian characters in poultry led him to invent the method of using sex-linked plumage color factors to sex day-old chicks, thus enabling the unwanted majority of cockerels to be disposed of immediately. By 1940 he had published, alone or jointly, 11 “Genetic studies in poultry,” with another two to come in retirement in 1948 and 1957. Crew (1968) may be referred to for further details, for unlike the biographical memoir for the Royal Society his memoir in GENETICS contains a substantial extract by Professor F. B. Hutt “whose Genetics of the Fowl is in the direct line of Punnett’s Heredity in Poultry , 1923a” ( Crew 1968 ).

Punnett (1928) edited Bateson’s scientific articles for Cambridge University Press. T. H. Morgan (1929) reviewed the two volumes in Nature , regretting the omission of the Reports to the Evolution Committee (see below), which were represented only by summaries. After Bateson’s death in 1926, Punnett (1926) wrote a memoir of him in the Edinburgh Review , part of which was reprinted in Notes and Records of the Royal Society in 1952 (Punnett 1952).

he work for which Punnett is best remembered, the discovery of linkage jointly with William Bateson, arose out of their studies of Mendelian ratios in the sweet pea Lathyrus odoratus . The discovery is more properly referred to as “partial coupling” because the word “linkage” had not yet been coined in this connection, nor had its chromosomal basis been postulated. The analysis of the various ratios that characterized Mendelian inheritance was much facilitated by Punnett’s simple square diagram showing how gametes combine to make zygotes or sometimes how genotypes at two loci combine to make zygotes. Punnett’s square seems to have been a development of 1905, too late for the first edition of his Mendelism (May 1905) but much in evidence in Report III to the Evolution Committee of the Royal Society [( Bateson et al. 1906b ) “received March 16, 1906”]. The earliest mention is contained in a letter to Bateson from Francis Galton dated October 1, 1905 ( Edwards 2012 ). We have the testimony of Bateson (1909 , p. 57) that “For the introduction of this system [the ‘graphic method’], which greatly simplifies difficult cases, I am indebted to Mr. Punnett.” As we shall see, 1905 was also an important year in the discovery of partial coupling, so the two developments went hand in hand. Here we give the salient features of Punnett’s square, relying on the extended account by Edwards (2012) , which is fully illustrated.

The first published diagrams appeared in 1906. On February 1 Bateson, in an address to the Neurological Society (Bateson 1906), displayed the 9:3:3:1 Mendelian ratio among the F 2 for two loci when dominance is complete at both. Then Report III contained several, notably the ones on p. 3 (our Figure 3 ) and p. 10. Figure 3 displays the 9:7 ratio obtained when, to quote the figure legend, “The character, colour for example, appears only when C and R meet.” We consider the more complex figure on p. 10 in a moment. Figure 3 was repeated by Lock (1906 , p. 199) in his book Recent Progress in the Study of Variation , Heredity , and Evolution , the Preface being dated October 23. It will be noted that these squares are formed by the simple process of laying out the four gametotypes CR, cR, Cr, cr as headings for both rows (paternal gametes, say) and columns (maternal gametes) and “adding” them to create the entries in the squares corresponding to the zygotes formed by their unions.

Punnett’s square, from Report III (Bateson et al. 1906b).

However, when Punnett published the second edition of his Mendelism , he used a slightly different format (our Figure 2 ; Punnett 1907, p. 45) also displaying 9:3:3:1. It is divided into four large squares each of which contains four small squares. Each large square is identical in respect to the second locus, B,b, and shows the two types of gamete uniting to form zygotes, two of which, Bb and bB, are identical if gametic origin is ignored. The four large squares do the same for the first locus A,a, and then the four small squares for B,b are added to each of the large squares for A,a. Of course it comes to the same thing as Figure 3 , the difference being only a matter of the labeling. In the third edition (Punnett 1911, p. 34) he reverted to the arrangement of Figure 3 complete with a description of the construction of what he called the “chessboard” method (although in truth it is more like a multiplication table).

When three loci are involved, an 8 × 8 square results, as given in Report III on p. 10 ( Figure 4 ). This is an extremely interesting construction. Thinking of it as four large squares, we see that in respect to B,b and R,r, each of these squares is the same, but different from either of the methods of constructing a two-locus table so far described (in fact there is an error in columns 7 and 8, where the lower entries in row 5 have been interchanged). Instead of the union of gametes we have the union of loci, the rows for R,r, and the columns for B,b. Then each of these squares has been dropped into a square for C,c as in Punnett’s (1907) construction ( Figure 2 ). This hybrid format was suggested by Sir Francis Galton in a letter to Bateson dated October 1, 1905 containing the original of Figure 4 (reproduced in Edwards 2012 ). It is odd that when it was published, in Report III and later, Galton’s help was not acknowledged.

Galton’s three-locus square from Report III (Bateson et al. 1906b).

To appreciate the significance of Galton’s arrangement it is necessary to describe the situation that confronted Bateson and Punnett, and since the experiments involved are the very ones that led to the discovery of partial coupling, this serves as an introduction to the next section. “The work was begun,” wrote Bateson in his book Mendel’s Principles of Heredity ( Bateson 1909 , p. 89), “by crossing two white sweet peas belonging to the variety Emily Henderson. These plants were alike in every respect so far as could be perceived, excepting that the shapes of the pollen grains differed, the one having the normal long pollen grains of the species, while the other had roundish grains. The object of the experiment was to trace the descent of the pollen-character and at the beginning no question of colour was entertained. When F 1 was grown however it was clear that here was a remarkable opportunity of studying a reversion in color due to crossing, for these plants instead of being white were purple like the wild Sicilian plant from which our cultivated sweet peas are descended.”

Proceeding to the F 2 , Bateson and Punnett found “phenomena [which] … presented superficially an appearance of great complexity. … It is unnecessary to go through the long series of steps by which the analysis of the phenomena was carried out. The meaning of the facts is now perfectly clear and they can all be arranged in one consistent scheme” (Bateson 1909, p. 90). They worked out that three loci would do. The two original whites were CCrrBB and ccRRbb, leading to F 1 all CcRrBb. On selfing, these would lead to the 64 combinations shown in Figure 4 . In the presence of C (for color?) the situation is always that R (red) dominant to r gives a red flower to which B (blue) dominant to b adds blue to make a purple flower, although in the absence of R there is no blue alone. This is then the pattern in the three large squares corresponding to CC, Cc, and cC. In the fourth, cc, no colors of any kind appear. We end up with 3 × 9 = 27 purples, 3 × 3 = 9 reds, and 3 × 4 + 16 = 28 whites. The numbers given in Report III are 1634, 498, and 1593, respectively, 3725 in all, against expectations of 1571, 524, and 1630 ( χ 2 on 2 d.f. = 4.59, P = 0.10; all values of χ 2 quoted here are newly calculated).

It is frequently said that linkage was discovered by Bateson and Punnett in 1905. Thus A. H. Sturtevant himself, writing A History of Genetics in retirement (Sturtevant 1965), records (p. 40) that “Incomplete linkage was first reported in the sweet pea by Bateson and Punnett (1905) ,” but already some qualifications are needed. First, “in the sweet pea” needs to be in parentheses, or at least between commas, because this was the first report of partial linkage in any organism. Second, the reference is actually to Bateson et al. (1905) , as given by Sturtevant in his bibliography, which raises the question of the contribution of Saunders. ( Morgan 1928 , in The Theory of the Gene , p. 323, went further and omitted Saunders from the reference too.) Third, the word linkage in its genetical context had not, in 1905, been coined and is associated with the chromosomal theory advanced by Morgan (1911) , who even then still used the term “coupling.” The first use of linkage in this connection is in 1912 (Morgan and Lynch 1912), but we should note that Bateson (1906) had written “We have proof that in certain cases a character, say of shape, may be so linked or coupled with another character, say of color, that all or a majority of the germs [gametes] which carry the one carry the other also.” Punnett (1911, p. 87), in the third edition of his Mendelism , wrote “In some way or other the factors for blue and for long pollen become linked together in the cell divisions that give rise to the gametes, but the linking is not complete.”

In the present account I use coupling for the statistical evidence as opposed to its chromosomal explanation, and, like Bateson and Punnett, I distinguish between complete coupling and partial coupling. This distinction is important, because complete coupling had already been found by Correns (1900) in stocks ( Matthiola ) as noted by Bateson and Saunders (1902) , who reported similar “correlation” in their own experiments with stocks. Correns had used the word “gekoppelte.” Although this 1902 Report to the Evolution Committee of the Royal Society ( Bateson and Saunders 1902 ) was the joint work of Bateson and E. Rebecca Saunders (“Becky”), Part I, in which the correlation was noted, is headed “Experiments with Plants, carried out by E. R. Saunders,” to whom therefore we may attribute the observation.

Partial coupling appears for the first time in Report II to the Evolution Committee ( Bateson et al. 1905 ; received May 18, 1904), the one to which Sturtevant referred. It contains no further reference to correlation in its Matthiola section, but in the section on sweet peas we read “ There is , therefore , some coupling of pollen-shape and colors ” (italics original) ( Bateson et al. 1905 , p. 89). This section is headed “Experiments carried out by W. Bateson, E. R. Saunders, and R. C. Punnett (in 1904).” It is evident that many additions to Report II were made after May 1904, including a “Note added December 1904” at the end. The earliest mention of disturbed segregations corresponding to this coupling is in Bateson’s Report to the Committee on Experimental Studies in the Physiology of Heredity at the British Association meeting in Cambridge in August 1904 (Bateson 1905) and his Presidential Address to the Zoological Section at the meeting (also reproduced in Bateson 1928 ; the mention is on p. 255).

Then in Report III ( Bateson et al. 1906b ; received March 16, 1906) there is a full section on “Gametic Coupling,” which starts “Early in the revival of breeding experiments, attention was called, especially by Correns, to the phenomenon of coupling between characters. .... Examples of partial coupling have not hitherto been adequately studied. A remarkable case occurs in regard to the distribution of the pollen-characters in F 2 from the white long x white round Sweet Pea” ( Bateson et al. 1906b , p. 9), and the results are printed. More information is given in the later section of Report III devoted to the sweet pea itself (“Experiments by W. Bateson, E. R. Saunders and R. C. Punnett”). The crucial results had in fact appeared earlier in a brief note in Proceedings of the Royal Society , Series B ( Bateson et al. 1906a ; received December 1 and read December 7, 1905).

Finally, Report IV ( Bateson et al. 1908 ) contains, in its introduction, a brief review of work on partial coupling, which starts “The majority of our Sweet Pea work of the past two seasons was undertaken with a view to further elucidating the phenomenon we have termed gametic coupling” ( Bateson et al. 1908 , p. 2). The section on sweet peas is headed “Experiments by W. Bateson and R. C. Punnett” and contains a subsection “Partial Gametic Coupling.”

There is some slight evidence that Sturtevant, in his History , might knowingly have credited this discovery of partial coupling to Bateson and Punnett, omitting Saunders. Although Saunders was the undoubted Queen of Matthiola , Punnett does seem to have been King of L. odoratus . Sturtevant (1965, Author’s Preface, p. xi) had “some direct personal contact” with Bateson and Punnett and had met Saunders, although she counted among those he “never really knew.” Bateson (1906), when discussing color in the sweet pea, refers to “an elaborate series of experiments made by Miss Saunders, Mr. Punnett, and myself,” but in the corresponding part of his book Mendel’s Principles of Heredity (Bateson 1909, p. 89) he refers to experiments as having been “carried on jointly by Mr. Punnett and myself for some years.” Nor is there any sense that he is inclined to neglect Saunders’ work, for the next section (Bateson 1909, p. 95) on “Colors of Stocks” ( Matthiola ) starts “The experiments of Miss E. R. Saunders have revealed ... .” For further information about Saunders see Richmond (2001 , 2006 ) and references therein. Lock (1906 , p. 200), a member of Bateson’s group at the time, says firmly “This phenomenon of partial gametic coupling was discovered by Bateson and Punnett in the Sweet Pea.” Punnett (1914) himself was characteristically self-effacing: “Bateson in 1905 was the first to describe in sweet-peas a remarkable case in which two characters each exhibiting ordinary Mendelian segregation nevertheless showed a peculiar distribution with regard to one another.” Report II refers to “the original crosses of 1901.” Punnett joined the sweet-pea work in 1904, growing the F 2 in which he and Bateson noted the disturbed segregations, so the F 1 must have been 1903, which would make the original cross 1902. Perhaps there were some in both 1901 and 1902.

In his reminiscences “Early days of genetics” given at the hundredth meeting of the Genetical Society at Cambridge in 1949, Punnett (1950) said “Sweet peas were the other main line of inquiry. We grew some thousands each year and of course the garden at Merton House [the Bateson home in Grantchester] could not nearly accommodate such numbers.” He goes on to describe the additional plots on the University Farm at Impington, four miles away, and the ride there “for a long afternoon, Bateson with his wife in the trailer carrying the ‘Farm Book’ and a microscope.” “One of us pulled the plant and sung out its characters and handed the plant to the other, who, with the microscope perched on some odd box picked up at the farm, determined the shape of the pollen. All duly logged by Mrs. Bateson” (Punnett 1950).

The “Farm Books” and allied notebooks recording experimental data are preserved in Cambridge University Library and might provide further information about the participants, if only by the handwriting. But no doubt they all helped each other, and it looks as though Mrs. Bateson deserved a formal mention too.

Bateson and Punnett found an F 2 segregation 2844 long pollen and 881 round, against 3:1 expectations of 2794 and 931, respectively ( χ 2 on 1 d.f. = 3.62, P = 0.057). As we have seen, in the field they scored the color before the pollen type so it would be natural to have three columns for the colors, each divided into two for the pollen type, and this is how the data were presented in Report III ( Table 1 ). They noted that the 3:1 ratio did not hold for the three color types individually. There seemed to be some kind of coupling of round with red and long with purple that was disturbing the Mendelian segregations; white seemed to be unaffected. Bateson and Punnett’s explanation was that B (blue) and L (for long) tended to associate in the gametes, as did their recessive counterparts b and l (round). The converse to this coupling was the “repulsion” of B and l , b and L .

F 2 segregation in the sweet pea for flower color and pollen type

Alas, it did not occur to Bateson and Punnett that the “several processes” they could contemplate for the explanation of partial coupling need not be limited to integral values of n , and they became fixated on the further idea that n had to be a power of 2 [“pure numerology brought about by a fixation on Mendelian ratios” ( Edwards 1996 )], for they began to visualize processes of gametogenesis that required this as an explanation, their so-called “reduplication” hypothesis ( Bateson and Punnett 1911 ; see below). If they had kept an open mind and allowed any value of n , or better still worked with the simpler θ , they would have been free to choose the best value without restriction. As late as March 1911, the date of the Preface to his third edition of Mendelism , Punnett writes (Punnett 1911, p. 87) “Nor for the present can we suggest why certain factors should be linked together in the peculiar way that we have reason to suppose that they are during the process of the formation of the gametes.”

Weldon (1902) had already applied Karl Pearson’s goodness-of-fit test to Mendel’s data, so that Bateson and Punnett could have chosen the value that gave the best fit by the criterion of χ 2 , thereby inventing the method of minimum χ 2 nearly a decade before Engledow and Yule (1914) did so (reprinted with a commentary by Edwards 1997 ). But that would have been stealing the biometricians’ clothes.

We conclude by noting that Punnett made a very prescient remark about partial coupling when addressing the Epidemiological Section of the Royal Society of Medicine on February 28, 1908, 3 years before Morgan’s chromosomal linkage theory. “Enough, however, is known to make it certain that it [partial coupling] often plays an important part in heredity, and I have laid some stress upon it because it may eventually be found to throw light upon the alleged association of certain physical peculiarities in man with particular forms of disease” ( Punnett 1908 ). The comment foreshadows the suggestion by Fisher (1935) in “Linkage studies and the prognosis of hereditary ailments” read to the International Congress on Life Assurance Medicine (see Edwards 2004 , for Haldane’s possible contribution), which in turn foreshadowed the similar suggestion by J. H. Edwards ( Edwards 1956) in connection with detecting marker loci in amniotic cells. For if a disease gene is linked closely enough to a marker locus, knowledge of the marker genotype may help in the prognosis of a disease not yet manifest. Punnett also remarked, in 1907 ( Mendelism ; Punnett 1907, p. 64), that “there is every probability that, as it [partial coupling] becomes better known, it will be found of peculiar importance in the elucidation of the architecture of the gamete.” In his last edition (Punnett 1927, p. 135) he reminded us of this by quoting it, adding “How brilliantly this prediction has been fulfilled by Professor Morgan and his colleagues will appear in the following chapter [the chromosome theory].”

For many years neither Bateson nor Punnett accepted the chromosomal explanation of linkage, and by “coupling” and “repulsion” they meant statistical associations as observed in the sweet pea. In a talk in 1959 Punnett said “I have sometimes been asked how it was that having got so far we managed to miss the tie-up of linkage phenomena with the chromosomes. The answer is Boveri. We were deeply impressed by his paper ‘On the Individuality of the Chromosomes’ and felt that any tampering with them by way of breakage and recombination was forbidden” ( Punnett 1950 ). In 1911 they advanced their “reduplication” hypothesis to explain coupling and its mirror phenomenon, repulsion. Its origin can be seen in some comments by Bateson in Mendel’s Principles of Heredity (1909, pp.157–161), but the definitive account is in Bateson and Punnett (1911) . By the time Whitehouse (1965) wrote his magisterial Toward an Understanding of the Mechanism of Heredity it had been forgotten. We use Sturtevant’s (1965) historical account:

According to the reduplication hypothesis, segregation does not occur at the time of meiosis but somewhat earlier, and not necessarily at the same time for each pair of genes. The cells that are finally produced, each with a single set of genes, then multiply at different rates to give the observed ratios. It is not easy to see why this scheme was developed, since there is nothing in it that seems related to the (2 n –1):1 series, nor is there any independent evidence for the complex and symmetrical pattern of divisions that it requires. The hypothesis is related to Bateson’s reluctance to believe that segregation occurs at the meiotic divisions (Sturtevant 1965, p. 40).

Sturtevant continues with further comments on Bateson’s thinking. For more information about the hypothesis and Bateson’s reluctance to accept the chromosome theory see Cock (1983) , who, interestingly, headed his section on it “Bateson’s own rival theory,” and Cock and Forsdyke (2008) . The best that can be said for the theory is that it seems to have spurred Morgan on to have his eureka moment in 1911 with the chromosomal explanation of linkage.

Punnett himself never incorporated reduplication into the later editions of his Mendelism , limiting his discussion to observations on the numerical ratios thought to be occurring. He pursued the question with further experiments in sweet peas ( Punnett 1913 , 1917a ), but by the second of these articles he was already considering Morgan’s explanation of linkage, and in the fifth edition of Mendelism (Punnett 1919, p. 133) he introduced a new chapter, “The Chromosome Theory” “to present the position of the supporters of the chromosome theory ... [which] is, at the present moment, the most keenly discussed question in heredity.” But the controversy was not really being discussed any more, and one senses that his heart was not in reduplication and he simply did not want to upset Bateson.

Bateson (1922) famously abandoned his doubts “after a week in close communion with the wonders of Columbia University” visiting Morgan’s laboratory. The observations of the Belgian cytologist F. A. Janssens published in 1909 had persuaded Morgan and most other people of the existence of crossing-over sufficient to account for the observed linkage phenomena, even though doubt remained about Janssens’ precise model (see the Perspectives by Koszul et al. , 2012, in GENETICS , Vol. 191, Num. 2). Morgan was to write, in The Theory of the Gene (Morgan 1928, p. 41) “From the nature of the case it is practically impossible to demonstrate, even when twisting of the chromosomes is admitted, that it actually leads to an interchange of the kind demanded by the genetic evidence.”

