albino frosch experiment

"The Developmental Capacity of Nuclei Taken from Intestinal Epithelium Cells of Feeding Tadpoles" (1962), by John B. Gurdon

In 1962 researcher John Bertrand Gurdon at the University of Oxford in Oxford, England conducted a series of experiments on the developmental capacity of nuclei taken from intestinal epithelium cells of feeding tadpoles. In the experiments, Gurdon conducted nuclear transplantation, or cloning, of differentiated cells, or cells that have already specialized to become one cell type or another, in tadpoles. Gurdon's experiment showed that differentiated adult cells could be induced to an undifferentiated state, where they could once again become multiple cell types. Gurdon's experiment disproved the theory that differentiated cells could not be undifferentiated or dedifferentiated into a new type of differentiated cell. Gurdon's experiment demonstrated nuclear transplantation, also called cloning, using differentiated cells.

In 1960, Gurdon obtained his doctorate in zoology at the University of Oxford after researching new techniques of nuclear transplantation in Xenopus laevis , a species of frog. Gurdon conducted his experiment with tadpoles in the embryology laboratory at the Department of Zoology at the University of Oxford.

Gurdon's experiments built on research conducted by Robert Briggs and Thomas King who performed the first nuclear transfer in living organisms in 1952. Nuclear transfer is the process of transplanting the nucleus of one cell into an unfertilized enucleated egg cell, a cell whose nucleus was removed. Prior to Gurdon's experiments, Briggs and King had argued that nuclear transfer was impossible if the cells used in the transplantation had already developed beyond a certain point. The theory, supported by Briggs and King's experiment, was that once a cell differentiates, the cell could no longer differentiate again. Gurdon questioned whether cells lose certain genes after they specialize that consequently prevent them from transforming into new cell types.

Gurdon's series of experiments aimed at determining whether cells, as they develop and specialize, lose the ability to produce different cell types. In his experiments, Gurdon transplanted nuclei from tadpole cells of Xenopus , and other frog species, into unfertilized Xenopus eggs and observed how the modified eggs proceeded to develop. Gurdon stopped the development of some the modified eggs, or fixated them, and allowed others to develop as far as they were able. He compared them and noted trends in development based on the conditions of the fixed eggs. Gurdon also tested whether using nuclei of eggs produced through nuclear transfer to produce successive generations of eggs led to eggs that developed to a further stage.

Gurdon collected donor cells from the mid-intestine of Xenopus tadpoles, a developmental stage of frogs preceding adulthood. Gurdon selected mid-intestine cells because they were larger and easier to see due to a specific striation pattern that differed from other cell types present in the intestine. Gurdon noted that the quality of Xenopus eggs laid in the laboratory were of varying quality due to the artificial conditions of the laboratory. To account for that variability, Gurdon also used cells from the same developmental stage that Briggs and King had used to serve as the control group.

In the first experiment, Gurdon performed nuclear transfer using a donor mid-intestinal nucleus from a Xenopus tadpole and an unfertilized egg of the same frog species. To accomplish nuclear transfer, Gurdon first softened the outer layer of the unfertilized egg with UV radiation. That step degraded the nucleus of the egg and also weakened the cell membrane, enabling Gurdon to inject a nucleus from a different cell into the unfertilized egg cell using a pipette, or a small needle-like measurer. After transplanting nuclei into many egg cells, Gurdon stopped the development of some of the modified eggs, a process called fixation. By fixating the eggs, Gurdon was able to study the modified egg at an exact point in time. Gurdon allowed the remaining eggs to develop normally and then compared the fixed and unfixed eggs. Gurdon sliced the fixed eggs into sections and viewed the sections under a microscope. He found that many of the transplanted nuclei had abnormalities. Gurdon concluded that certain abnormalities in the transplanted nuclei led to specific abnormalities in development.