What did Punnett really think? According to Cock (1983) “At no time did Punnett show any great interest in chromosomes,” and I suspect that Punnett, who possessed “a blithe, kindly, open-air personality” ( Needham 1967 ) quite unlike the combative Bateson, might simply have opted for a quiet life. Cock (1983) continued “He is unlikely, therefore, to have given Bateson any stimulus toward a more favorable view of chromosome theory.” There is also the possibility that he was sensitive to the view of his friend Lock, who had suggested as early as 1906 (Lock 1906, p. 252) that coupling might be due to “some mechanism which causes the representative particles of the respective characters concerned to remain in company during the process by which the other allelomorphs are being reassorted between the chromosomes,” as had been noted by Morgan and his colleagues (Sturtevant 1965). Even when describing the zygotic ratios arising from gametic coupling in his 1919 edition of Mendelism , Punnett (1919, p. 124) does not describe the reduplication hypothesis, merely saying “More recently the term ‘reduplication’ has been brought into use. …. The term is not altogether satisfactory, for biologists are not at present in agreement as to the manner in which these gametic series come to be formed.” Torn between Bateson and Lock, it would have been charactistic of Punnett to have kept his head down, and in any case from 1911 Bateson was at the John Innes Institute and not in Cambridge.

The prehistory of the Arthur Balfour Professorship starts not with Punnett, but with Bateson, whom the University made a Reader in 1908. In their Report the recommending body, the General Board, had said that “they regret that in view of the state of University finances they cannot propose at the present time to establish a Professorship in Heredity and Variation” ( Cambridge University Reporter 1907–1908, p. 213). The academic and political background to this appointment is fully described by Cock and Forsdyke (2008, p. 303). Evidently wheels were turning behind the scenes, for on February 24, 1908 the University’s Council was able to publish a report “on a proposed Professorship of Biology” ( Cambridge University Reporter 1907–1908, p. 632; reprinted in part in Cock and Forsdyke, p. 306). An anonymous benefactor, likely to have been Arthur Balfour, had offered to support in part a Professorship to be devoted to “that branch of Biology now entitled Genetics (Heredity and Variation)” for 5 years in connection with the celebration of the Darwin centenary in 1909. Indeed, he wanted it to be the “Darwin Professorship,” but the Council thought a title should wait until “the professorship can … be placed on a permanent footing.” The duty of the Professor was quite specific: “to promote by teaching and research the knowledge of Genetics.” It was less than 3 years since Bateson had coined the word. The Professorship was clearly intended for him, and his election was announced on June 8. He gave his Inaugural Lecture “The Methods and Scope of Genetics” on October 23 (Bateson 1908) and it is from 1908 that Cambridge’s Professorship of Genetics really dates. For Punnett the “musical chairs” of posts led to the changes already mentioned in the biographical section above, culminating in his election to this Professorship of Biology when Bateson resigned it to take up the Directorship of the new John Innes Horticultural Institute in 1910.

Arthur James Balfour (1848–1930) was Prime Minister from 1902 to 1905, a brilliant aristocratic intellectual who held a key position in the Conservative party for nearly fifty years. He was the elder brother of Francis Balfour, who had lost his life in a climbing accident in 1882 soon after becoming Cambridge’s Professor of Animal Morphology. He had taught the undergraduate Bateson. Arthur Balfour’s many connections included his brother-in-law Lord Rayleigh, Chancellor of the University at the time of the Darwin Centenary, an office to which he himself succeeded in 1919. He was President of the British Association at the time of the 1904 Cambridge meeting and the foundation President of the Genetical Society in 1919, being succeeded on his death by Punnett. Among his undergraduate friends he counted George Darwin, with whom he played real (“court”) tennis, and George had taken him to visit his father Charles Darwin at his house in Downe, Kent. “The kindness of the great man, his sympathy and charm, exceeded all that could be demanded by the most self-centered guest, and left a deep impression on my youthful mind” ( Balfour 1930 , p. 38). Bateson could not have had a more powerful friend at court than Arthur Balfour.

During the 1909 Cambridge Darwin celebrations Balfour was chosen to propose Darwin’s “immortal memory” at the banquet on June 23. That morning the Chancellor, Lord Rayleigh, had ended his address of welcome to the delegates by saying

During the last generation, Cambridge, especially since the time of Michael Foster, has been active in biological work. We have the men and the ideas, but the difficulty has always been lack of funds. At the present time it is desired, among other things, to establish a Chair of Genetics – a subject closely associated with the name of Darwin and of his relative Francis Galton, and of the greatest possible importance, whether it be regarded from the purely scientific or from the practical side. I should like to think that the interest aroused by this Celebration would have a practical outcome in better provision for the future cultivation, in his own University and that of his sons of the field wherein Darwin labored ( Cambridge University Reporter 1908–1909, p. 1372).

The plea did not fall on deaf ears. In July 1910 Balfour wrote a short article dealing with the endowment of the study of Genetics in the University. Late in 1911 a meeting was held at Balfour’s house in London, as a result of which an anonymous benefactor placed in the hands of Balfour’s friend Viscount Esher the sum of £20,000 to endow a Professorship to be called the Balfour Professorship of Genetics ( Cambridge University Reporter 1911–1912, p. 694). Regulations were drawn up, which stipulated that the initial appointment should be made by Balfour and the Prime Minister jointly. It was also decided that the title should be the Arthur Balfour Professorship to avoid confusion with Francis Balfour.

Balfour wrote to Bateson, inviting him to accept the Professorship, but Bateson, unwilling to return from his Directorship of the John Innes Institute, declined and suggested that Punnett “is in every way worthy to be appointed” (Cock and Forsdyke 2008, p.386). And so he was, on November 11, 1912, being formally admitted at the Congregation on November 22. Whittingehame Lodge, the Professor’s house, was presented to the University in 1914 by Viscount Esher and Arthur Balfour, by then an Earl.

Punnett’s legacy to Cambridge University as Professor was modest. When his successor R. A. Fisher was elected in 1943, he found no staff and no students, but the large house, Whittingehame Lodge, intended for his occupation. “With the coming of war, the house was let to tenants and the land plowed up by the War Agricultural Committee. The department ceased to exist” ( Box 1978 , p. 398). Fisher was able to live in Caius College, since his Fellowship had been renewed on his return to Cambridge. Between 1943 and his retirement in 1957 he used the house and garden to develop a small Department and start a third-year Natural Sciences Tripos subject, “Genetics.” Nowadays the Department thrives, and one valuable direct legacy of Punnett’s remains to this day: his collection of offprints and many of his books.

However, Punnett influenced the young Fisher, who was a student in Caius College in 1909–1913 during which time he helped to found the Cambridge University Eugenics Society, approaching Punnett, one of the dons who was a member of the national Society, to serve on its Council. Punnett gave a lecture at the second public meeting of the University Society on December 5, 1911. “The undergraduate committee of the Society found Punnett’s exposition of Mendelism so important that, at a meeting in Fisher’s rooms [in Caius] the following term, Fisher as chairman proposed that they should make it a rule that each academic year one paper be devoted to an elementary exposition of the principles of heredity, meaning, of course, Mendelism” ( Mazumdar 1992 , p. 99).

From 1920 to 1926 Fisher was a Fellow of Caius at the same time as Punnett and though not resident he would have met him frequently. It was Punnett who, with Karl Pearson, reported unfavorably for the Royal Society on Fisher’s (1918) famous article “The correlation between relatives on the supposition of Mendelian inheritance,” prompting Fisher to remark to W. F. Bodmer in 1956 “My 1918 paper was refereed by Pearson and Punnett, both of whom I later succeeded” [personal communication; see also Fisher's letter to C. S. Stock, November 18, 1943, replying to Stock’s letter congratulating him on election to the Arthur Balfour Professorship ( Bennett 1983 , p. 264)]. All things considered, Fisher did not have a high academic opinion of his predecessor. I give some of the reasons for this below. Punnett had gone to his Somerset retirement before Fisher returned to Caius, and although they overlapped as Fellows until Fisher died in 1962, Punnett did not return often and there is no corporate memory of their interaction when he did.

The story of Punnett’s friendship with the mathematician G. H. Hardy and how it led to Hardy’s 1908 discovery of “Hardy–Weinberg equilibrium” at the same time as W. Weinberg’s has often been told, not always correctly. In itself it reveals little of Punnett except that he was puzzled by something that really is extremely simple, and he had to get Hardy to set him straight. The fullest and, I hope, most accurate, account is to be found in a recent Perspectives ( Edwards 2008 ).

Later, when writing his book Mimicry in Butterflies , Punnett (1915) appealed to Hardy for some more mathematical help. He wanted to know the effects of selection at a single Mendelian diallelic locus under random mating, and Hardy, perhaps aware of the amount of computation involved, passed the problem on to his Trinity pupil H. T. J. Norton. The results were published in tabular form in Appendix I of Punnett’s (1915) book (and reprinted in Provine 1971 ). They were very influential, among other things inspiring J. B. S. Haldane to initiate his long series of articles on selection. Haldane was appointed Reader in Biochemistry at Cambridge in 1923, with a Fellowship of Trinity, and wrote that in 1922 Norton had shown him some calculations that were eventually published in 1928 (Haldane 1927; Norton 1928). Provine (1971) may be consulted for further details and Charlesworth (1980) for details of “Norton’s theorem.”

In 1917 Punnett again sought Hardy’s help over a similar problem, and this time Hardy himself calculated how slowly a recessive lethal is eliminated from a population, thus apparently discrediting the eugenicists’ claim that deleterious recessives could be eliminated in a few generations ( Punnett 1917b ). However, Fisher (1924) countered that these calculations “have led to a widespread misapprehension of the effectiveness of selection.”

Punnett (1930a) reviewed The Genetical Theory of Natural Selection (Fisher 1930a) for Nature . It was not friendly. Fisher (1930b) replied in a letter to Nature , to which the editor allowed Punnett (1930b) an immediate rejoinder. We now know, what Fisher could not have known at the time, exactly what Punnett reported to the Royal Society about Fisher’s “1918” article ( Norton and Pearson 1976 ): “I have had another go at this paper but frankly I do not follow it owing to my ignorance of mathematics.” He ended “I do not feel that this kind of work affects us biologists much at present. It is too much of the order of problem that deals with weightless elephants upon frictionless surfaces, where at the same time we are largely ignorant of the other properties of the said elephants and surfaces.” It was not to be expected that a man of such opinion would, only a dozen years later, be able to offer an informed assessment of The Genetical Theory , and Punnett seemed to admit as such: “Probably most geneticists to-day are somewhat skeptical as to the value of the mathematical treatment of their problems. With the deepest respect, and even awe, for that association of complex symbols and human genius that can bring a universe to heel, they are nevertheless content to let it stand at that, believing that in their own particular line it is, after all, plodding that does it.” Leonard Darwin wrote to Fisher “I am rather sorry they picked out an old discontinuous stick-in-the-mud like Punnett to review you in Nature . But to get 5 columns is an excellent advertisement. My father would have been much pleased with such a review of the Origin , and merely carefully noted the points to answer in his next edition. I think you may be well pleased. I never had so long a review” ( Bennett 1983 , p. 131).

In the review Punnett advanced his mutationist position: “Throughout the book one gets the impression that Dr. Fisher views the evolutionary process as a very gradual, almost impalpable one, in spite of the discontinuous basis upon which it works.” He touches on melanic moths, on poultry, and on mimicry, subjects on which he was well informed as a naturalist, and ends up by complaining about Fisher’s English. Bennett (1983 , p. 35) reports that the review “was a great disappointment to Fisher,” but one wonders whether the disappointment was more over the choice of reviewer than the content, because Fisher knew Punnett well enough not to have expected anything else from him. Fisher’s response listed six points (“misstatements or other slighter misrepresentations”), and Punnett attempted to answer them. The exchange served only to emphasize the magnitude of the scientific gulf that separated the first two holders of the Arthur Balfour Professorship of Genetics.

Reginald Crundall Punnett owed his academic career and reputation to the good fortune of being invited by William Bateson to join him as his partner in undertaking breeding experiments in both plants and animals in the heady days that followed the rediscovery and appreciation of Mendel’s article at the beginning of the 20th century. Having made a signal contribution to these studies his good fortune continued when he found himself the natural alternative to Bateson to occupy the Arthur Balfour Professorship of Genetics at Cambridge when Bateson declined it. Thereafter he lived the comfortable life of a Professor between the wars, provided with a house by the University, a Fellowship by his College, and the absence of pressing duties by either.

But one should not belittle the diagram that bears his name, any more than one should belittle Venn’s famous logic diagram, just because it is simple. It served a need so well that it is difficult to see how the complex pattern of inheritance of flower color in the sweet pea could have been unraveled without it. The discovery of partial linkage depended on the knowledge thus gained. Bateson (1909 , p. viii) wrote “In 1904 I had the good fortune to gain Mr. R. C. Punnett as a partner. Since that date we have worked in close collaboration, and the work that we have thus done has been in every sense a joint product, both as regards design, execution, and interpretation of results.” But he was careful to attribute the diagram to Punnett, as we have noted.

Genetics was taught twice a week, at five o’clock in the Michaelmas term, by R. C. Punnett … . He was a mild man with an overdominant wife who had been a major tennis player. Her opponents must have been terrified. Punnett had fine collections of Chinese porcelain and Japanese prints in a delightful house backed by an experimental garden, and he devoted himself largely to the genetics of sweet peas. The Punnetts gave Sunday lunches with superb wine to an incongruous set of students, half biological intellectuals, half athletes, all I think men. Only about half a dozen students took Punnett’s course. … The chromosome theory was still widely debated. Bateson was usually skeptical, though I know he accepted it for about a fortnight before his death. Punnett tended to be more receptive to the idea. One evening the high point of the course arrived unexpectedly; Punnett came in demurely and then announced that he had just finished all the calculations of linkage of the various characters he had studied in the sweet pea and that indeed there were as many linkage groups as chromosomes. The chromosome theory had worked for a plant as well as an animal and therefore might reasonably be expected to be of general validity (Hutchinson 1979, p. 99).

But I leave the last word to Joseph Needham ( Needham 1967 ), the Master of Caius: “Punnett also had a highly scholarly side, being greatly interested in the history of biology and possessing a notable library of its seventeenth and eighteenth-century literature. Unfailingly helpful and charming to younger colleagues, he would present them sometimes with rare books, and encourage them in their work in ways which they could never hope to repay. We greatly cherish his memory and record this for the information of later generations.”

I am grateful to Peter O’Donald for the reference to Hutchinson (1979) and to Axel Zeitler for help in understanding Correns (1900).

Balfour A J , 1930   Chapters of Autobiography , edited by   Dugdale E . Cassell , London .

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• Bateson-Punnett Notebooks

Poultry Notebooks

Rabbit notebooks, sweet pea notebooks.

Treasure your exceptions! When there are none, the work gets so dull that no one cares to carry it further" William Bateson, The Methods and Scope of Genetics, 1908, p.19

William Bateson (1861-1926) and Reginald Punnett (1875-1967) were the founders of experimental genetics in Britain and the main advocates of Gregor Mendel's models of inheritance. Through their collaborative experiments on poultry and sweet peas, Bateson and Punnett discovered some of the fundamental processes of Mendelian genetics, including complementation and the first example of autosomal (nonsexual chromosome) linkage. Their experiments are recorded in a series of laboratory notebooks acquired by Cambridge University Library from the Department of Genetics, a selection of which is now presented here.

The digitised notebooks span the period 1898-1910 and include two major sets containing records of poultry breeding and sweet pea crosses, along with notebooks recording their experiments on rabbits and on a range of plant species.

Entries show evidence of at least two different handwritings and it is likely that they were made by Bateson, Punnett, and various assistants, primarily women. Bateson is recorded as having had a series of assistants, many of whom were Newnham students reading the Natural Sciences Tripos. One of his main collaborators was Edith Rebecca Saunders, a lecturer in Biology in Newnham, who was also interested in the genetics of plants. Bateson, Saunders and Punnett published a series of important papers between 1902 and 1910 which confirmed the general applicability of Mendel’s work, but extended it by the discovery of linkage and complementation. Bateson’s association with Newnham may have come about because his mother, an advocate for female emancipation, was an early member of the Newnham college council. Female students were allowed to take courses in Cambridge at that time, but were not allowed to graduate, being given a certificate instead of a degree.

In the years 1890-1900 there was considerable debate over the cause of discontinuous variation (fur or feather colour, for example) versus continuous variation (characters such as size or weight), and this had become an active argument following on from Darwin’s observations on the role of natural variation in the origins of speciation. Bateson disagreed with the Darwinists, and his interests lay in studying discontinuous variation. At that period, Mendel’s work had not yet been rediscovered, and Bateson and others were still trying to work out how variations in visible characteristics were specified and inherited.

Bateson’s views were not in accord with the scientific establishment of Cambridge, who were largely Darwinists. Perhaps because of this, Bateson found it difficult to get a permanent position in the University, and also to find facilities to carry out his research. He kept many of the chickens which he used for his poultry breeding experiments in his own garden in Merton House, Grantchester, and he grew sweet peas both in the Botanic Garden and at a farm, the location of which remains obscure.

Bateson’s joint experimental work with Punnett ran from 1903 until 1910 when Bateson became director of the John Innes Horticultural Institute. They continued to collaborate by founding the Journal of Genetics together, which they edited jointly until Bateson’s death in 1926.

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Concept 5 Genetic inheritance follows rules.

• Reginald Crundall Punnett (1875-1967)

William Bateson (1861-1926)

William Bateson was born in Whitby , England. As a young boy, Bateson was asked what he wanted to be. He replied that he wanted to be a naturalist, but if he wasn't good enough then he would have to be a doctor. Bateson was not a star student - he didn't see the value of learning the "classics," and favored the natural sciences. In 1878, Bateson entered St. John's College at Cambridge University . His father was the master of the college at the time. As a student and later a researcher in Cambridge, Bateson was interested in species variation and heredity. He traveled to the Central Asian steppe and collected data on how environmental conditions relate to variation. In 1894, he published a book Materials for the Study of Variation based on his observations. In this book, he outlined the experimental approach that should be used to study inheritance. He was designing Mendelian experiments.

Around 1897, Bateson began doing some of these hybrid experiments with poultry and butterflies. When he read De Vries' and Mendel's papers, Bateson recognized the importance of "Mendelian Law," especially given his own experiments. By 1902, Bateson had translated Mendel's works into English and was a strong supporter of the Mendelian laws of inheritance. Bateson is credited with coining the terms "genetics," "allelomorphs" (later shortened to allele), "zygote," "heterozygote" and "homozygote." In 1908, as a Professor of Biology at Cambridge, Bateson helped establish the Cambridge School of Genetics .

Bateson left Cambridge in 1910 to accept the Directorship of the John Innes Horticultural Institute at Merton. He continued to have ties to Cambridge, collaborating with R. C. Punnett on genetic experiments and publications. Bateson and Punnett co-founded the Journal of Genetics in 1910.

Bateson's work and Bateson himself influenced other biologists and scientists such as Archibald Garrod , Thomas Hunt Morgan , and Charles Davenport . Bateson had a combative, forceful personality, well suited to his self-appointed role of Mendel advocate. However, Bateson was reluctant to believe in the chromosomal theory of inheritance. He was vocally antagonistic to the idea and it wasn't until 1922 after a visit to Thomas Hunt Morgan's fly lab that he publicly accepted chromosomes and their role in heredity.

Bateson's family life was quite tragic. One of his sons died just before the end of WWI, another committed suicide in 1922.

How important is it for scientists to work together and be aware of each other's results?

Funded by --> The Josiah Macy, Jr. Foundation © 2002 - 2011, DNA Learning Center , Cold Spring Harbor Laboratory . All rights reserved.

• MOLECULES OF GENETICS
• GENETIC ORGANIZATION AND CONTROL

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Weldon, Bateson, and the origins of genetics: Reflections on the unraveling and rebuilding of a scientific community

* E-mail: [email protected]

Affiliations Division of Genetic Medicine, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America, Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America, Department of Psychiatry and Behavioral Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America, Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America, Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America

• Lea K. Davis

Published: October 27, 2022

• https://doi.org/10.1371/journal.pgen.1010379
• Reader Comments

Citation: Davis LK (2022) Weldon, Bateson, and the origins of genetics: Reflections on the unraveling and rebuilding of a scientific community. PLoS Genet 18(10): e1010379. https://doi.org/10.1371/journal.pgen.1010379

Editor: Jonathan Flint, University of California Los Angeles, UNITED STATES

Copyright: © 2022 Lea K. Davis. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The authors received no specific funding for this work.

Competing interests: The authors have declared that no competing interests exist.

“ Science , like most forms of human activity , is occasionally liable to lose sight of its ultimate ends under a flood of controversy , the strugglings of personal ambition , or the fight for pecuniary rewards or less physical honors … But science, no less than theology or philosophy , is the field for personal influence, for the creation of enthusiasm , and, for the establishment of ideals of self-discipline and self-development.”—Karl Pearson [ 1 ]

More than a century has passed since the publication of R.A. Fisher’s 1918 paper “The correlation between relatives on the supposition of mendelian inheritance”. Celebrated across the world as a major turning point in the young science of genetics, the paper formally reconciled mendelian and biometric approaches to inheritance by introducing the concepts of variance and polygenicity and laying the groundwork for the complex trait liability threshold model, which remains highly relevant to modern human genetics [ 2 ]. While many in the field of human genetics are aware of this work, few are aware of the controversy that preceded it. It is an origin story for the field of human genetics, filled with both drama and discovery. The lessons herein resonate today as we continue to contend with the trials of hyper-competitive incentive structures, a workaholic academic culture, and larger-than-life egos that often hide the vulnerability we feel as mere mortals tasked with tremendous feats.

Now is an opportune time to revisit these origin stories of our field. Given the magnitude of the problems facing us today, there is an urgent need for larger and larger scientific communities to function healthfully. Anyone who has felt in their gut the awe and humility of discovery understands that we are not entitled to learn the secrets of the Universe, we labor to gain even the smallest insight. Individually, we will be wrong far more often than we will be right. In this tale, what began as a scientific debate between friends devolved into a bitter argument, creating a chasm in the scientific community that persisted for decades and arguably stalled the progress that Fisher’s paper later spurred. In a sense, this story can be viewed as a “morality tale” about the dangers of competitiveness, the responsibility of influential voices, and the importance of maintaining a profound sense of humility as a scientist. The following centers the very elements that complicate healthy team science—friendship, ego, and ambition, and illustrates how they were weaponized in a war between scientists that was said to have resulted in at least 1 casualty [ 3 – 6 ]. It is my hope that by shining a spotlight on the interpersonal aspects of doing science, we may deepen our appreciation for the profound and enduring impact that our interactions can have on the scientific questions we choose to answer, the methods we adopt, and how we conceive of “ground truth.”

The story began long before Fisher was born, in 1859, with the publication of Charles Darwin’s book On the Origin of Species [ 7 ]. Darwin, privileged by wealth and education, traveled widely at an early age and compiled detailed notes on flora and fauna across the world. He gained an international reputation when he introduced the scientific world and the lay public to his theories of evolution and natural selection. Darwin’s half-cousin, Francis Galton, who was interested in similar ideas, had also recently published a book on his travels titled “Narrative of an explorer in tropical South Africa.” Despite a Royal Geographic Society review claiming the book was written with much “manly humor and style” [ 8 ], it was no comparison to Darwin’s thesis. After the publication of his cousin’s book, Galton (who later became known as the “father of eugenics”), focused his attention on questions pertaining to human variation, heredity, and selection provoked by Darwin’s theories of evolution. During his career, he formalized the statistical concepts of correlation and regression and his influence loomed large on all the personalities involved in the conflict to come.

Twenty years after the publication of Darwin’s book (1879), the 2 most important players in this drama, William Bateson (1861 to 1926) and Walter Frank Raphael Weldon (1860 to 1906), met as undergraduates at the University of Cambridge. Despite their different backgrounds, the two shared a common interest in zoology and both made his home in academia. Bateson, whose father was Master of St. John’s College (a constituent college of the University of Cambridge), was on track to attend Cambridge since childhood. In contrast, Weldon was the first in his family to attend a University, though his father Walter Weldon was a celebrated chemist and innovator [ 9 ]. Weldon quickly developed a reputation in the zoology department for being a clear and insightful teacher. During their years at Cambridge, a friendship grew, and though he was only 1 year older, Weldon became a peer mentor to Bateson.

By this time, the theory of evolution was widely accepted within scientific circles; however, the mechanisms through which new species arose remained a great mystery and was one of the most compelling scientific questions of the day. Bateson and Weldon were captivated and each set out to understand the process of speciation. Both men were also highly influenced by Galton’s work which, by then, had provided much of the foundation for modern statistics. Further, they were both personally acquainted with Galton and the three corresponded regularly. During the next decade, Bateson, Weldon, and Galton theorized widely on whether speciation was due to a slow and continuous process of selective breeding or could occur due to a major and rapid biological change (i.e., saltation).

Weldon and his wife Florence (nee Tebb) began collecting and studying wild populations of shrimps and crabs hoping to understand the relationship between continually varying morphological features within and between species. Weldon was quantitatively minded but lacked in computational skill [ 10 ]. Florence, who graduated from Girton College, Cambridge, was schooled in computation and a rigorous analyst. Together they collected, measured, and recorded dozens of anthropometric features on hundreds of samples, and Florence computed hundreds of descriptive statistics. Eventually, they sought a collaboration with Karl Pearson upon his joining the faculty of the University College London in 1892. It was their data on wild crab populations and questions about the continuous characteristics of these populations that provided Pearson both the means and motivation to develop the statistical methods for which he eventually became famous. Pearson once said, “Any mathematician could have done what I have done, a dozen or so better, especially if they had suggestions from Weldon almost daily at lunch for 4 or 5 years” [ 11 – 13 ]. Through years of painstaking data collection and analysis, the team eventually began to realize that anthropometric traits that distinguished different crab species also varied greatly within species. Indeed, upon the collection of enough data, even “dimorphic” traits appeared continuous. Thus, they came to believe that the most likely mechanism to explain evolution was slow and gradual natural selection.

Furthermore, Weldon believed the theoretical proof of this biological process could only be achieved through mathematics claiming that “The questions raised by the Darwinian hypothesis are purely statistical, and the statistical method is the only one at present obvious by which that hypothesis can be experimentally checked” [ 14 ]. This was not to say that he found no use for experimental data in uncovering potential mechanisms, only that he firmly believed in the necessity of statistical approaches to populations [ 15 ]. Nevertheless, this was not a popular opinion. As Pearson later remembered, “The very notion that the Darwinian theory might after all be capable of statistical demonstration seemed to excite all sorts and conditions of men to hostility. Weldon, instead of being allowed to do his own work in his own way, had to be constantly replying to letters, some even 18 sheets long … These letters were not sympathetic and suggestive, but mostly purely controversial,” [ 1 ]. Nevertheless, Pearson continued to work with Raphael and Florence Weldon and presented ideas that emerged from the crab populations including the concepts of standard deviation, covariance, and coefficient of variation [ 16 – 19 ]. It was also through Weldon that Pearson eventually met Galton. Galton became a life-long mentor and friend to Pearson and the two became so close that after Galton died, Pearson spent 20 years writing his definitive biography [ 20 ].

It should be noted that while Weldon believed in the necessity of statistical evidence to confirm observations, particularly in wild populations, he also valued laboratory experimentation and mechanistic understanding. In addition to his work on wild populations, he collaborated on breeding experiments using Japanese waltzing mice to evaluate segregation patterns in coat color, among other traits. Indeed, unpublished manuscripts (“ The Theory of Inheritance ”) written by Weldon in his later life [ 21 ] attempted to bring statistical and mechanistic insights gained through analysis of both wild populations and experimental studies together into a unified theory [ 15 , 21 ].

Meanwhile, Bateson worked diligently to perform carefully controlled experimental crosses of plant species in the Cambridge botanical gardens and frequently observed segregation of traits that clearly behaved as dimorphic (e.g., petal color). Based on these observations, he became convinced of the potential for “sporting mutations” (i.e., rare alleles with large phenotypic impacts) to drive evolutionary leaps. Bateson faced his own share of political pressure aimed at his theories and methods. The Director of the Morphological Laboratory at Cambridge, Adam Sedgwick, did not think highly of Bateson’s work. In a letter to his sister, Bateson confessed that “Sedgwick tells me he would not wish me to have Weldon’s lectureship if W. goes to University College. He says, as I expected, that I have gone too far afield and that my things are ‘a fancy subject’” [ 22 ].

The situation at Cambridge worsened for Bateson as he began expanding his research group. Bateson was sympathetic to the women’s suffrage movement in which his mother Anna Aitkin and sisters Margaret, Anna, and Mary Bateson were prominently involved ( Box 1 ). He welcomed women into his laboratory group. Some of the first papers from his group were coauthored by his sister Anna who also worked with Francis Darwin (botanist and son of Charles Darwin) during her studies at Cambridge. However, Sedgwick strongly disapproved of women in the academy, and this principled position cost Bateson throughout his career. Though he was employed at Cambridge for the entirety of his career, his promotion was overlooked for more than a decade. Nevertheless, his integrity remained intact and his collaborations with many female scientists including Edith Saunders, later referred to as the “mother of British plant genetics” [ 23 ], were incredibly productive ( Box 2 ).

Box 1. The price of feminism

We would be amiss to neglect the larger social context in which Weldon, Bateson, and their female colleagues were working. Women’s suffrage was a major political debate that impacted the career trajectory of men and women who supported women’s right to vote. In 1906, Mary Bateson was one of nearly a dozen women and men comprising a Women’s Suffrage Deputation who petitioned the Prime Minister from the floor of the House of Commons. Mary spoke on behalf of “women who are Doctors of letters, science, and law in the Universities of the United Kingdom and of the British Colonies ….who believe the disenfranchisement of one sex to be injurious to both and a national wrong in a country which pretends to be governed on a representative system”. (Women’s Suffrage Deputation, May 19, 1906; Received by the Prime Minister, Sir Henry Campbell-Bannerman, published by the National Union of Women’s Suffrage Societies, 25 Victoria Street, Westminster London, S.W.)

Box 2. Note on the important contribution of Edith Rebecca Saunders to the early discipline of genetics

Edith Rebecca Saunders was an influential early geneticist. Her experiments led to the characterization of the “allelomorph” (i.e., heterozygote and homozygote), many decades before Rosalind Franklin’s groundbreaking work characterizing the structure of DNA. She served as the Vice President of the Linnean Society, the 1920 President of the Botanical Section of the British Association for the Advancement of Science, and the 1938 President of the Genetical Society.

During these years, Weldon and Bateson corresponded often to debate the merits of gradual selection versus sporting mutation as well as the best methods of evaluation. In an 1888 letter, Weldon wrote to Bateson, “I have not written to you for a long time because I have the spirit of polemic upon me: and I have wished to consider carefully the words I should say to you. In the first place, I will tell you 3 sets of things which ought as it seems to me to annoy you …” He ended the letter lightheartedly by saying, “And when are you coming to crush me???” [ 6 ]. The friendly teasing in these correspondences foreshadowed the break that was to come.

In 1894, Bateson published the book “Materials for the study of variation treated with especial regard to discontinuity in the origin of species”. He presented the experimental crossing methodology that his team employed and used it to argue the case for the importance of saltation. Weldon was asked to write a critique of the book for Nature , and this seemed to mark the beginning of the public end to their friendship. While it was considered an overall positive review, he criticized Bateson’s thesis of evolution by saltation. Weldon was unimpressed by Bateson’s arguments stating “If the criticism and enunciation of opinions had been performed with the same care as the collection of facts, the commentary which runs through the book would have gained in value, and several inaccuracies, partly due to want of acquaintance with the history of the subject, would have been avoided” [ 24 ]. Bateson’s next move signaled that he was both hurt and angry. He turned to Galton to vent his frustration in a series of letters that heavily criticized Weldon’s analysis of wild crab populations [ 25 ].

A year later, the situation intensified when William Turner Thiselton-Dyer, Director of the Royal Botanic Gardens in Kew, wrote a letter to the editor of Nature in which he praised work recently presented by Weldon and Pearson stating, “I entirely agree with him in minimizing the value of ‘sports’ in evolution” [ 26 ]. This drew severe criticism from Bateson who responded the next month with his own letter to Nature announcing that he “…ventured to deal with this case because it seems to be generally supposed by those not acquainted with the facts, that the origin of the modern florists’ flowers has in general been very gradual”. Eventually, Weldon also weighed in, arguing that Bateson omitted pertinent information in his letter and that his “emphatic statements are simply evidence of want of care in consulting and quoting authorities referred to.” Bateson furiously replied, “Upon what grounds [Weldon’s] statement has been made the reader shall now learn, not perhaps without astonishment”. Weldon finally ended the quarrel saying, “Enough has been said to show that Mr. Bateson’s original evidence does in fact bear the interpretation I put upon it…Having done this, my interest in the matter ends, and I do not propose to speak further upon it” [ 27 ]. The playful argumentativeness that characterized their earlier written exchanges transformed into bitter antagonism as each became more entrenched in his own methodology and results and suspicious of the other. Eventually, Weldon wrote privately to Bateson saying, “Dear Bateson, I can do no more. First, you accuse me of attacking your personal character, and when I disclaim this, you charge me with a dishonest defense of someone else…If you insist upon regarding any opposition to your opinions concerning such matters as a personal attack upon yourself, I may regret your attitude but I can do nothing to change it” [ 28 ].

For the next few years, Bateson, Saunders, and Punnett continued to selectively breed plants and publish observations of discontinuous traits while the Weldons’ continued to gather large amounts of data from wild populations of crabs and collaborate with Pearson in London to develop statistical methods of analysis. The next plot point in the story occurred at the turn of the century when Mendel’s work was “rediscovered.” Hugo de Vries, a botanist from Austria, who was aware of Mendel’s work, attended the 1899 conference of the Royal Horticultural Society where he heard a lecture by Bateson describing the breeding experiments that he and Saunders were performing on flowering plants in Cambridge. Realizing the similarity to Mendel’s earlier pea plant experiments, De Vries published a paper in 1900 referring to the original work of Mendel in a footnote. The year 1900 marked the “rediscovery” of Mendel’s laws by De Vries, Correns, and Tschemark, and gave Bateson the independent evidence that he was seeking ( Box 3 ). He became a huge supporter of the “mendelian” theory and again, wrote to Galton, saying “In case you may miss it… Mendel’s work seems to me one of the most remarkable investigations yet made on heredity, and it is extraordinary that it should have got forgotten.” [ 29 ]. Bateson became an ardent supporter of the mendelian model of inheritance, and in 1909, Bateson translated Mendel’s work from the original German into English. Incidentally, he also named his youngest son Gregory after Gregor Mendel.

Box 3. Recent interpretations challenge the traditional account of the rediscovery of Mendel’s work

Shan argues that rediscovery is the wrong term to describe the use of Mendel’s work in the subsequent efforts of de Vries, Correns, and Tschemark. All 3 reported Mendel’s observations, but then went on to extrapolate from his work ideas that supported their own discoveries. For example, Shen argues that De Vries, not Mendel, proposed the ideas of dominance and segregation of alleles that he supported with the ratios reported by Mendel [ 15 ].

But Pearson and Weldon were skeptical of mendelian ratios believing the results were “too good to be true.” Weldon noted that in the wild, peas often varied more continuously from yellow to green. He argued that Mendel’s results may have been an artifact of the extensive inbreeding required to obtain the pure green and yellow lines prior to the hybridization experiments. His skepticism of mendelian ratios was fed by a larger concern over what he perceived as a lack of quantitative rigor in the field. In the year before Mendel’s work was rediscovered, he wrote to Pearson saying, “The contention ‘that numbers mean nothing and do not exist in Nature’ is a very serious thing, which will have to be fought. Most other people have got beyond it, but most biologists have not. Do you think it would be too hopelessly expensive to start a journal of some kind?” Weldon and Pearson (in consultation with Galton) subsequently established the journal Biometrika that produced its first issue in 1901. By 1902, the two schools of thought were cemented and colloquially named, the Mendelians (Bateson, Saunders, and Punnett) in Cambridge, and the Biometricians (Weldon and Pearson) in London. By 1904, about 15 years after the argument first began, civility was so eroded that the editor of Nature refused to publish any more letters between Weldon and Bateson on the issue of saltation versus continuous selection.

Eventually, the tension erupted in person at the 1904 meeting of the zoological section for the British Association for the Advancement of Science. The meeting was held at Cambridge, the Mendelians’ turf, and Bateson was the president of the zoological section of the society. It was no surprise that he used his presidential address to lecture on the controversy saying, “For if any one will stoop to examine Nature in those humble places… he will not wait long before he learns the truth about variation… Again and again the circumstances of their occurrence render it impossible to suppose that these striking differences are the product of continued selection, or, indeed, that they represent the results of a gradual transformation of any kind” [ 30 ]. Bateson’s words provoked an argument with Weldon on the spot. The argument grew heated and according to reports of the session, conference goers who at first were shifting uncomfortably in their seats eventually began to congregate around the embattled leaders of each side. Finally, the chair of the session, who could not subdue the animated crowd announced in exasperation “Let them fight it out!” [ 31 ]. The event was so explosive that 2 years later, when Weldon died suddenly of pneumonia, the New York Times described the scene in his obituary saying that “The debate, which was conducted before a large and somewhat agitated audience, resolved itself into a dialectical dual between the president of the section [Bateson] and Professor Weldon, and developed quite a considerable amount of heat” [ 32 ].

Over the next 2 years, the argument overtook both men. Weldon was seemingly obsessed with disproving what he perceived as a narrow interpretation of the mendelian hypothesis of inheritance (particularly dominance) in each subsequent paper in which it was proposed. His last work, “ Theory of Inheritance ,” an unpublished book with 6 manuscript chapters (historical documents held at University College London), incorporated experimental data testing mechanistic hypotheses underlying his statistical observations [ 21 ]. Shan [ 15 ] and others [ 33 ] argue that this manuscript presents a unified theory which may indeed have been the first attempt to reconcile Biometry and Mendelianism. He worked excessively long hours day after day and for many months refused a break, saying “I really want a holiday, but I cannot leave this thing unsettled” [ 4 ]. Pearson was concerned and eventually persuaded Weldon to take a vacation. The families adjourned to the English seaside for the Easter break, and it was there that Weldon caught a chest infection that developed into pneumonia. He died a few weeks later at the young age of 46. Pearson, and many others who knew Weldon, believed his premature death was in part due to frenzied overwork and stress that left him physically weakened and unable to fend off the infection. Of his friend, Pearson said: “He was by nature a poet, and these give the best to science, for they give ideas” [ 1 ].