Gurdon noted several trends when he compared the fixed eggs to the unfixed eggs. He found that many of the eggs did not experience cleavage, the process of egg division, after transplantation. Cleavage enables a fertilized egg to divide and produce the many cells that will make up the organism. Gurdon concluded that the lack of cleavage was the result of a technical fault in which the transplanted nuclei were not effectively exposed to the cytoplasm, or cellular material within the cell, of the egg. The cytoplasm of the egg is crucial in the process of cleavage because it signals the nuclei to induce cleavage. Gurdon also noticed that some eggs did not have a nucleus and he concluded that the absence of the nucleus was most likely due to the accidental removal of the nuclei after transplantation due to the nucleus sticking to the pipette. Those technical errors caused eggs not to develop beyond a certain stage, halting their development.

In the second experiment, Gurdon transplanted the intestinal nucleus from a different species of frog, called Hymenochirus curtipes into the unfertilized Xenopus eggs to see whether using different species affected the rates of abnormal cleavage. By using nuclei from the frogs of another species, Gurdon could observe the genetic differences between species led to abnormal cleavage. Gurdon transplanted the nuclei of H. curtipes , and the nuclei of Xenopus into unfertilized Xenopus eggs. Xenopus eggs that received H. curtipes nuclei experienced early arrest, while many of the Xenopus eggs that received Xenopus nuclei developed normally. Gurdon noted that the percentage of transfers that experienced halted development was the same in each nuclear transfer. Once the eggs reached the blastula stage, or the early embryonic stage during which a hollow sphere of cells form, the eggs that received the genetically different donor nuclei from the different frog species stopped developing. The eggs receiving the genetically identical donor nuclei from the same species continued to develop. He concluded that genetically different donor nuclei did not have higher rates of abnormal cleavage than genetically identical donor nuclei, which meant that the genetic difference did not cause the abnormal cleavage.

Gurdon performed the third experiment to determine whether the quality of eggs increased or decreased with each successive generation. To do so, he enucleated eggs as he had done previously and inserted donor nuclei into the eggs. Gurdon then allowed the modified eggs to develop. He referred to those as first-transfer eggs. He then removed the nuclei of the first-transfer eggs and performed nuclear transfer once again, a step he called serial-transfer. That gave rise to the first serial-transfer generation of eggs. Gurdon found that in all cases, the serial-transfer eggs developed to a further stage than the first transfer eggs.

Gurdon posed two possible explanations for the results of the third experiment. The first was that the nuclei's ability to develop increased after nuclear transfer was performed, causing the serial-transfer eggs to develop further than the first-transfer eggs. The second possibility was that the abnormality of the first-transfer embryo was due to poor egg quality or to genetic causes.

To determine which explanation was correct, Gurdon created multiple serial-transfer generations of eggs. The later generations did not contain more abnormal cleavage events than did the earlier generations. From those results, Gurdon concluded that developmental capacity does not increase as a result of multiple, serial-transplants.

Based on the results of the three experiments, Gurdon concluded that the cell types produced after transplantation indicated the genetic information contained within the transplanted nucleus. Likewise, he argued that the transplanted nucleus must contain the information supporting the development of a normal tadpole.

Gurdon hypothesized that some cells may become differentiated under the influence of neighboring cells due to cell to cell communication, which would explain why some cells in a specific tissue contain the nuclei that have the genetic information to form a normal tadpole. Further, Gurdon argues that the cytoplasmic environment of a cell initiates differentiation and that the nucleus provides the information to code for a particular cell type.

The experiment showed that cloning could be performed with the nucleus of more types of cells than previously thought. In 1997, the technology used by Gurdon in his 1962 article was later used in the cloning of a sheep named Dolly, demonstrating the wide range of possibilities made possible by nuclear transfer.