After Weldon’s death, the raw bitterness of the Mendelian–Biometrician debate gave way to a quieter resentment that seethed between Pearson and Bateson for another decade, and Weldon’s manuscript book remained in archives. Bateson found that his influence was profound in the United States where mendelian genetics took firm root while London remained the stronghold of the Biometricians. Mendelian genetics caught on early and spread rapidly in the US, in part due to promotion by eugenicists who used genetic determinism to mobilize a racist and classist agenda that permeated US genetics and governmental policy until well after World War II. Later, after distancing genetics from eugenics, theories of mendelian inheritance continued to be the primary model taught in the US. Indeed, the consequences of this community divide can still be seen today in a comparison between UK and US genetics school curriculum.

Twenty-six-year-old Ronald Aylmer Fisher entered the fractured field in 1916, a decade after Weldon’s passing. By this time, the division between the Biometricians and the Mendelians was older than Fisher himself and had profoundly shaped the new field of genetics and an entire generation of zoologists. Fisher was in an ideal position to bridge the divide. Trained as a mathematician but working at Cambridge, the home of the mendelian experimentalists, Fisher was open to the possibility of a simple third solution that unified the observations of both sides. His paper describing this solution was first communicated by Leonard Darwin (Charles’ nephew) to the Royal Society in 1916. The paper included extensive mathematical proofs supporting the central thesis that “In general, the hypothesis of cumulative mendelian factors seems to fit the facts very accurately.”

The paper represented the potential for a formal reconciliation between the positions of the Biometricians and the Mendelians. Reginald C. Punnett and Pearson, who had been so close to the heart of the conflict between Bateson and Weldon, were asked to review. The paper was heavily mathematical and from Punnett’s perspective, too theoretical. Of the thesis, Punnett stated “I do not feel that this kind of work affects us biologists much at present. It is too much of the order of problem that deals with weightless elephants upon frictionless surfaces, where at the same time we are largely ignorant of the other properties of the said elephants and surfaces” [ 34 ]. Pearson’s review, which he started by acknowledging he was “overfussed with other work,” was similarly dismissive and asserted that the paper was of little interest to the mathematically minded and unlikely to be persuasive to biologists. He closed by stating that “Whether the paper be published or not should depend on mendelian opinion as to the correspondence of the authors hypotheses with observation, and the probability that mendelians will accept in the near future a multiplicity of independent units not exhibiting dominance or coupling” [ 34 ]. Though it was not formally rejected, the paper was considered too low impact by the journal and was eventually withdrawn [ 34 ]. It was published 2 years later, in 1918, in the Transactions of the Royal Society of Edinburgh. Today, “The correlation between relatives on the supposition of mendelian inheritance” is considered one of the most influential papers in human genetics as it provided a foundation from which the polygenic model of disease and many sophisticated molecular and quantitative approaches subsequently emerged.

However, it would still take many years of healing before the human genetics community truly integrated these ideas into praxis. As the field of medical genetics emerged, work in the US was almost exclusively focused on single-gene disorders for decades. The biometrician view of polygenicity and continuous distributions of genetic liability, which became a staple of genetics curriculum in Europe, was less frequently taught in US classrooms. Even today, many genetics students reach graduate school in the US without ever having been exposed to Fisher, Weldon, or a polygenic model of disease. In contrast, even most US middle school students have heard of Mendel’s principals of inheritance. The comparative lack of quantitative genetics in the US can be directly traced back to these early days and reminds us that even our local science culture can be shaped by the personality and priorities of distant scientists with a bully pulpit.

Weldon and Bateson were, as most scientists are, fanatical truth-seekers who shared the radical belief that nature’s truths are discoverable. Their legacy demonstrates that despite the nobility and beauty of this shared journey, we move slowly, hampered by the ignoble baggage that complicates our relationships. The lesson from this story is simple, but not easy. Science without humility and community slows our collective understanding. The history of science in the Western academy is fraught with stories like this one. In Western cultures, we often attribute discovery to individuals instead of communities, effectively making scientific discovery appear highly personal and individualistic. Furthermore, our competitive instincts to win arguments are seeded and nurtured by academic institutions that reward “being right” and punish mistakes without acknowledging that we can rarely have the former without the latter. Further, in today’s climate of rapid-fire response on social media, the community norms for engaging in scientific debate can easily erode even further. None of us is immune to the deafening arrogance of competition or the blinding lure of peer admiration, and this individualistic culture leaves science itself vulnerable as fractures develop in the community. These fractures then slow collaboration and provide a breeding ground for disinformation campaigns, the scale of which continues to grow.

My own experience is obviously limited, and yet, there may be value in sharing that experience. After 20 years in academic science, and a range of team–science interactions, it is my observation that when a scientific community is guided by a philosophy of “open-hearted curiosity,” healthy collaborations are born and important discoveries follow. What does this mean? Unfortunately, open-heartedness (and even open-mindedness) can sometimes be perceived as a weakness, somehow lacking in scientific rigor. But rigor should not be confused for ruthlessness, and open-hearted curiosity does not imply a lack of skepticism. In fact, skepticism is inherent to curiosity. Richard Feynman once said, “Science is the belief in the ignorance of experts,” and went on to explain that scientists must be trained to “both to accept and to reject the past with a kind of balance that takes considerable skill.” I argue that curiosity is the fundamental driver of this balance. The curious person does not accept assertions without evidence, they need to see, poke, and prod the data for themselves.

Curiosity alone cannot sustain healthy collaboration, but open-heartedness can protect it from toxicity. The open-hearted scientist is willing to share what they know and willing to be open and honest about what they do not know or do not yet understand. For academicians, this strikes at the heart of a vulnerability that most achievement-oriented education systems have implicitly encouraged us to hide. How can we be “experts” in our field and admit that we are ignorant? And yet, if we agree with Feynman’s astute observation of science, we are compelled to so. From an open-hearted perspective, we can shed the judgement of our ignorance, and instead appreciate that it is the raw material of future discovery. The wonderful thing about this approach is that it further compels us to question everything from our own motivations to our understanding of the data in front of us. Open-hearted curiosity provides a safe space for us to deepen our questioning. The open-hearted person further recognizes that good ideas can come from anywhere, listens without prejudice, and values the humanity of those around them. Indeed, approaching scientific problems with open-hearted curiosity is a rigorous practice that requires a great dose of humility and relentless perseverance.

Could Bateson and Weldon have benefited from open-hearted curiosity? Theirs was an era of robust debate and independent science. Their debates took on a sporting quality, as exemplified during the 1904 conference. But this model of scientific discourse may have been doomed from the beginning. After all, in the end, debate for sport is unambiguously about winning. Each side digs their heels in and aims to persuade as many people as possible. There is very little room for ambiguity and admitting any vulnerability or questioning one’s own view is a game-ending move in a sporting debate. But in a culture that explicitly values the search for truth, and not the ego of the scientist, scientific debate has an entirely different quality and outcome. It is no longer a sport with a single dominating champion. It becomes a scaffolded work of art, an improvisational jazz piece composed through individual creativity and communal effort. In this style of debate, parties lock intellects and together come to a deeper understanding of the world around them. In retrospect, I wonder how far Weldon and Bateson, together, could have pushed the field if they had matured in a climate of open-hearted curiosity.

When we engage each other with ego, we risk contaminating the worthiness of our shared pursuit with our own self-interests. On the other hand, if we can adopt a cultural expectation of open-hearted curiosity and learn to recognize and soothe our own insecurities, if we can allow ourselves to be vulnerable about what we do not know, if we can trust each other to share honestly and without judgement or pretense, we can create a principled scientific community deserving of discovery. We have the awesome responsibility of understanding and communicating the stuff that makes us human. These are bigger questions than we can fathom alone, and we are never so worthy to learn the secrets of the universe as when we humble ourselves to their complexity.

Acknowledgments

I wish to thank Tad Davis, Nancy Cox, Naomi Wray, Peter Visscher, Sara Van Driest, Anthony (Tony) Capra, and Laurel Waycott for their encouragement and feedback on early drafts of this work.

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Agreeing and disagreeing, calculating and correcting, drawing lines and diagrams, conclusions, punnett squares and hybrid crosses: how mendelians learned their trade by the book.

Published online by Cambridge University Press:  09 December 2020

• Supplementary materials

The rapid reception of Gregor Mendel's paper ‘Experiments on plant hybrids’ (1866) in the early decades of the twentieth century remains poorly understood. We will suggest that this reception should not exclusively be investigated as the spread of a theory, but also as the spread of an experimental and computational protocol. Early geneticists used Mendel's paper, as well as reviews of Mendelian experiments in a variety of other publications, to acquire a unique combination of experimental and mathematical skills. We will analyse annotations in copies of Mendel's paper itself, in early editions and translations of this paper, and in early textbooks, such as Reginald Punnett's Mendelism (1905) or Wilhelm Johannsen's Elemente der exakten Erblichkeitslehre (1909). We will examine how readers used copies of such works to reproduce the logic behind Mendelian experiments, either by recalculating results, or by retracing the underlying combinatorial reasoning. We will place particular emphasis on the emergent role of diagrams in teaching and learning the practice of Mendelian genetics.

In 1901, the Austrian agronomist Erich von Tschermak (1871–1962) produced a critical edition of Gregor Mendel's (1822–84) paper ‘Versuche über Pflanzenhybriden’, and in the same year the Cambridge biologist William Bateson (1861–1926) published an English translation entitled ‘Experiments in plant hybridization’ in the Journal of the Royal Horticultural Society . Footnote 1 Tschermak's edition appeared as Volume 121 of the series Ostwalds Klassiker der exakten Wissenschaften (Ostwald's Classic Texts in the Exact Sciences). Though indicative of its astonishing reception history, historians have rarely noted the paradox that lies in the fact that a journal article, which a few botanists had lifted from obscurity only a year earlier, was almost instantaneously proclaimed to belong to the canon of the ‘exact’ sciences, aptly inserted between Marcello Malpighi's seventeenth-century treatise on plant anatomy and an important contribution to higher arithmetic by Carl Friedrich Gauss. Footnote 2 The discipline that Mendel supposedly founded, namely genetics, did not yet exist in 1901, and his alleged ‘discovery’ of laws of inheritance would remain contested for at least another decade, including accusations that Mendel had manipulated his data to fit his expectations. Footnote 3

In trying to explain the rapid reception of Mendel's paper, historians usually focus on its theoretical content. According to this account, most influentially promoted by Garland E. Allen, Mendel's model of particulate inheritance spoke to a new generation of biologists who turned against the phylogenetic and morphological research traditions of the nineteenth century. They endorsed a reductionist view of life, and an understanding of science that placed experimental and quantitative over comparative and qualitative methods. Footnote 4 Consolidation of Mendelian genetics was accordingly brought about by paradigm articulation and strategies of theory adjustment to experimentally produced anomalies. Footnote 5 This interpretation is complemented by another tradition that proposes that Mendel's theory and method became popular due to their potential applications in agriculture and medicine, especially eugenics. Footnote 6 Despite their differences, both interpretations fundamentally agree that Mendel's paper was read for its theoretical and practical content, which was epitomized in what most early geneticists agreed to be Mendel's most fundamental theoretical discovery, namely the ‘purity of the gametes’, or that gametes of hybrids are not themselves hybrid but remain ‘pure’, and hence recombine in sexual reproduction without interacting with each other. Footnote 7

In this paper, we want to follow up a complementary interpretation that has occasionally been proposed, namely that Mendel's lasting legacy consisted in the creation of a particular experimental system that combined advanced breeding methods – in essence, pure breeding and artificial cross-fertilization – with a mathematical notation to record, analyse and visualize experimental results on paper. Footnote 8 This interpretation, to be sure, insists not on a dichotomy between experimental practice and theoretical understanding, but rather on a difference in scope. Instead of concentrating on paradigms, or sets of theoretical and methodological commitments delineating broad scientific programmes, it focuses on particular tools or methods that are flexibly employed in different research contexts. Such tools or methods often prove to be ‘remarkably tolerant and adaptable to theoretical change’, as Bill Wimsatt puts it in an article dealing with the history of the Punnett square, a diagram which was crucial to the early history of genetics, as we will show as well. Footnote 9 Examining such tools in detail can help to explain why Mendelism rapidly spread in the early twentieth century although biologists continued to disagree about the theoretical interpretation of empirical results gained from Mendelian experiments and about the extent to which these results could be generalized. This perspective also draws attention away from the acrimonious debates that accompanied the rise of Mendelism and brings into focus the many researchers and practitioners who were solely interested in learning how to carry out and analyse the results of Mendelian experiments. In other words, this perspective invites us to read Mendel's paper, as well as the many articles and books that adopted his reasoning, as texts ‘to learn by’, or as texts that were supposed to communicate specific know-how rather than wide-ranging theoretical or methodological principles.

Our aim in the following is to provide evidence for this understanding of the rise of Mendelism. In addition, we also want to suggest a fruitful method of investigating how twentieth-century readers used print publications to re-enact and rehearse experimental and mathematical methods. In order to understand how readers used texts, we simply suggest looking for readers’ annotations. For this article, we have checked early editions and translations of Mendel's paper, as well as some important early Mendelian textbooks such as Reginald C. Punnett's Mendelism or Wilhelm Johannsen's Elemente der exakten Erblichkeitslehre . The book copies we consulted are part of library and archival collections or available online through the Internet Archive and other online repositories such as the Biodiversity Heritage Library and the Digital Collections of the Wellcome Trust. Footnote 10 Many of these publications did actually turn out to be annotated, often by notable (and lesser-known) scientists of the time.

We are far from being able to present results from a systematic study of readers’ annotations in Mendelian publications. Our sample of sources is biased by our specific interest in annotated book copies and by the limited number of libraries and archives we could visit in person. Footnote 11 Yet we are convinced that our sources at least indicate that early Mendelian texts were often read as treatises in applied mathematics and experimental design, and that the rapid reception of Mendelism can therefore partly be explained as the spread of a computational and experimental protocol. In addition, we believe that our findings have some intrinsic interest for more general and systematic questions regarding how readers in the early twentieth century interacted with scientific texts in order to internalize and visualize experimental and computational procedures, and how such interactions in turn were suggestive of new diagrammatic representations.

It is tempting to compare our results with the body of scholarship on early modern reading and note-taking practices. Footnote 12 Yet Mendel's position in the history of the life sciences is too idiosyncratic to consider his readers as representative. Footnote 13 When we occasionally comment on how the practices we observed in our twentieth-century material differ from what we know about corresponding practices in the early modern period, one should also keep in mind that we know hardly anything yet about reading and note taking in twentieth-century science. Footnote 14 What follows is therefore a first exploration of potential themes that should invite further empirical research and analysis on twentieth-century annotation practices.

We will approach the material we collected in three steps. In the first section of this paper, we will focus on reading marks and annotations that refer to the discursive content of the texts we have investigated. These annotations indicate that many readers focused on ‘how-to’ aspects of Mendelian experimentation, and were less interested in theoretical conclusions. The second section then turns to a peculiar behaviour we detected among many of our readers, namely the urge to repeat calculations, as is particularly evident from readers detecting and correcting errors. We interpret this as resulting from the need to practise computing procedures in order to understand and master them. The final section turns to visual representations in early Mendelian texts, and argues that there is a link between the visual expedients early readers used – mainly lines drawn to connect different elements of the text – and later diagrammatic representations of the combinatorial logic of Mendelism. The conclusion will then argue that this combinatorial logic, which seems trivial from today's perspective, was counterintuitive back then and needed to be internalized through an active engagement with texts, tables and diagrams.

When Ostwald founded the Ostwalds Klassiker der exakten Wissenschaften series in 1889, it was mainly for educational purposes; his hope was that new generations of scientists could learn ‘what contributions to science, which have stood the test of time, look like and how they came about’. Footnote 15 Tschermak published a revised, second edition of Mendel's paper in 1909, and the volume would undergo four more print runs until 1940. The English translation of 1901 likewise went on being published, first as the second chapter of Bateson's Mendel's Principles of Heredity: A Defence (1902), then appended as ‘Part II’ to the third edition of the same book (1913). Bateson's translation was furthermore included as an appendix in William E. Castle's Genetics and Eugenics (1916). The publisher of this volume, Harvard University Press, decided to issue Mendel's paper separately in the form of an inconspicuous brochure, which also underwent several print runs. There was thus a constant demand for accessible editions and translations of Mendel's paper among students and researchers in the biological sciences. In addition, the period saw the production of many introductory texts on Mendelism, which in turn were often translated into several languages. Footnote 16

What is striking about the annotated copies of Mendel's paper that we inspected is that annotations are not uniformly distributed in the text. Especially the sections at the end of Mendel's paper, which proposed and discussed a theoretical explanation for the empirical results presented in the preceding sections, usually lack annotations. Footnote 17 Moreover, none of the copies we inspected showed signs of conceptual disagreement between Mendel and his readers. The most frequent annotations consist in marginal lines and underlinings that drew attention to parts of the text the reader deemed important. A typical example is provided by a copy of Tschermak's edition of Mendel's text, which is conserved in Berlin. In this book, a reader underlined a few words from the passage describing what is sometimes referred to as the ‘first law’ of Mendel, or the ‘law of uniformity’. Almost identical reading marks can be found in the same copy against Mendel's definition of recessive and dominant traits and his first statement of the 3:1 ratio according to which traits segregate. Footnote 18 We found similar reading marks against what are conventionally considered Mendel's most important contributions in a number of other editions. Footnote 19

The lack of exegetical or critical comments stands in striking contrast to what scholars have revealed about early modern reading practices. As Ann Blair has long argued, early modern readers of natural philosophy placed what they read within a web of existing knowledge through methods of marginal annotation and commonplacing. Footnote 20 More recently, Renée Raphael has shown that this also applies to works of the Scientific Revolution, such as Galileo Galilei's Discorsi , that are deemed to have radically dissociated themselves from the ‘bookish’ methods of traditional learning. Footnote 21 We did not find any evidence of this kind of topical engagement with Mendel's paper, nor did readers use his text to correct or complement existing knowledge, as eighteenth-century naturalists did in their quest to catalogue species. Footnote 22 Rather than working with texts from the inside out, connecting them with what was known about the world at large, readers of Mendel worked from the outside in, trying to pin down the essence of what Mendel had to say.

This focus of attention may seem to point to a partisan attitude. Yet a closer consideration of the passages that were emphasized through underlining and marginal reading marks points toward a different explanation. Most copies we inspected demonstrate readers’ attention to the first sections of the paper that explain the material used and its experimental arrangement, and then report the empirical findings in subsequent generations for mono-, di- and trihybrid crosses. The first two sections on ‘Selection of experimental plants’ and ‘Arrangement and order of the trials’ tended to be the most heavily annotated. For instance, a reader of an English translation of Mendel's paper printed in Bateson's Mendel's Principles of Heredity (1913, third edition) extensively underlined parts of Mendel's suggestions on how to avoid cross-fertilizations. Footnote 23 Mendel's statement that pure-bred plants possessing ‘constantly differing traits’ must be used for his hybridization experiments was almost universally highlighted. Footnote 24 Readers sometimes even put lines against apparently trifling, but practically significant, details, such as Mendel's warning that the green colouration of the albumen sometimes is faint, making the peas appear yellow. This is true, for example, for the copy of Tschermak's 1901 edition of Mendel's paper that was likely annotated by the Danish geneticist Wilhelm Johannsen (1857–1927) shortly after it had appeared. Footnote 25 Such annotations, in conjunction with the lack of engagement with the more theoretical sections of Mendel's paper, indicate that, for many readers, this paper was mainly an instruction on how to conduct Mendelian experiments.

A final observation on the material we consulted lends additional support to this interpretation. As already mentioned, some readers dutifully noted the law of segregation and the law of independent assortment that look like Mendel's main contributions from today's perspective. These laws were formulated as empirical generalizations in the sections in which Mendel reported his findings from monohybrid and polyhybrid crosses. But even in this case, many readers exhibited more interest in the notation system and computational methods Mendel employed than in the actual empirical content of these generalizations. An excellent example is again provided by Johannsen, who would go on to become a central figure in classical genetics. Footnote 26 Johannsen added a long marginal note to the page on which Mendel formulated the following law (later called the law of independent assortment): ‘descendants of hybrids, in which several essentially different traits are united, represent the members of a combination series, in which the developmental series of two different traits respectively are conjoined’. Footnote 27 Mendel's formulation of the law was hardly transparent for readers who had yet to familiarize themselves with Mendelian combinatorics. In his marginal note, Johannsen therefore translated Mendel's verbal statement into mathematical form by multiplying the terms of two monohybrid series ( Figure 1 ). Mendel did not explicitly explain that ‘conjoining developmental series’ was supposed to imply this arithmetic operation. Johannsen, as a reader, had to try this out in order to get a clearer understanding of what Mendel's ‘law valid for Pisum’ was supposed to mean and what its implications actually were. Footnote 28

Figure 1. (A) Annotation by Wilhelm Johannsen in Gregor Mendel's Versuche (1901), which an overly diligent librarian (we believe) tried to erase. The annotation begins with a multiplication of two monohybrid series ‘(A + a + 2Aa) (B + b + 2Bb) o.s.v.’ (the abbreviation ‘o.s.v.’ means ‘and so on’). (B) Detail. The rest of the annotation develops formulae that Mendel also discusses in the text. With kind permission of the Copenhagen University Library Frederiksberg, Call no. 80–33, p. 22.

Johannsen also furnishes us with one of the few examples in which a reader added critical comments to a Mendelian treatise. In 1905, he received a copy of Punnett's Mendelism (1905) ‘with the author's kind regards’, as noted on the flyleaf. Annotations by Johannsen in this copy are scarce, but he also received a copy of the third edition (1911) which he filled with corrections and critical remarks, for example by contradicting Punnett's presentation of inheritance of size in peas in terms of Bateson's presence–absence theory. Against Punnett's claim that ‘[a]ll peas are dwarf, but the tall is a dwarf plus a factor which turns it into tall’, Johannsen placed the dry (and, from the present point of view, correct) remark: ‘No, it is [the] phenotype [of a] pure tall’. Footnote 29

Disagreements about how to interpret phenomena correctly are therefore not completely absent from the material we have investigated, but they remain a minority among the annotations we found. Moreover, one should not forget that Punnett's Mendelism , just like Bateson's Mendel's Principles of Heredity , was published in the polemical context of the debate between biometricians and Mendelians. Footnote 30 In the majority of annotated books that we have looked at, readers exhibited an interest in the details of concrete experimental procedures and their successful implementation. To achieve this success, computational procedures and the potential for visual display of intricate relationships through ‘paperwork’ were key elements, which we are going to follow up in the next two sections.

The art historian Martin Kemp has regarded Mendel's paper as a striking example of the paradoxical disappearance of ‘visual delights’ from natural history. As Kemp insists, Mendel must have possessed ‘[u]nrelenting visual and manual discipline’ to carry out his experiments with pea plants; and yet, he chose to present his results in the form of ‘rows of figures, with sets of paired characteristics designated by capital and lower-case letters’, thus demonstrating a pronounced lack of ‘illustrative interest.’ Kemp conjectured that ‘this shift away from the visual image’ was due to ‘a general sense that if natural history was to be regarded as a “hard” science, it needed to cast off its image as an attractive pursuit for amateurs and collectors of nature's wonders.’ Footnote 31

In our interpretation of Mendel's paper as a treatise in experimental design and applied mathematics, Kemp's paradox ceases to exist. Algebraic notations, ratios, tables and diagrams did not supersede the lavish illustrations of plants and animals familiar from natural history. They were the new visualizations required by an investigation of the laws of heredity that relied on combinatorial analysis. In Mendel's paper, algebraic, combinatorial and statistical computations became the key tools for representing the outcomes of artificial crossings and formulating expectations. In addition to gaining an understanding of the choices Mendel had made in the design of his experiments, readers therefore also had to acquaint themselves with the new visual realm that this notation system created on paper.

To acquire these skills, readers of Mendel's paper actively engaged with the text in two ways: by rehearsing calculations and by employing Mendel's notation system. Johannsen's copy of Tschermak's 1901 edition of Mendel's paper makes this engagement especially evident. Against a list of empirical results from a dihybrid cross in Mendel's paper, Johannsen placed the ratio 9:3:3:1 that was to be expected from the law of independent assortment and that fit well with Mendel's findings. In addition, however, he also noted the underlying 3:1 ratio of dominant to recessive traits for each of the individual character pairs ( Figure 2 ). He did so in an intriguing way, namely by drawing a line to connect the first and third rows of the column, which contained results for round seeds (315 and 108), and in this way also letting the second and fourth row stand out, which contained the results for angular seeds (101 and 32). The ratios noted next to the empirical numbers respectively (9:3 and 3:1) immediately made it clear that seeds differing by seed colour only segregated in a 3:1 ratio. Johannsen's annotation reveals how the visual arrangement of numerical data in tables served as a template for readers to perform operations and calculations that enhanced their understanding of the underlying combinatorial logic. Mendel himself had already arranged the table in such a way that it paired results for plants differing by seed shape only, and Johannsen seems to have tested the assumption that a corresponding rearrangement with a view on plants differing by seed colour only would yield the same result. Footnote 32

Figure 2. This table in Mendel's paper presents numerical results from a dihybrid crossing of peas with green ( grün ) and yellow ( gelb ) seed colour and angular ( kantig ) and round ( rund ) seed shape. On the left, Johannsen noted down the ratios corresponding to the empirical results (9:3:3:1). In addition, he connected the two lines giving results for round seeds. With kind permission of the Copenhagen University Library Frederiksberg, Call no. 80–33, p. 18.

In the same copy, there is another interesting example of Johannsen's engagement with computations. He dutifully examined a data table related to a trihybrid cross by drawing the sum for each column ( Figure 3 ). Repeating this computation was not really necessary to follow Mendel's argument, but evidently Johannsen wanted to get a better grasp of the unfamiliar procedure of data analysis and at the same time review the design of this trial that, in Mendel's own words, ‘asked for the most time and effort’. In addition, the sums represented the ratio between plants constant for all three characters, for two characters and for one character only. In the text of his paper, Mendel discussed this ratio in terms of averages calculated for each column, and it is possible that Johannsen also wanted to check these averages by drawing the sum for each column. Footnote 33

Figure 3. In this table included in Mendel's paper, Wilhelm Johannsen calculated the sums (noting ‘Sum’ in the margin) for the entries in each column (from left to right: 79, 228, 256; the first figure is wrong and should actually be 77). The table starts on the previous page, and only its lower half is shown in this reproduction. With kind permission of the Copenhagen University Library Frederiksberg, Call no. 80–33, p. 21.

Mendel's readers also familiarized themselves with the algebraic notation system Mendel used to represent his artificial crossings. Where Johannsen had annotated ratios, an anonymous reader of Mendel's original paper in the Brno Naturalists’ Associations’ journal placed combinations of upper-case and lower-case letters to represent the combinations of dominant and recessive characters according to Mendel's notation system. No real information is added to Mendel's text by this note, so it is plausible that the reader simply practised how to apply the notation system. Small inconsistencies indicate that he was still in the process of learning its use. Footnote 34

Attention to algebraic formalism can also be traced in the English translations of Mendel's paper. For instance, the translation printed in Bateson's first edition of Mendel's Principles of Heredity (1902) contained a typo in the table representing results from a trihybrid crossing that we discussed above. The typo was mentioned in the errata list at the beginning of the volume, and a copy from the private library of marine biologist Edwin Grant Conklin (1863–1952) has a correction of the misprint on the required page. Evidently, the mistake was amended because Mendel's formalism mattered to the reader of this early genetics textbook. The fact that the annotator did not realize at first that the erratum itself introduced another mistake suggests, on the other hand, that it took effort for readers to become familiar with Mendel's notation system. Footnote 35 A complicating factor is that Bateson's book inaugurated the transition from ‘Mendel's algebra’, which used single letters to represent homozygous trait combinations, to the standard algebra of classical genetics we are familiar with. The change is not just a matter of convention. Mendel's notation was developed without the concept of gene and allele, and Bateson was the first to point out the serious limitations of his formalism. Footnote 36

Shifting our attention to early introductions to genetics that built on Mendel's work, we came across many examples of readers’ engagement with computations. In his personal copy of the third edition of Punnett's Mendelism , for instance, which we already mentioned above for its polemical annotations, Johannsen computed the first six terms of the series 2 n and 3 n and wrote the results in the upper left-hand corner of the page. Johannsen was not repeating computations already made by Punnett. He was ‘testing figures’ for the number of possible forms arising when homozygous and heterozygous conditions are indistinguishable and distinguishable, as the arrangement of numbers suggests, probably to get an impression of how rapidly they were increasing with each added character pair. Footnote 37

Readers also had a very keen eye for detecting mistakes in the early genetics manuals that they studied. An anonymous reader of the second edition of Wilhelm Johannsen's textbook Elemente der exakten Erblichkeitslehre (1913) did not miss the wrong result of a multiplication. Johannsen's Elemente is renowned for introducing the words ‘gene’, ‘genotype’ and ‘phenotype’ to the biological lexicon, but the book was also an attempt to reconcile the mathematical achievements of the biometrical school with the latest findings of Mendelians. Footnote 38 The mistake must have been an oversight by the typesetter, because the final result of the summation that followed is correct, but the reader must have repeated the computation step by step in order to detect this mistake. Evidently, painstaking recalculation, even in cumbersome cases involving numerous steps, was an important reading practice by which mathematical procedures were internalized. Footnote 39

The readers of the early genetic textbooks we examined paid attention not only to arithmetic calculations, but also to the algebraic notation system that represented the crossings. One example is provided in a copy of an introductory textbook, Einführung in die experimentelle Vererbungslehre (Introduction to the Experimental Science of Heredity), that the leading German geneticist Erwin Baur (1875–1933) published in 1919. A reader amended a mistake in a tabular representation of results from a dihybrid crossing, where a dominant character had mistakenly been represented by a lower-case letter. This demonstrates once again that readers went to great lengths in double-checking, and hence internalizing, non-discursive, tabular, permutational or computational sections of the text. Footnote 40

The publication of R.A. Fisher's Statistical Methods for Research Workers in 1925 added a new set of tools to the computational baggage of genetics. Fisher was both a statistician and a geneticist, and his book, which was published in a series of biological monographs and manuals, had the ambition to explain the mathematical theory of statistical methods, ‘presenting them in the form of practical procedures appropriate to those types of data with which research workers are actually concerned’. Footnote 41 Statistical Methods for Research Workers was written for any experimental scientists who had to deal with statistical calculations, not just for geneticists. Yet, as one book reviewer remarked in the British Medical Journal (1926), due to the advanced statistical methods it presented, geneticists were singled out as a potentially more suitable audience. Footnote 42

Fisher gave geneticists new mathematical tools to facilitate the understanding of experimental design and related data analysis. In the analysis-of-variance method developed by Fisher, experimental results were displayed in a table, and subdivided by classes according to their cause of variation. This tabular arrangement made the structure of the experiment clearer and the arithmetic simpler. Footnote 43 In the preface to another textbook, The Design of Experiments , which was conceived as a practical guide to planning scientific experiments and analysing their results with suitable statistical methods, Fisher made it very clear that reading was not just an intellectual, but an eminently practical, exercise:

The reader is … advised that the detailed working of numerical examples is essential to a thorough grasp, not only of the technique, but of the principles by which an experimental procedure may be judged to be satisfactory and effective. Footnote 44

In Fisher's pairing of experimental design and computational analysis, and in his suggestion to the reader to recompute numerical examples to become familiar with them, we see not only a reflection of Fisher's own ideas, but also his belonging to a tradition that we trace back to Mendel's paper. In this tradition, texts were designed as instruments to convey precisely that ‘[u]nrelenting visual and manual discipline’ that, as Kemp rightly suspected, supports Mendelian experimentation. Or as Jeffrey Skopek has put it in his study of the use of historical cases in early genetics textbooks, ‘figures and tables that were presented as part of the Mendelian case [were] used to inculcate the geneticists’ way of seeing’. Footnote 45 In the following section, we want to turn to the new visual culture of genetics that was promoted in this way.

‘Visual thinking’ in mathematics and its epistemological value have a long and controversial history ranging from enthusiastic acceptance by Immanuel Kant to sheer disdain from Bertrand Russell. Footnote 46 Images and diagrams have been employed in the proof of mathematical theorems; their value as tools for thinking and teaching aids has long been debated in mathematical research and education. Footnote 47 Occasionally, in the past three decades, the role of diagrams has also moved centre stage in the history and philosophy of science, including calls to consider their role in the modern life sciences. Footnote 48

In our own research on the annotated copies of Mendel's paper and early genetics manuals, visualizations emerged as a key tool in conveying and learning about experimental practices of artificial crossings and related combinatorial operations. Mendel's original paper already contained a diagram that connected pollen and egg cells (symbolized by upper-case and lower-case letters) with arrows to illustrate the combinations that resulted from their random union. This diagram summarized Mendel's speculations about the mechanism that could explain segregation patterns. At the same time, it suggested a basic procedure by which readers could visualize the combinatorial logic underlying artificial cross-fertilizations and intuitively derive the segregation ratios simply by connecting two series of terms by lines. Footnote 49

In the previous section we already came across one example, in which a reader took up this suggestion ( Figure 2 ), and we want to add another example from the same copy of Mendel's paper. Two pages before the diagram, where Mendel derived the possible combinations of factors resulting from dihybrid back-crossing experiments, Johannsen used lines to connect the letters that Mendel had used in order to represent different kinds of germ and pollen cells. The lines do not exhaust all possible connections, but identify some chief components of the resulting combination series. Footnote 50 While not a prominent feature, we encountered a few other instances in which readers visualized the mechanism that generated combinatorial series. Footnote 51 It should also be noted that Mendel arranged his ‘developmental series’ very consciously in a way that allowed readers to visually explore patterns and symmetries. Footnote 52

A particularly interesting case is presented in notes that the Swedish plant breeder Herman Nilsson-Ehle (1873–1949) entered on the back flyleaf of his personal copy of Tschermak's Mendel edition. He probably received the copy from Tschermak himself, who in 1901 visited the Plant Breeding Station in Svalöf (Sweden). Footnote 53 On the rear flyleaf of his copy, Nilsson-Ehle tried in vain to solve a problem that any student of genetics would consider trivial today. Footnote 54 The upper half of the page is taken up by three representations of monohybrid crosses, two of them back crosses (AA × Aa and aa × Aa), for which Nilsson-Ehle correctly derives the phenotypic segregation ratios by employing diagrams that structurally resemble the diagram in Mendel's paper. The lower half seems to be a failed attempt at doing the same for a dihybrid cross. In a first attempt at the problem, Nilsson-Ehle tried to find a solution by simply placing diagrams for back crosses (Aa × AA and Bb × BB) next to each other, but he erased this attempt. In what follows, he connected one bifactorial term (AB and ab respectively) through lines with a series of four other terms (AB, Ab, aB, ab). The erasures and repeated attempts are a clear sign of the difficulties he experienced in reproducing the terms of the series for a dihybrid cross.

Nilsson-Ehle was experimenting with a visual arrangement that would become very popular in Mendelian genetics. The lower half of his notes comes close to what is known as the ‘Punnett square’, in which the genetic constitutions for male and female gametes, designated by Mendelian letters, form a matrix of rows and columns that allows one to predict the genetic constitution of the zygotes formed by their union in fertilization, as well as the probability of their occurrence in a large population. In addition, the fields in a Punnett square could be shaded and coloured for the resulting phenotype, thus making expected segregation ratios immediately intuitive, due to their symmetry of distribution. Punnett introduced this square diagram to the literature in 1906 in a paper co-authored with Bateson and Edith R. Saunders, and included it in the second edition of his Mendelism . In the third edition (1911), he added a verbal description of how to construct the diagram, and the Punnett square became a standard feature of Mendelian literature. As a detailed reconstruction by A.W.F. Edwards has shown, the diagram first took shape in an exchange of letters between Bateson and Galton for the more complex case of a trihybrid cross, and may well have been inspired by the way in which Mendel presented a case of trifactorial inheritance of flower colour in beans. Footnote 55

Readers’ annotations suggest that Punnett squares were not immediately obvious representations, but continued to rely on the interplay between text and image. Wilhelm Johannsen provides an example of the effort it took to connect textual explanations of Mendelian inheritance with the related combinatorics. In the third edition of Mendelism , Punnett resorted to one of his squares to explain colour inheritance in poultry. To grasp Punnett's explanation, Johannsen again used lines joining symbolic representations of allelic combinations in the text with respective fields in the diagram. When reading this text, Johannsen was certainly not a beginner in the study of inheritance. The first edition of his Elemente (1909) was not a book which refrained from the use of mathematical formalism. Yet even Johannsen had to rely on visualizations to intuit the expected outcomes of complex crosses and to reach a critical awareness of the basis on which an author built his argument. Footnote 56

In another case, a copy of Baur's Einführung that we already mentioned in the previous section, the reader made sense of an eight-by-eight Punnett's square both by annotating the book page and by listing possible phenotypic outcomes on a separate sheet of paper, which was then left in the book. Even though the Punnett square gave a complete list of all the possible genotypes, the reader obviously felt the need to complement it in various ways. Thus he corrected the table for some obvious typos, added the gametic genotype for each row, and marked the fields with a symbol system for resulting phenotype. It is unlikely that this reader was engaged in precisely the same experiment that Baur described, but he reviewed it in excruciating detail to better understand its underlying visual logic ( Figure 4 ). Footnote 57

Figure 4. (A) A Punnett square from Baur's Einführung (1919) and (B) an autograph sheet inserted in the book by a reader. While Punnett's square offers an efficient tool to present all possible combinations, the reader's list summarizes them in terms of their phenotypic outcome and groups them according to similarity. With kind permission of the Library of the Botanic Garden and Botanical Museum Berlin, Call no. 575 Bau <4>.

The Punnett square was not the only way to illustrate combinatorics in the early genetics manuals we examined. One of Mendel's rediscoverers, Carl Correns, preferred bifurcating diagrams. Footnote 58 In his second edition of Mendelism (1907), Punnett himself included a diagram – alongside his eponymous square – that illustrated the basic combinatorial events in gamete formation and fertilization in a form visually resembling a pedigree. These diagrams provided information on multiple generations and on the inheritance of genetic factors, and offered a summary of the crossing process at a glance. Their lines and arrows, circles and squares contributed to establish the visual language of the newly born genetics, alongside the tables, algebraic letters and ratios we have so far examined. Footnote 59

In addition, many of the early genetics manuals did not disdain colour plates in the tradition of natural-history publications. Beautiful colour plates and photographs are displayed in Bateson's, Baur's, Punnett's and Castle's textbooks. Through these plates, plants and animals (peas, primulas, snapdragons, maize, butterflies, fowls, mice, rabbits and more) and the laws that governed the inheritance of colour and other visible traits were revealed to the reader. This rich iconography was a helpful learning tool only for the engaged reader who went from text to image, from image to computation, and from computation back to text and image to fully understand the crossings described, as sometimes is evident from readers’ annotations on the plates. Footnote 60 Thus, with Kemp, one should not consider these illustrations as a mere survival from the natural-history tradition. While similar in their aesthetics, they were permeated by the very same combinatorial logic that the texts and diagrams in the books they illustrated tried to convey to their readers.