• Briggs, Robert, and Thomas J. King. "Transplantation of Living Nuclei from Blastula Cells into Enucleated Frogs Eggs." Proceedings of the National Academy of Sciences of the United States of America 38 (1952): 455–63. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1063586/ (Accessed August 11, 2016).
• Campbell, Nick. "Turning Back Time." Nature.com. July 1, 2004. http://www.nature.com/milestones/development/milestones/full/milestone5.html (Accessed October 23, 2015).
• Elsdale, Tom R., John B. Gurdon, and Michael Fischberg. "A Description of the Technique for Nuclear Transplantation in Xenopus Laevis." Journal of Embryology and Experimental Morphology 8 (1960) 437–44. http://dev.biologists.org/content/develop/8/4/437.full.pdf (Accessed August 10, 2016).
• Gurdon, John B. "Factors Responsible for the Abnormal Development of Embryos Obtained by Nuclear Transplantation in Xenopus laevis." Development 8 (1960): 327–40. http://dev.biologists.org/content/develop/8/3/327.full.pdf (Accessed August 11, 2016).
• Gurdon, John B. "The Developmental Capacity of Nuclei Taken from Intestinal Epithelium Cells of Feeding Tadpoles." Development 10 (1962):622–40. http://dev.biologists.org/content/develop/10/4/622.full.pd (Accessed August 10, 2016).
• Gurdon, John B. "Transplanted Nuclei and Cell Differentiation." Scientific American 219 (1968): 24–35. http://www.scientificamerican.com/article/transplanted-nuclei-and-cell-differentiation-gurdon/ (Accessed February 8, 2017).
• Gurdon, John B. "The Egg and the Nucleus: A Battle for Supremacy." Lecture at the 2012 Nobel Prize in Physiology or Medicine, Stockholm, Sweden, December 7, 2012. https://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/gurdon-lecture.pdf (Accessed August 10, 2016).

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October 9, 2012

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Transplanted Nuclei and Cell Differentiation, by Sir John B. Gurdon

The nucleus of a cell from a frog's intestine is transplanted into a frog's egg and gives rise to a normal frog. Such experiments aid the study of how genes are controlled during embryonic development

By John B. Gurdon

Editor’s note (10/9/2012): We are making the text of this article freely available for 30 days because the author, Sir John B. Gurdon, is one of the winners of the 2012 Nobel Prize in Physiology or Medicine . The full article with images, which was published in the December 1968 issue, is available for institutional users only at this time ( pdf ).

The means by which cells first come to differ from one another during animal development has interested humans for nearly 2,000 years, and it still constitutes one of the major unsolved problems of biology. Much of the experimental work designed to investigate the problem has been done with amphibians such as frogs and salamanders because their eggs and embryos are comparatively large and are remarkably resistant to microsurgery. As with most animal eggs, the early events of amphibian development are largely independent of the environment, and the processes leading to cell differentiation must involve a redistribution and interaction of constituents already present in the fertilized egg.

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Several different kinds of experiment have revealed the dependence of cell differentiation on the activity of the genes in the cell's nucleus. This is clearly shown by the nonsurvival of hybrid embryos produced by fertilizing the egg of one species (after removal of the egg's nucleus) with the sperm of another species. Such hybrids typically die before they reach the gastrula stage, the point in embryonic development at which major cell differences first become obvious. Yet the hybrids differ from nonhybrid embryos only by the substitution of some of the nuclear genes. If gene activity were not required for gastrulation and further development, the hybrids should survive as well as nonhybrids. The importance of the egg's non-nuclear material—the cytoplasm—in early development is apparent in the consistent relation that is seen to exist between certain regions in the cytoplasm of a fertilized egg and certain kinds or directions of cell differentiation. It is also evident in the effect of egg cytoplasm on the behavior of chromosomes [see "How Cells Specialize," by Michail Fischberg and Antonie \V. Blackler; SCIENTIFIC AMERICAN, September, 1961]. Such facts have justified the belief that the early events in cell differentiation depend on an interaction between the nucleus and the cytoplasm.

Nuclear transplantation is a technique that has enormously facilitated the analysis of these interactions between nucleus and cytoplasm. It allows the nucleus from one of several different cell types to be combined with egg cytoplasm in such a way that normal embryonic development can take place. Until this technique was developed the only kind of nucleus that could be made to penetrate an egg was the nucleus of a sperm cell, and this was obviously of limited use for an analysis of those interactions between nucleus and cytoplasm that lead to the majority of cell differences in an individual.