As mentioned in the introduction, the reception of Mendel's paper remains poorly understood. The mathematical knowledge required by the reader has been considered a potential stumbling block in its reception, because it was ‘forbidding to an audience interested in hybridization’. Footnote 61 Yet our findings point in the opposite direction. Tangible marks of active engagement – such as calculation of intermediate steps in long computations and correction of typos in numeric figures and algebraic letters – are abundant in the more mathematical sections of Mendel's paper and of genetics textbooks published in the early decades of the twentieth century. Mathematical knowledge was accessible even to the uninitiated by directly engaging with tabular arrangements and calculations in the text. The readers of Mendel's paper and Mendelian introductions to genetics did not skip these technical sections, but worked through them thoroughly. Even though biologists have often been portrayed as shy of mathematics, we gather from our sample of annotated copies that the students and researchers who read these texts accepted statistical methods and experimental design as part and parcel of their work, alongside the observations conducted at the lab bench and in the experimental garden. While it is true that the computing equipment in biological research was always limited in the early decades of the twentieth century – pen, paper, mathematical tables, slide rules and only occasionally a calculating machine – and while it is also true that biologists hardly considered their work ‘computational’ at this stage, genetics was beginning to acquire computational aspects back then.

According to philosopher Charles Saunders Peirce, ‘all deductive reasoning, even simple syllogism, involves … constructing an icon or diagram … experimenting upon this image in the imagination, and … observing the result so as to discover unnoticed and hidden relations among the parts’. Footnote 62 This also means that reasoning needs to be practised, even on basic levels that more than a century later seem utterly trivial. Our foray into readers’ annotations has revealed that both the authors of Mendelian texts and their readers were aware of this, and that these texts were designed and used in accordance with this design, to facilitate the profoundly visual and manual discipline needed to carry out genetic experiments. From our findings, it is evident that reading was not confined to the linear order of words in sentences, or of sentences in arguments. It also took note of the two-dimensional arrangement of words, numbers and symbols in series, tables and diagrams.

For the topic of this issue, ‘learning by the book’, there is a corollary from these findings. It may be futile to try to define the ‘manual’ or ‘handbook’ as a genre since whether a text is read to gain practical knowledge depends at least as much on how readers engage with it as it does on the motivations that guided its author(s) in writing it. Mendel's paper was meant to report empirical results from a series of experiments when it was originally published in 1866 and to suggest an explanation for these results, but it became a manual, or protocol, for conducting Mendelian experiments after its ‘rediscovery’ in 1900.

Acknowledgements

Staffan Müller-Wille would like to acknowledge support from the Swiss National Foundation Sinergia Grant CRSII5_183567, In the Shadow of the Tree: The Diagrammatics of Relatedness as Scientific, Scholarly, and Popular Practice. Giuditta Parolini is grateful to the German Research Foundation (DFG) for the funding received since 2017 (grant no. 321660352). Both authors would like to thank the issue editors and all the other participants in the workshops on Learning by the Book in Princeton and Berlin for asking challenging questions and forcing them to sharpen their focus.

Supplementary material

The supplementary material for this article can be found at https://doi.org/10.1017/bjt.2020.12

1 Mendel , Gregor , Versuche über Pflanzenhybriden: Zwei Abhandlungen, 1865 und 1869 (ed. Tschermak , Erich. v. ) (Ostwalds Klassiker der exakten Wissenschaften, vol. 121), Leipzig : Wilhelm Engelmann , 1901 Google Scholar ; Mendel , Gregor , ‘ Experiments in plant hybridisation, with an introductory note by W. Bateson, M.A., F.R.S. ’, Journal of the Royal Horticultural Society ( 1901 ) 26, pp. 1 – 32 Google Scholar .

2 Malpighi , Marcello , Die Anatomie der Pflanzen (ed. Möbius , M. ) (Ostwalds Klassiker der exakten Wissenschaften, vol. 120), Leipzig : Wilhelm Engelmann , 1901 Google Scholar ; Gauss , Carl Friedrich , Sechs Beweise des Fundamentaltheorems über quadratische Reste (ed. M. Möbius) (Ostwalds Klassiker der exakten Wissenschaften, vol. 122), Leipzig : Wilhelm Engelmann , 1901 Google Scholar .

3 Radick , Gregory , the , ‘Beyond “ Mendel–Fisher controversy ”’, Science ( 2015 ) 350 ( 6257 ), pp. 159 –60 CrossRef Google Scholar PubMed .

4 Allen , Garland E. , ‘ The classical gene: its nature and its legacy ’, in Parker , Lisa S. and Ankeny , Rachel A. (eds.), Mutating Concepts, Evolving Disciplines: Genetics, Medicine and Society , Dordrecht : Kluwer Academic , 2002 , pp. 11 – 42 CrossRef Google Scholar .

5 Darden , Lindley , Theory Change in Science: Strategies from Mendelian Genetics , Oxford : Oxford University Press , 1991 Google Scholar ; Kim , Kyung-Man , Explaining Scientific Consensus: The Case of Mendelian Genetics , New York : Guilford Press , 1994 Google Scholar .

6 Paul , Diane B. and Kimmelman , Barbara A. , ‘ Mendel in America: theory and practice 1900–1919 ’, in Benson , Keith , Maienschein , Jane and Rainger , Ronald (eds.), The American Development of Biology , Philadelphia : University of Pennsylvania Press , 1988 , pp. 281 – 310 Google Scholar .

7 A history of the concept of gametic purity is outstanding. It was advertised as the ‘essence’ of Mendelism by William Bateson; see Radick , Gregory , ‘ Other histories, other biologies ’, Royal Institute of Philosophy Supplements ( 2005 ) 56 , pp. 21 – 47 CrossRef Google Scholar , 38.

8 Rheinberger , Hans-Jörg and Müller-Wille , Staffan , The Gene: From Genetics to Postgenomics , Chicago : The University of Chicago Press , 2012 , pp. 28 – 33 Google Scholar .

9 Wimsatt , William C. , ‘ The analytic geometry of genetics: Part I: the structure, function, and early evolution of Punnett squares ’, Archive for History of Exact Sciences ( 2012 ) 66 , pp. 359 –96, 359 CrossRef Google Scholar .

10 A CSV file with data on the book copies we consulted is available as supplementary material with the online version of this article. In addition, we provide access to supplementary material in the form of a Microsoft Word document that includes more detailed bibliographic information (Appendix I), and some additional images (Appendix II).

11 We have not checked copies of the countless short journal articles that were produced by many Mendelians in the first decade of the twentieth century to popularize Mendelism. For a short discussion of these articles see Staffan Müller-Wille and Martha Richmond, ‘Revisiting the origin of genetics’, in Staffan Müller-Wille and Christina Brandt (eds.), Heredity Explored: Between Public Domain and Experimental Science, 1850–1930 , Cambridge, MA: MIT Press, 2016, pp. 367–94, 368. See also Mike Buttolph, ‘One hundred and one Mendelians’, MSc dissertation, London Centre for History of Science, Medicine and Technology, 2008, at https://profjoecain.net/one-hundred-and-one-mendelians-buttolph-2008/ (accessed 21 October 2020).

12 For recent reviews of this literature see Ann M. Blair, ‘The rise of note-taking in early modern Europe’, Intellectual History Review (2010) 20, pp. 303–16; Isabelle Charmantier and Staffan Müller-Wille, ‘Worlds of paper: an introduction’, Early Science and Medicine (2014) 19, pp. 379–97; Boris Jardine, ‘State of the field: paper tools’, Studies in History and Philosophy of Science Part A (2017) 64, pp. 53–63.

13 On the historiography of Mendel see Staffan Müller-Wille, ‘Gregor Mendel and the history of heredity’, in Michael R. Dietrich, Mark Borello and Oren Harman (eds.), The Historiography of Biology , New York: Springer 2018, at https://doi.org/10.1007/978-3-319-74456-8_8-1 .

14 One of the few studies that comes to mind is David Kaiser's book on the historical development of Feynman diagrams. Kaiser argues that the use of these diagrams was practised in direct, personal interaction with instructors, whereas our material indicates that some geneticists, at least, learned to use Mendel's notation system while actively engaging with texts alone. Cf. Kaiser , David , Drawing Theories Apart: The Dispersion of Feynman Diagrams in Postwar Physics , Chicago : The University of Chicago Press , 2009 , p. 110 Google Scholar .

15 Wilhelm Ostwald, Lebenslinien: Eine Selbstbiographie , 3 vols., Berlin: Klasing, vol. 2, p. 55. On the publication history of the series see Lothar Dunsch and Hella Müller (eds.), Ein Fundament zum Gebäude der Wissenschaften: Einhundert Jahre Ostwalds Klassiker der exakten Wissenschaften , Leipzig: Geest and Portig, 1989. Translations, if not otherwise indicated, are our own.

16 See Appendix I in the supplementary material for a list of the ‘manuals’ we consulted for this article.

17 The only exception is a 1917 facsimile edition of Mendel's paper as it was originally published in the Brno Naturalists’ Association journal. In this case a reader underlined the expression bildungsfähige Elemente (‘elements capable of development’) in the original from which the facsimile was produced. We cannot exclude the possibility that the annotation pre-dates the ‘rediscovery’ of Mendel in 1900. See Gregor Mendel, Versuche über Pflanzen-Hybriden: Brünn 1866 (facsimile edn, ed. W. Junk, No. 20), Berlin: W. Junk, 1917 (Staatsbibliothek Berlin, call no. Ag 213–20), p. 42.

18 Gregor Mendel, Versuche über Pflanzenhybriden: Zwei Abhandlungen, 1865 und 1869 (ed. Erich Tschermak) (Ostwalds Klassiker der exakten Wissenschaften, vol. 121), Leipzig: Wilhelm Engelmann, 1901, Library of the Botanic Garden and Botanical Museum Berlin, call no. GE 20, pp. 6, 10, 16; see Appendix II, Figure 1 in the supplementary material for a reproduction. The copy has an owner stamp, ‘Joseph Mendel’, on its first page, but we were not able to establish who Joseph Mendel was.

19 For example, in Mendel, op. cit. (18), Staatsbibliothek Berlin, call no. Ae5750, p. 28, a vertical line is placed next to the derivation of the ‘law of independent assortment’ running down the entire page. In Gregor Mendel, Experiments in Plant-Hybridisation , Cambridge, MA: Harvard University Press, 1926 (Princeton University Library, call no. QK841.M5313), pp. 321, 323, a reader placed marginal ticks against the law of uniformity and another formulation of the 3:1 ratio.

20 Ann M. Blair, Too Much to Know: Managing Scholarly Information before the Modern Age , New Haven, CT: Yale University Press, 2010.

21 Renée Raphael, Reading Galileo: Scribal Technologies and the Two New Sciences , Baltimore: Johns Hopkins University Press, 2017.

22 Müller-Wille , Staffan and Charmantier , Isabelle , ‘ Natural history and information overload: the case of Linnaeus ’, Studies in History and Philosophy of Biological and Biomedical Sciences ( 2012 ) 43 , pp. 4 – 15 CrossRef Google Scholar PubMed ; Dietz , Bettina , ‘ Making natural history: doing the Enlightenment ’, Central European History ( 2010 ) 43 , pp. 25 – 46 CrossRef Google Scholar .

23 Gregor Mendel, ‘Experiments in plant hybridization’, in William Bateson, Mendel's Principles of Heredity , Cambridge: Cambridge University Press, 1913, University of Toronto, Gerstein Science Information Centre, p. 337 (Biodiversity Heritage Library, at www.biodiversitylibrary.org/item/61163#page/389/mode/1up , accessed 16 October 2019).

24 For example, Mendel, op. cit. (18), Library of the Botanic Garden and Botanical Museum Berlin, call no. GE 20, and Staatsbibliothek Berlin, call no. Ae5750, p. 4; Gregor Mendel, ‘Experiments in plant hybridization’, in William Bateson, Mendel's Principles of Heredity , Cambridge: Cambridge University Press, 1902, Library of the Marine Biological Laboratory, Woods Hole, call no. QH431.B312, p. 42 (Biodiversity Heritage Library, at www.biodiversitylibrary.org/item/16926#page/66/mode/1up , accessed 16 October 2019).

25 Mendel, op. cit. (18), Science Library of the University of Copenhagen, call no. 80–33, p. 13. The title page bears a stamp, ‘Kgl Veterinær- og Landbohøjskoles Bibliotek’. Johannsen worked for the Royal Veterinary and Agricultural College in Copenhagen from 1892 to 1905 and his notes do not yet use the modern notation that Bateson popularized in 1902. Moreover, although the writing is very small and difficult to read, there are a few verbal notes in this copy that seem to be in Johannsen's hand. The same sentence was marked by the reader of Mendel, op. cit. (18), Staatsbibliothek Berlin, call no. Ae5750, p. 13.

26 On Johannsen's contributions to the history of genetics see Nils Roll-Hansen, ‘The crucial experiment of Wilhelm Johannsen’, Biology and Philosophy (1989) 4, pp. 303–29.

27 English translation cited from Gregor Mendel, ‘Experiments on plant hybrids’ (1866), translation and commentary by Staffan Müller-Wille and Kersten Hall, BSHS Translation Series, at www.bshs.org.uk/bshs-translations/mendel .

28 Mendel, op. cit. (18), Science Library of the University of Copenhagen, call no. 80–33, p. 22.

29 Reginald C. Punnett, Mendelism , 3rd edn, London: MacMillan, 1911, Royal Library Copenhagen, call no. 8° N. hist. 20481, p. 31; see Appendix II, Figure 2 in the supplementary material for a reproduction. Another marginal note beginning with ‘No …’ can be found on another page (p. 130), and Punnett's discussion of how Mendelism solves practical problems in plant breeding is annotated with a question mark (p. 151). The title page of this copy is stamped ‘Wilhelm Johannsen's samling’ and dated ‘12/11/11’.

30 Bateson's Mendel's Principles of Heredity provides us with another example of a critical reader. In June 1902, Tschermak received a copy from the author, as noted on the flyleaf, and added extensive comments to the section of the book in which Bateson interpreted Mendel's experiments. Against Bateson's claim that Mendel made ‘no prediction as to the outward and visible characters of AB ’, Tschermak wrote: ‘Na! Na!’, a German way of expressing admonishment. William Bateson, Mendel's Principles of Heredity: A Defence , London: Clay, 1902, Library of the John Innes Centre, p. 24.

31 Kemp , Martin , ‘ Peas without pictures: Gregor Mendel and the mathematical birth of modern genetics ’, Nature ( 2002 ) 417 , p. 490 Google Scholar .

32 Mendel, op. cit. (18), Science Library of the University of Copenhagen, call no. 80–33, p. 18.

33 Mendel, op. cit. (18), Science Library of the University of Copenhagen, call no. 80–33, p. 21.

34 Mendel, op. cit. (17), p. 19; see Appendix II, Figure 3 in the supplementary material for a reproduction.

35 Bateson, op. cit. (30), Library of Marine Biological Laboratory, Woods Hole, call no. QH431.B22, p. 63 (Biodiversity Heritage Library, at www.biodiversitylibrary.org/item/16926#page/87/mode/1up ). The copy bears a stamp ‘Private Library Edwin Conklin’ on the front flyleaf. The errata list erroneously asks the reader to replace the upper-case ‘C’ in the printed formula ‘AabbC’ with a lower-case ‘c’. The reader copied the formula as advised by the errata list, and only then changed the formula to the correct ‘AaBbC’.

36 Gayon , Jean , ‘ From Mendel to epigenetics: history of genetics ’, Comptes rendus: Biologies ( 2016 ) 339 , pp. 225 –30 CrossRef Google Scholar PubMed , 226. Bateson added a footnote to Mendel's paper in his 1902 translation and discussed Mendel's way of symbolizing compound traits in Phaseolus multiflorus . Conklin's copy has a vertical line marked in the margin of this passage. See Bateson, op. cit. (30), Library of Marine Biological Laboratory, Woods Hole, call no. QH431.B22, p. 80. On Mendel's notation system see Robert C. Olby, ‘Mendel no Mendelian?’, History of Science (1979) 17, pp. 53–72, 58–62.

37 Punnett, op. cit. (29), Royal Library Copenhagen, call no. 8° N. hist. 20481, p. 126; see Appendix II, Figure 4 in the supplementary material for a reproduction.

38 Müller-Wille and Richmond, op. cit. (11), pp. 379–80.

39 Wilhelm Johannsen, Elemente der exakten Erblichkeitslehre , 2nd edn, Jena: Gustav Fischer, 1913, Staatsbibliothek Berlin, call no. La1983(2), p. 51. For a reproduction of the correction see Staffan Müller-Wille and Giuditta Parolini, ‘Punnett squares and hybrid crosses: how Mendelians learned their trade by the book’, History of Knowledge Blog , 2018, https://historyofknowledge.net/2018/05/08/punnett-squares-and-hybrid-crosses , accessed 16 October 2019.

40 Erwin Baur, Einführung in die experimentelle Vererbungslehre , 3rd edn, Berlin: Borntraeger, 1919, Library of the Botanic Garden and Botanical Museum Berlin, call no. 575 Bau <4>, p. 93; see Appendix II, Figure 5 in the supplementary material for a reproduction.

41 Ronald A. Fisher, Statistical Methods for Research Workers , 5th edn, Edinburgh: Oliver and Boyd, 1934, p. ix.

42 Anonymous , ‘ Statistical methods for research workers [book review] ’, British Medical Journal ( 1926 ) 1 ( 3404 ), pp. 578 –9 Google Scholar .

43 Parolini , Giuditta , ‘ The emergence of modern statistics in agricultural science: analysis of variance, experimental design and the reshaping of research at Rothamsted Experimental Station, 1919–1933 ’, Journal of the History of Biology ( 2015 ) 48 , pp. 301 –35 CrossRef Google Scholar PubMed .

44 Ronald A. Fisher, The Design of Experiments , Edinburgh: Oliver and Boyd, 1935, p. vi.

45 Skopek , Jeffrey M. , ‘ Principles, exemplars, and uses of history in early 20th century genetics ’, Studies in History and Philosophy of Biological and Biomedical Sciences ( 2011 ) 42 , pp. 210 –25 CrossRef Google Scholar PubMed , 214.

46 Marcus Giaquinto, ‘Visualizing in mathematics’, in Paolo Mancosu (ed.), The Philosophy of Mathematical Practice , New York: Oxford University Press, 2011, pp. 22–45.

47 Paolo Mancosu, Klaus Frovin Jørgensen and Stig Andur Pedersen (eds.), Visualization, Explanation and Reasoning Styles in Mathematics , Dordrecht: Springer Netherlands, 2005; Paolo Mancosu (ed.), The Philosophy of Mathematical Practice , New York: Oxford University Press, 2011.

48 James R. Griesemer and William C. Wimsatt, ‘Picturing Weismannism: a case study in conceptual evolution’, in Michael Ruse (ed.), What Philosophy of Biology Is: Essays Dedicated to David Hull , The Hague: Martinus-Nijhoff, 1989, pp. 75–137; Wimsatt, op. cit. (9); William Bechtel, ‘Understanding biological mechanisms: using illustrations from circadian rhythm research’, in Kostas Kampourakis (ed.), The Philosophy of Biology: A Companion for Educators , New York: Springer, 2013, pp. 487–510. On diagrams from a history-of-science perspective see Smets , Alexis and Lüthy , Christoph , ‘ Words, lines, diagrams, images: towards a history of scientific imagery ’, Early Science and Medicine ( 2009 ) 14 , pp. 398 – 439 CrossRef Google Scholar ; and Charlotte Bigg, ‘Diagrams’, in Bernard Lightman (ed.), A Companion to the History of Science , Hoboken, NJ: Wiley, 2016, pp. 557–68.

49 Mendel , Gregor , ‘ Versuche über Pflanzen-Hybriden ’, Verhandlungen des Naturforschenden Vereines zu Brünn ( 1866 ) 4 , pp. 3 – 47 Google Scholar , 30. For the diagram and a short discussion of its multi-layered meaning see Müller-Wille and Hall, op. cit. (27), commentary on p. 30, s. 1 (at www.bshs.org.uk/bshs-translations/mendel/2016?page=30&sentence=1 , accessed 16 October 2019).

50 Mendel, op. cit. (18), Science Library of the University of Copenhagen, call no. 80–33, p. 28; see Appendix II, Figure 6 in the supplementary material for a reproduction.

51 For example Mendel, op. cit. (17), p. 20.

52 Müller-Wille and Hall, op. cit. (27), commentary on p. 31, s. 7 (at www.bshs.org.uk/bshs-translations/mendel/2016?page=31&sentence=7 , accessed 16 October 2019).

53 Staffan Müller-Wille, ‘Hybrids, pure cultures, and pure lines: from nineteenth-century biology to twentieth-century genetics’, Studies in History and Philosophy of Biological and Biomedical Sciences (2007) 38, pp. 796–806.

54 Mendel, op. cit. (18), Library of the Plant Breeding Station Svalöf (current location unknown). On Nilsson-Ehle and plant breeding in Svalöf see Müller-Wille , Staffan , ‘ Early Mendelism and the subversion of taxonomy: epistemological obstacles as institutions ’, Studies in History and Philosophy of Biological and Biomedical Sciences ( 2005 ) 36 , pp. 465 –87 CrossRef Google Scholar PubMed . See Appendix II, Figure 7 in the supplementary material for a reproduction.

55 Edwards , A.W.F. , ‘ Punnett's square ’, Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences ( 2012 ) 43 , pp. 219 –24 CrossRef Google Scholar PubMed ; and Edwards , , ‘ Punnett's square: a postscript ’, Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences ( 2016 ) 57 , pp. 69 – 70 CrossRef Google Scholar . Wimsatt, op. cit. (9), p. 370, identifies a range of intrinsic properties of the Punnett square, such as decomposability, that explain its ‘truly remarkable’ spread, and provides a detailed account of its surprising diversity and complex evolution.

56 Punnett, op. cit. (29), Royal Library Copenhagen, call no. 8° N. hist. 20481, p. 118–19; see Appendix II, Figure 8 in the supplementary material for a reproduction.

57 Baur, op. cit. (40), Library of the Botanic Garden and Botanical Museum Berlin, call no. 575 Bau <4>, p. 86.

58 Rheinberger , Hans-Jörg , ‘ Eine Randnotiz zur Repräsentation von Generationen in Mendels Vererbungslehre ’, in Weigel , Sigrid , Parnes , Ohad , Vedder , Ulrike and Willer , Stefan (eds.), Generation: Zur Genealogie des Konzepts – Konzepte von Genealogie , Munich : Fink , 2005 , pp. 261 –6 Google Scholar .

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William Bateson (1861-1926)

At the turn of the twentieth century, William Bateson studied organismal variation and heredity of traits within the framework of evolutionary theory in England. Bateson applied Gregor Mendel's work to Charles Darwin's theory of evolution and coined the term genetics for a new biological discipline. By studying variation and advocating Mendelian genetics, Bateson furthered the field of genetics, encouraged the use of experimental methodology to study heredity, and contributed to later theories of genetic inheritance.

Bateson was born in Whitby, England on 8 August 1861 to parents Anna Aiken Bateson and William Henry Bateson, who was a classics scholar and Master of St. John's College at the University of Cambridge in Cambridge, England. Bateson had five siblings. Despite being described as vague and aimless by his grammar school headmaster at Rugby School in Rugby, England, Bateson entered St. John's College at Cambridge in 1879. Cambridge professors Adam Sedgwick and Walter Frank Raphael Weldon influenced Bateson as he studied embryology and anatomy. Bateson took first-class honors in the first part of the Cambridge final honors degree examination, the Natural Sciences Tripos, in 1882. A year later, Bateson sat the second part of the exam in zoology and received a first-class honors degree.

During the summers of 1883 and 1884, Bateson, on the advice of Sedgwick and Weldon, worked on a vertebrate ancestry project in the US. Bateson studied the morphology and embryology of the acorn worm Balanoglossus kowalevskii , (later called Saccoglossus kowalevskii ), under Johns Hopkins University zoologist William Keith Brooks at the Chesapeake Zoological Laboratory, which was located in Hampton, Virginia. Throughout their time together, Bateson observed Brooks's rejection of the traditional methods of comparative embryology and morphology to derive phylogenies, the evolutionary histories of a group of organisms. Brooks advocated that embryologists and morphologists who studied variation should use rigorous experimental methods. Influenced by Brooks's ideas, Bateson left embryological research and focused on the experimental study of variation and heredity.

After he returned to Cambridge in 1884, Bateson began publishing his research on Balanoglossus and was elected Fellow of St. John's College in 1885. He continued to examine variation of organismal traits as part of the link between environment and adaptation, and he spent more than a year conducting related fieldwork in Russia, Turkistan, and Egypt. Overall, Bateson spent much of his time at Cambridge, where he collected, organized, and analyzed organisms with abnormalities as well as species that exhibited discontinuities in variation, or did not show a continuous gradient of change between organisms within the species.

In 1894 Bateson published the findings in his first book, Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species . Bateson's book outlined discontinuities in variation that he had observed between species. For example, he explains that the male Lamellicorn beetle, Xylotrupes gideon , is found in two forms, long-horned or short-horned. The absence of males with horns of medium length meant that variation within that species was not continuous. In Materials for the Study of Variation , Bateson also debuted terms such as meristic to describe variation in the number of body parts, and homeotic to describe variation in the arrangement of body parts, after which scientists later named homeotic genes. Bateson's book also challenged Charles Darwin's theory of natural selection. Bateson argued that natural selection could not fully explain the origin of species. According to Darwin, natural selection caused species to evolve from other species via the gradual accumulation of small advantageous characters within the organisms of the evolving species. However, Bateson noted instances of discontinuous variation within species, an observation that strengthened his support of saltationism, as he argued that evolution may sometimes occur in large jumps, rather than through the gradual accumulation of differences.

Initially, Materials for the Study of Variation received criticism. Bateson's critics included his former mentor Weldon, who disagreed with the qualitative methods that Bateson had used to study variation. Further criticism came from those in the discipline of biometry, a school of thought that sought to explain evolution through statistical methods, and that relied upon the conception of continuous variation among organisms within a species. Despite the lack of support from biometricians, geneticist Reginald Crundall Punnett, who created the Punnett square and collaborated with Bateson at Cambridge, later deemed Bateson's book as a landmark in biological thought. After it was published in 1894, Bateson was elected as Fellow of the Royal Society in London, England. Bateson was involved with the Royal Society throughout the rest of his life, and he earned the Royal Society's Darwin Medal in 1904 and the Royal Medal in 1920.

With the rise of biometry, Bateson did not abandon his investigation of discontinuous variation, but he shifted his methodology from observational to laboratory experimentation. Many morphologists did not support Bateson's transition, so he turned to an underutilized resource for research assistance: women. Bateson initially worked with his sister, Anna Bateson, and later, Dorothea Pertz, both botanists trained at Newnham College, one of Cambridge's colleges for women. In 1895 Bateson began a series of cross-breeding and hybridization experiments with botanist Edith Rebecca Saunders. Bateson and Saunders's crosses of the flowering plant Biscutella laevigata exhibited discontinuous variation in the smoothness of leaves, so they expanded their work to include four other flowering plant species from genera Matthiola , Lychnis , Atropa , and Datura . Despite their extensive experiments, they could not distinguish any consistent pattern or mechanism of inheritance. Bateson expanded his work to include butterflies and poultry, but still could not fathom a mechanism until 1900, when Bateson and Saunders learned of Mendel's 1866 pea inheritance paper, which Mendel had written while in Austria.

Bateson adopted Mendel's work, and he advocated for others to do so. The majority of Bateson and Saunders's results from flowering plant crosses fit Mendel's laws of inheritance. In 1902 Bateson published Mendel's Principles of Heredity: A Defence , and Bateson's support of Mendelism rather than of biometry started an argument between Bateson and Weldon. This argument culminated in a debate in 1904, known as the biometric-Mendelian controversy, at the British Association for the Advancement of Science meeting at Cambridge. The debate involved Bateson and Karl Pearson, a colleague of Weldon's. Even though many scientists supported biometry rather than Mendelism, Bateson advocated for Mendel's theories, and he sought to expand upon Mendel's work through his own research.

During the first decade of the twentieth century, Bateson assembled a research group that included Punnett, who co-founded the Journal of Genetics with Bateson in 1910. Beatrice Durham, whom Bateson married in 1896, also assisted in the research, caring for research organisms and recording data. Bateson's team persisted even when Bateson left a genetics professorship at Cambridge in 1910 to be the first director of the John Innes Horticultural Institute in Merton, England. Throughout this time, Bateson and his colleagues made several discoveries in genetics and described various genetic phenomena. These included Bateson's definition of linkage, the tendency of genes that are located near each other to be inherited together; and epistasis, a type of gene interaction in which the expression of one gene can be activated or suppressed by another gene, though epistasis was first extensively described in 1907 by Muriel Wheldale Onslow, a member of Bateson's research group. Using crossbreeding and hybridization experiments, Bateson demonstrated that both plant and animal populations exhibit Mendelian principles. Bateson and Punnett also researched plant chimeras, single organisms that have two distinct genotypes.

In 1913 Bateson published his final book, Problems of Genetics , which discussed genetic phenomena and speciation. Bateson continued to study organisms with abnormalities and the problems of variation within the context of the origin of species. By this time, many biologists had accepted Mendel's theories. Bateson opposed chromosome theory, however, which held that genes were located on chromosomes. Chromosome theory had gained scientific support by 1910, yet Bateson found it difficult to reconcile Mendelian segregation and genetic linkage with the chromosome theory of inheritance. Toward the end of his life, Bateson came to partially accept chromosome theory, but he criticized what he perceived to be its inability to completely explain inheritance. Bateson remained director at the Horticultural Institute until his death at age sixty-four in 1926.

• Bateson, William. "The Early Stages in the Development of Balanoglossus (sp. incert.)." Quarterly Journal of Microscopical Science (1884): 206–236. http://jcs.biologists.org/content/s2-24/94/208.full.pdf (Accessed March 9, 2013).
• Bateson, William. "The Later Stages in the Development of Balanoglossus kowalevskii , with a suggestion as to the affinities of the Enteropneusta." Quarterly Journal of Microscopical Science 25 (Supplement) (1885): 81–122.
• Bateson, William. Materials for the Study of Variation Treated with Especial Regard to Discontinuity in the Origin of Species . London: Macmillan, 1894. http://www.biodiversitylibrary.org/item/61091 (Accessed March 9, 2013).
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• Hall, Brian K. "Betrayed by Balanoglossus : William Bateson's Rejection of Evolutionary Embryology as the Basis for Understanding Evolution." Journal of Experimental Zoology Part B: Molecular and Developmental Evolution 304B (2005): 1–17.
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• Mendel, Gregor Johann. “Versuche über Pflanzen-Hybriden” [Experiments Concerning Plant Hybrids].” Verhandlungen des naturforschenden Vereines in Brünn [Proceedings of the Natural History Society of Brünn] IV (1865): 3–47. Reprinted in Fundamenta Genetica , ed. Jaroslav Kříženecký, 15–56. Prague: Czech Academy of Sciences, 1966. http://www.mendelweb.org/Mendel.html (Accessed January 30, 2014).
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• v.18(10); 2022 Oct

Weldon, Bateson, and the origins of genetics: Reflections on the unraveling and rebuilding of a scientific community

Lea k. davis.

1 Division of Genetic Medicine, Department of Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America

2 Vanderbilt Genetics Institute, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America

3 Department of Psychiatry and Behavioral Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America

4 Department of Biomedical Informatics, Vanderbilt University Medical Center, Nashville, Tennessee, United States of America

5 Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America

“ Science , like most forms of human activity , is occasionally liable to lose sight of its ultimate ends under a flood of controversy , the strugglings of personal ambition , or the fight for pecuniary rewards or less physical honors … But science, no less than theology or philosophy , is the field for personal influence, for the creation of enthusiasm , and, for the establishment of ideals of self-discipline and self-development.”—Karl Pearson [ 1 ]

More than a century has passed since the publication of R.A. Fisher’s 1918 paper “The correlation between relatives on the supposition of mendelian inheritance”. Celebrated across the world as a major turning point in the young science of genetics, the paper formally reconciled mendelian and biometric approaches to inheritance by introducing the concepts of variance and polygenicity and laying the groundwork for the complex trait liability threshold model, which remains highly relevant to modern human genetics [ 2 ]. While many in the field of human genetics are aware of this work, few are aware of the controversy that preceded it. It is an origin story for the field of human genetics, filled with both drama and discovery. The lessons herein resonate today as we continue to contend with the trials of hyper-competitive incentive structures, a workaholic academic culture, and larger-than-life egos that often hide the vulnerability we feel as mere mortals tasked with tremendous feats.

Now is an opportune time to revisit these origin stories of our field. Given the magnitude of the problems facing us today, there is an urgent need for larger and larger scientific communities to function healthfully. Anyone who has felt in their gut the awe and humility of discovery understands that we are not entitled to learn the secrets of the Universe, we labor to gain even the smallest insight. Individually, we will be wrong far more often than we will be right. In this tale, what began as a scientific debate between friends devolved into a bitter argument, creating a chasm in the scientific community that persisted for decades and arguably stalled the progress that Fisher’s paper later spurred. In a sense, this story can be viewed as a “morality tale” about the dangers of competitiveness, the responsibility of influential voices, and the importance of maintaining a profound sense of humility as a scientist. The following centers the very elements that complicate healthy team science—friendship, ego, and ambition, and illustrates how they were weaponized in a war between scientists that was said to have resulted in at least 1 casualty [ 3 – 6 ]. It is my hope that by shining a spotlight on the interpersonal aspects of doing science, we may deepen our appreciation for the profound and enduring impact that our interactions can have on the scientific questions we choose to answer, the methods we adopt, and how we conceive of “ground truth.”

The story began long before Fisher was born, in 1859, with the publication of Charles Darwin’s book On the Origin of Species [ 7 ]. Darwin, privileged by wealth and education, traveled widely at an early age and compiled detailed notes on flora and fauna across the world. He gained an international reputation when he introduced the scientific world and the lay public to his theories of evolution and natural selection. Darwin’s half-cousin, Francis Galton, who was interested in similar ideas, had also recently published a book on his travels titled “Narrative of an explorer in tropical South Africa.” Despite a Royal Geographic Society review claiming the book was written with much “manly humor and style” [ 8 ], it was no comparison to Darwin’s thesis. After the publication of his cousin’s book, Galton (who later became known as the “father of eugenics”), focused his attention on questions pertaining to human variation, heredity, and selection provoked by Darwin’s theories of evolution. During his career, he formalized the statistical concepts of correlation and regression and his influence loomed large on all the personalities involved in the conflict to come.

Twenty years after the publication of Darwin’s book (1879), the 2 most important players in this drama, William Bateson (1861 to 1926) and Walter Frank Raphael Weldon (1860 to 1906), met as undergraduates at the University of Cambridge. Despite their different backgrounds, the two shared a common interest in zoology and both made his home in academia. Bateson, whose father was Master of St. John’s College (a constituent college of the University of Cambridge), was on track to attend Cambridge since childhood. In contrast, Weldon was the first in his family to attend a University, though his father Walter Weldon was a celebrated chemist and innovator [ 9 ]. Weldon quickly developed a reputation in the zoology department for being a clear and insightful teacher. During their years at Cambridge, a friendship grew, and though he was only 1 year older, Weldon became a peer mentor to Bateson.

By this time, the theory of evolution was widely accepted within scientific circles; however, the mechanisms through which new species arose remained a great mystery and was one of the most compelling scientific questions of the day. Bateson and Weldon were captivated and each set out to understand the process of speciation. Both men were also highly influenced by Galton’s work which, by then, had provided much of the foundation for modern statistics. Further, they were both personally acquainted with Galton and the three corresponded regularly. During the next decade, Bateson, Weldon, and Galton theorized widely on whether speciation was due to a slow and continuous process of selective breeding or could occur due to a major and rapid biological change (i.e., saltation).

Weldon and his wife Florence (nee Tebb) began collecting and studying wild populations of shrimps and crabs hoping to understand the relationship between continually varying morphological features within and between species. Weldon was quantitatively minded but lacked in computational skill [ 10 ]. Florence, who graduated from Girton College, Cambridge, was schooled in computation and a rigorous analyst. Together they collected, measured, and recorded dozens of anthropometric features on hundreds of samples, and Florence computed hundreds of descriptive statistics. Eventually, they sought a collaboration with Karl Pearson upon his joining the faculty of the University College London in 1892. It was their data on wild crab populations and questions about the continuous characteristics of these populations that provided Pearson both the means and motivation to develop the statistical methods for which he eventually became famous. Pearson once said, “Any mathematician could have done what I have done, a dozen or so better, especially if they had suggestions from Weldon almost daily at lunch for 4 or 5 years” [ 11 – 13 ]. Through years of painstaking data collection and analysis, the team eventually began to realize that anthropometric traits that distinguished different crab species also varied greatly within species. Indeed, upon the collection of enough data, even “dimorphic” traits appeared continuous. Thus, they came to believe that the most likely mechanism to explain evolution was slow and gradual natural selection.

Furthermore, Weldon believed the theoretical proof of this biological process could only be achieved through mathematics claiming that “The questions raised by the Darwinian hypothesis are purely statistical, and the statistical method is the only one at present obvious by which that hypothesis can be experimentally checked” [ 14 ]. This was not to say that he found no use for experimental data in uncovering potential mechanisms, only that he firmly believed in the necessity of statistical approaches to populations [ 15 ]. Nevertheless, this was not a popular opinion. As Pearson later remembered, “The very notion that the Darwinian theory might after all be capable of statistical demonstration seemed to excite all sorts and conditions of men to hostility. Weldon, instead of being allowed to do his own work in his own way, had to be constantly replying to letters, some even 18 sheets long … These letters were not sympathetic and suggestive, but mostly purely controversial,” [ 1 ]. Nevertheless, Pearson continued to work with Raphael and Florence Weldon and presented ideas that emerged from the crab populations including the concepts of standard deviation, covariance, and coefficient of variation [ 16 – 19 ]. It was also through Weldon that Pearson eventually met Galton. Galton became a life-long mentor and friend to Pearson and the two became so close that after Galton died, Pearson spent 20 years writing his definitive biography [ 20 ].

It should be noted that while Weldon believed in the necessity of statistical evidence to confirm observations, particularly in wild populations, he also valued laboratory experimentation and mechanistic understanding. In addition to his work on wild populations, he collaborated on breeding experiments using Japanese waltzing mice to evaluate segregation patterns in coat color, among other traits. Indeed, unpublished manuscripts (“ The Theory of Inheritance ”) written by Weldon in his later life [ 21 ] attempted to bring statistical and mechanistic insights gained through analysis of both wild populations and experimental studies together into a unified theory [ 15 , 21 ].

Meanwhile, Bateson worked diligently to perform carefully controlled experimental crosses of plant species in the Cambridge botanical gardens and frequently observed segregation of traits that clearly behaved as dimorphic (e.g., petal color). Based on these observations, he became convinced of the potential for “sporting mutations” (i.e., rare alleles with large phenotypic impacts) to drive evolutionary leaps. Bateson faced his own share of political pressure aimed at his theories and methods. The Director of the Morphological Laboratory at Cambridge, Adam Sedgwick, did not think highly of Bateson’s work. In a letter to his sister, Bateson confessed that “Sedgwick tells me he would not wish me to have Weldon’s lectureship if W. goes to University College. He says, as I expected, that I have gone too far afield and that my things are ‘a fancy subject’” [ 22 ].

The situation at Cambridge worsened for Bateson as he began expanding his research group. Bateson was sympathetic to the women’s suffrage movement in which his mother Anna Aitkin and sisters Margaret, Anna, and Mary Bateson were prominently involved ( Box 1 ). He welcomed women into his laboratory group. Some of the first papers from his group were coauthored by his sister Anna who also worked with Francis Darwin (botanist and son of Charles Darwin) during her studies at Cambridge. However, Sedgwick strongly disapproved of women in the academy, and this principled position cost Bateson throughout his career. Though he was employed at Cambridge for the entirety of his career, his promotion was overlooked for more than a decade. Nevertheless, his integrity remained intact and his collaborations with many female scientists including Edith Saunders, later referred to as the “mother of British plant genetics” [ 23 ], were incredibly productive ( Box 2 ).

Box 1. The price of feminism

We would be amiss to neglect the larger social context in which Weldon, Bateson, and their female colleagues were working. Women’s suffrage was a major political debate that impacted the career trajectory of men and women who supported women’s right to vote. In 1906, Mary Bateson was one of nearly a dozen women and men comprising a Women’s Suffrage Deputation who petitioned the Prime Minister from the floor of the House of Commons. Mary spoke on behalf of “women who are Doctors of letters, science, and law in the Universities of the United Kingdom and of the British Colonies ….who believe the disenfranchisement of one sex to be injurious to both and a national wrong in a country which pretends to be governed on a representative system”. (Women’s Suffrage Deputation, May 19, 1906; Received by the Prime Minister, Sir Henry Campbell-Bannerman, published by the National Union of Women’s Suffrage Societies, 25 Victoria Street, Westminster London, S.W.)

Box 2. Note on the important contribution of Edith Rebecca Saunders to the early discipline of genetics

Edith Rebecca Saunders was an influential early geneticist. Her experiments led to the characterization of the “allelomorph” (i.e., heterozygote and homozygote), many decades before Rosalind Franklin’s groundbreaking work characterizing the structure of DNA. She served as the Vice President of the Linnean Society, the 1920 President of the Botanical Section of the British Association for the Advancement of Science, and the 1938 President of the Genetical Society.

During these years, Weldon and Bateson corresponded often to debate the merits of gradual selection versus sporting mutation as well as the best methods of evaluation. In an 1888 letter, Weldon wrote to Bateson, “I have not written to you for a long time because I have the spirit of polemic upon me: and I have wished to consider carefully the words I should say to you. In the first place, I will tell you 3 sets of things which ought as it seems to me to annoy you …” He ended the letter lightheartedly by saying, “And when are you coming to crush me???” [ 6 ]. The friendly teasing in these correspondences foreshadowed the break that was to come.

In 1894, Bateson published the book “Materials for the study of variation treated with especial regard to discontinuity in the origin of species”. He presented the experimental crossing methodology that his team employed and used it to argue the case for the importance of saltation. Weldon was asked to write a critique of the book for Nature , and this seemed to mark the beginning of the public end to their friendship. While it was considered an overall positive review, he criticized Bateson’s thesis of evolution by saltation. Weldon was unimpressed by Bateson’s arguments stating “If the criticism and enunciation of opinions had been performed with the same care as the collection of facts, the commentary which runs through the book would have gained in value, and several inaccuracies, partly due to want of acquaintance with the history of the subject, would have been avoided” [ 24 ]. Bateson’s next move signaled that he was both hurt and angry. He turned to Galton to vent his frustration in a series of letters that heavily criticized Weldon’s analysis of wild crab populations [ 25 ].

A year later, the situation intensified when William Turner Thiselton-Dyer, Director of the Royal Botanic Gardens in Kew, wrote a letter to the editor of Nature in which he praised work recently presented by Weldon and Pearson stating, “I entirely agree with him in minimizing the value of ‘sports’ in evolution” [ 26 ]. This drew severe criticism from Bateson who responded the next month with his own letter to Nature announcing that he “…ventured to deal with this case because it seems to be generally supposed by those not acquainted with the facts, that the origin of the modern florists’ flowers has in general been very gradual”. Eventually, Weldon also weighed in, arguing that Bateson omitted pertinent information in his letter and that his “emphatic statements are simply evidence of want of care in consulting and quoting authorities referred to.” Bateson furiously replied, “Upon what grounds [Weldon’s] statement has been made the reader shall now learn, not perhaps without astonishment”. Weldon finally ended the quarrel saying, “Enough has been said to show that Mr. Bateson’s original evidence does in fact bear the interpretation I put upon it…Having done this, my interest in the matter ends, and I do not propose to speak further upon it” [ 27 ]. The playful argumentativeness that characterized their earlier written exchanges transformed into bitter antagonism as each became more entrenched in his own methodology and results and suspicious of the other. Eventually, Weldon wrote privately to Bateson saying, “Dear Bateson, I can do no more. First, you accuse me of attacking your personal character, and when I disclaim this, you charge me with a dishonest defense of someone else…If you insist upon regarding any opposition to your opinions concerning such matters as a personal attack upon yourself, I may regret your attitude but I can do nothing to change it” [ 28 ].

For the next few years, Bateson, Saunders, and Punnett continued to selectively breed plants and publish observations of discontinuous traits while the Weldons’ continued to gather large amounts of data from wild populations of crabs and collaborate with Pearson in London to develop statistical methods of analysis. The next plot point in the story occurred at the turn of the century when Mendel’s work was “rediscovered.” Hugo de Vries, a botanist from Austria, who was aware of Mendel’s work, attended the 1899 conference of the Royal Horticultural Society where he heard a lecture by Bateson describing the breeding experiments that he and Saunders were performing on flowering plants in Cambridge. Realizing the similarity to Mendel’s earlier pea plant experiments, De Vries published a paper in 1900 referring to the original work of Mendel in a footnote. The year 1900 marked the “rediscovery” of Mendel’s laws by De Vries, Correns, and Tschemark, and gave Bateson the independent evidence that he was seeking ( Box 3 ). He became a huge supporter of the “mendelian” theory and again, wrote to Galton, saying “In case you may miss it… Mendel’s work seems to me one of the most remarkable investigations yet made on heredity, and it is extraordinary that it should have got forgotten.” [ 29 ]. Bateson became an ardent supporter of the mendelian model of inheritance, and in 1909, Bateson translated Mendel’s work from the original German into English. Incidentally, he also named his youngest son Gregory after Gregor Mendel.

Box 3. Recent interpretations challenge the traditional account of the rediscovery of Mendel’s work

Shan argues that rediscovery is the wrong term to describe the use of Mendel’s work in the subsequent efforts of de Vries, Correns, and Tschemark. All 3 reported Mendel’s observations, but then went on to extrapolate from his work ideas that supported their own discoveries. For example, Shen argues that De Vries, not Mendel, proposed the ideas of dominance and segregation of alleles that he supported with the ratios reported by Mendel [ 15 ].

But Pearson and Weldon were skeptical of mendelian ratios believing the results were “too good to be true.” Weldon noted that in the wild, peas often varied more continuously from yellow to green. He argued that Mendel’s results may have been an artifact of the extensive inbreeding required to obtain the pure green and yellow lines prior to the hybridization experiments. His skepticism of mendelian ratios was fed by a larger concern over what he perceived as a lack of quantitative rigor in the field. In the year before Mendel’s work was rediscovered, he wrote to Pearson saying, “The contention ‘that numbers mean nothing and do not exist in Nature’ is a very serious thing, which will have to be fought. Most other people have got beyond it, but most biologists have not. Do you think it would be too hopelessly expensive to start a journal of some kind?” Weldon and Pearson (in consultation with Galton) subsequently established the journal Biometrika that produced its first issue in 1901. By 1902, the two schools of thought were cemented and colloquially named, the Mendelians (Bateson, Saunders, and Punnett) in Cambridge, and the Biometricians (Weldon and Pearson) in London. By 1904, about 15 years after the argument first began, civility was so eroded that the editor of Nature refused to publish any more letters between Weldon and Bateson on the issue of saltation versus continuous selection.

Eventually, the tension erupted in person at the 1904 meeting of the zoological section for the British Association for the Advancement of Science. The meeting was held at Cambridge, the Mendelians’ turf, and Bateson was the president of the zoological section of the society. It was no surprise that he used his presidential address to lecture on the controversy saying, “For if any one will stoop to examine Nature in those humble places… he will not wait long before he learns the truth about variation… Again and again the circumstances of their occurrence render it impossible to suppose that these striking differences are the product of continued selection, or, indeed, that they represent the results of a gradual transformation of any kind” [ 30 ]. Bateson’s words provoked an argument with Weldon on the spot. The argument grew heated and according to reports of the session, conference goers who at first were shifting uncomfortably in their seats eventually began to congregate around the embattled leaders of each side. Finally, the chair of the session, who could not subdue the animated crowd announced in exasperation “Let them fight it out!” [ 31 ]. The event was so explosive that 2 years later, when Weldon died suddenly of pneumonia, the New York Times described the scene in his obituary saying that “The debate, which was conducted before a large and somewhat agitated audience, resolved itself into a dialectical dual between the president of the section [Bateson] and Professor Weldon, and developed quite a considerable amount of heat” [ 32 ].

Over the next 2 years, the argument overtook both men. Weldon was seemingly obsessed with disproving what he perceived as a narrow interpretation of the mendelian hypothesis of inheritance (particularly dominance) in each subsequent paper in which it was proposed. His last work, “ Theory of Inheritance ,” an unpublished book with 6 manuscript chapters (historical documents held at University College London), incorporated experimental data testing mechanistic hypotheses underlying his statistical observations [ 21 ]. Shan [ 15 ] and others [ 33 ] argue that this manuscript presents a unified theory which may indeed have been the first attempt to reconcile Biometry and Mendelianism. He worked excessively long hours day after day and for many months refused a break, saying “I really want a holiday, but I cannot leave this thing unsettled” [ 4 ]. Pearson was concerned and eventually persuaded Weldon to take a vacation. The families adjourned to the English seaside for the Easter break, and it was there that Weldon caught a chest infection that developed into pneumonia. He died a few weeks later at the young age of 46. Pearson, and many others who knew Weldon, believed his premature death was in part due to frenzied overwork and stress that left him physically weakened and unable to fend off the infection. Of his friend, Pearson said: “He was by nature a poet, and these give the best to science, for they give ideas” [ 1 ].

After Weldon’s death, the raw bitterness of the Mendelian–Biometrician debate gave way to a quieter resentment that seethed between Pearson and Bateson for another decade, and Weldon’s manuscript book remained in archives. Bateson found that his influence was profound in the United States where mendelian genetics took firm root while London remained the stronghold of the Biometricians. Mendelian genetics caught on early and spread rapidly in the US, in part due to promotion by eugenicists who used genetic determinism to mobilize a racist and classist agenda that permeated US genetics and governmental policy until well after World War II. Later, after distancing genetics from eugenics, theories of mendelian inheritance continued to be the primary model taught in the US. Indeed, the consequences of this community divide can still be seen today in a comparison between UK and US genetics school curriculum.

Twenty-six-year-old Ronald Aylmer Fisher entered the fractured field in 1916, a decade after Weldon’s passing. By this time, the division between the Biometricians and the Mendelians was older than Fisher himself and had profoundly shaped the new field of genetics and an entire generation of zoologists. Fisher was in an ideal position to bridge the divide. Trained as a mathematician but working at Cambridge, the home of the mendelian experimentalists, Fisher was open to the possibility of a simple third solution that unified the observations of both sides. His paper describing this solution was first communicated by Leonard Darwin (Charles’ nephew) to the Royal Society in 1916. The paper included extensive mathematical proofs supporting the central thesis that “In general, the hypothesis of cumulative mendelian factors seems to fit the facts very accurately.”

The paper represented the potential for a formal reconciliation between the positions of the Biometricians and the Mendelians. Reginald C. Punnett and Pearson, who had been so close to the heart of the conflict between Bateson and Weldon, were asked to review. The paper was heavily mathematical and from Punnett’s perspective, too theoretical. Of the thesis, Punnett stated “I do not feel that this kind of work affects us biologists much at present. It is too much of the order of problem that deals with weightless elephants upon frictionless surfaces, where at the same time we are largely ignorant of the other properties of the said elephants and surfaces” [ 34 ]. Pearson’s review, which he started by acknowledging he was “overfussed with other work,” was similarly dismissive and asserted that the paper was of little interest to the mathematically minded and unlikely to be persuasive to biologists. He closed by stating that “Whether the paper be published or not should depend on mendelian opinion as to the correspondence of the authors hypotheses with observation, and the probability that mendelians will accept in the near future a multiplicity of independent units not exhibiting dominance or coupling” [ 34 ]. Though it was not formally rejected, the paper was considered too low impact by the journal and was eventually withdrawn [ 34 ]. It was published 2 years later, in 1918, in the Transactions of the Royal Society of Edinburgh. Today, “The correlation between relatives on the supposition of mendelian inheritance” is considered one of the most influential papers in human genetics as it provided a foundation from which the polygenic model of disease and many sophisticated molecular and quantitative approaches subsequently emerged.

However, it would still take many years of healing before the human genetics community truly integrated these ideas into praxis. As the field of medical genetics emerged, work in the US was almost exclusively focused on single-gene disorders for decades. The biometrician view of polygenicity and continuous distributions of genetic liability, which became a staple of genetics curriculum in Europe, was less frequently taught in US classrooms. Even today, many genetics students reach graduate school in the US without ever having been exposed to Fisher, Weldon, or a polygenic model of disease. In contrast, even most US middle school students have heard of Mendel’s principals of inheritance. The comparative lack of quantitative genetics in the US can be directly traced back to these early days and reminds us that even our local science culture can be shaped by the personality and priorities of distant scientists with a bully pulpit.

Weldon and Bateson were, as most scientists are, fanatical truth-seekers who shared the radical belief that nature’s truths are discoverable. Their legacy demonstrates that despite the nobility and beauty of this shared journey, we move slowly, hampered by the ignoble baggage that complicates our relationships. The lesson from this story is simple, but not easy. Science without humility and community slows our collective understanding. The history of science in the Western academy is fraught with stories like this one. In Western cultures, we often attribute discovery to individuals instead of communities, effectively making scientific discovery appear highly personal and individualistic. Furthermore, our competitive instincts to win arguments are seeded and nurtured by academic institutions that reward “being right” and punish mistakes without acknowledging that we can rarely have the former without the latter. Further, in today’s climate of rapid-fire response on social media, the community norms for engaging in scientific debate can easily erode even further. None of us is immune to the deafening arrogance of competition or the blinding lure of peer admiration, and this individualistic culture leaves science itself vulnerable as fractures develop in the community. These fractures then slow collaboration and provide a breeding ground for disinformation campaigns, the scale of which continues to grow.

My own experience is obviously limited, and yet, there may be value in sharing that experience. After 20 years in academic science, and a range of team–science interactions, it is my observation that when a scientific community is guided by a philosophy of “open-hearted curiosity,” healthy collaborations are born and important discoveries follow. What does this mean? Unfortunately, open-heartedness (and even open-mindedness) can sometimes be perceived as a weakness, somehow lacking in scientific rigor. But rigor should not be confused for ruthlessness, and open-hearted curiosity does not imply a lack of skepticism. In fact, skepticism is inherent to curiosity. Richard Feynman once said, “Science is the belief in the ignorance of experts,” and went on to explain that scientists must be trained to “both to accept and to reject the past with a kind of balance that takes considerable skill.” I argue that curiosity is the fundamental driver of this balance. The curious person does not accept assertions without evidence, they need to see, poke, and prod the data for themselves.

Curiosity alone cannot sustain healthy collaboration, but open-heartedness can protect it from toxicity. The open-hearted scientist is willing to share what they know and willing to be open and honest about what they do not know or do not yet understand. For academicians, this strikes at the heart of a vulnerability that most achievement-oriented education systems have implicitly encouraged us to hide. How can we be “experts” in our field and admit that we are ignorant? And yet, if we agree with Feynman’s astute observation of science, we are compelled to so. From an open-hearted perspective, we can shed the judgement of our ignorance, and instead appreciate that it is the raw material of future discovery. The wonderful thing about this approach is that it further compels us to question everything from our own motivations to our understanding of the data in front of us. Open-hearted curiosity provides a safe space for us to deepen our questioning. The open-hearted person further recognizes that good ideas can come from anywhere, listens without prejudice, and values the humanity of those around them. Indeed, approaching scientific problems with open-hearted curiosity is a rigorous practice that requires a great dose of humility and relentless perseverance.

Could Bateson and Weldon have benefited from open-hearted curiosity? Theirs was an era of robust debate and independent science. Their debates took on a sporting quality, as exemplified during the 1904 conference. But this model of scientific discourse may have been doomed from the beginning. After all, in the end, debate for sport is unambiguously about winning. Each side digs their heels in and aims to persuade as many people as possible. There is very little room for ambiguity and admitting any vulnerability or questioning one’s own view is a game-ending move in a sporting debate. But in a culture that explicitly values the search for truth, and not the ego of the scientist, scientific debate has an entirely different quality and outcome. It is no longer a sport with a single dominating champion. It becomes a scaffolded work of art, an improvisational jazz piece composed through individual creativity and communal effort. In this style of debate, parties lock intellects and together come to a deeper understanding of the world around them. In retrospect, I wonder how far Weldon and Bateson, together, could have pushed the field if they had matured in a climate of open-hearted curiosity.

When we engage each other with ego, we risk contaminating the worthiness of our shared pursuit with our own self-interests. On the other hand, if we can adopt a cultural expectation of open-hearted curiosity and learn to recognize and soothe our own insecurities, if we can allow ourselves to be vulnerable about what we do not know, if we can trust each other to share honestly and without judgement or pretense, we can create a principled scientific community deserving of discovery. We have the awesome responsibility of understanding and communicating the stuff that makes us human. These are bigger questions than we can fathom alone, and we are never so worthy to learn the secrets of the universe as when we humble ourselves to their complexity.

Acknowledgments

I wish to thank Tad Davis, Nancy Cox, Naomi Wray, Peter Visscher, Sara Van Driest, Anthony (Tony) Capra, and Laurel Waycott for their encouragement and feedback on early drafts of this work.

Funding Statement

The authors received no specific funding for this work.

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Godfrey Hardy and Reginald Punnett

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Godfrey Hardy and Reginald Punnett both used math in their analysis of biological events.

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