The technique was first applied to the question primarily responsible for its development. The question is whether or not the progressive specialization of cells during development is accompanied by the loss of genes no longer required in each cell type. For example, does an intestine-cell nucleus retain the genes needed for the synthesis of hemoglobin, the protein characteristic of red blood cells, and a nerve-cell nucleus the genes needed for making myosin, a protein characteristic of muscle cells? If unwanted genes are lost, the possibility exists that it is the progressive loss of different genes that itself determines the specialization of cells, as August Weismann originally proposed in 1892. The clearest alternative is that all genes are retained in all cells and that the genes are inactive in those cells in which they are not required. Before describing the nuclear-transplant experiments that distinguish between these two possibilities, we must outline the methods used to transplant living cell nuclei into eggs.

The aim of a nuclear-transplant experiment is to insert the nucleus of a specialized cell into an unfertilized egg whose nucleus has been removed. Ingenious attempts in this direction were made many years ago by constricting an egg just after fertilization and then letting one of the early-division nuclei that appeared in the nucleated half of the egg enter the non-nucleated half. This method, however, is applicable only to the nuclei of early embryos whose cells are not normally regarded as being specialized. The first real success in transplanting living cell nuclei into animal eggs was achieved in 1952 by Robert W. Briggs and Thomas J. King, both of whom were working at the Institute for Cancer Research in Philadelphia. Their method, which has been generally adopted in subsequent work, involves three steps. Owing to the fortunate circumstance that the unfertilized egg of an amphibian has its nucleus (in the form of chromosomes) located just under the surface of the egg at a point visible through the microscope, it is not difficult to obtain an egg with no nucleus. This can be done by removing the region of the egg that contains chromosomes with a needle or by killing the nuclear material with ultraviolet radiation. The second step is to dissociate a tissue into separate cells, each of which can be used to provide a donor nucleus for transplantation. The cells separate from one another in a medium lacking calcium and magnesium ions, which are removed from the embryo more quickly by adding to the medium a chelating substance such as Versene.

The third and most difficult stage in the procedure involves the insertion of the donor-cell nucleus into the enucleated egg. Briggs and King found that this can be done by sucking an isolated cell into a micropipette that is small enough to break the cell wall but large enough to leave the nucleus still surrounded by cytoplasm. This compromise is required because the nucleus in an unbroken cell does not make the necessary response to egg cytoplasm, and conversely a bare nucleus without surrounding cytoplasm is readily damaged by exposure to any artificial medium. The broken cell with its cytoplasm-protected nucleus is injected into the recipient egg. The amount of donor-cell cytoplasm injected is very small and does not have any effect.

A useful extension of the basic nuc1ear-transplant technique is called serial nuclear transplantation. It involves the same procedure as the one just described except that instead of the donor nuclei being taken from the cells of an embryo or larva reared from a fertilized egg,            they are taken from a young embryo that is itself the result of a nuclear­ transplant experiment. The effect is the same as in the vegetative propagation of plants, namely the production of a clone: a population consisting of many individuals all having an identical set of genes in their nuclei.

One other feature of nuclear-transplant experiments is of the greatest importance for their interpretation. It is the use of a nuclear marker whereby the division products of a transplanted nucleus can be distinguished from those of the host egg nucleus. A nuclear marker is virtually indispensable where attention is to be paid to the development of a very small percentage of eggs that have received transplanted nuclei, since one cannot otherwise be sure that an occasional error in enucleation by hand or by ultraviolet irradiation has not occurred. Only by the presence of a marker in the nuclei of a transplant embryo does one have proof of its origin.

A nuclear marker must be replicated and therefore be genetic. One of the most useful for nuclear transplantation is found in a mutant line of the South African clawed frog Xenopus laevis , discovered at the University of Oxford by Michail Fischberg. The nuclei of most normal frog cells contain two of the bodies called nucleoli; the nuclei of cells carrying the mutation never have more than one. This mutation is almost ideal as a nuclear marker because a sample of cells taken from any tissue at any develop­ mental stage beyond the blastula (the hollow sphere from which the gastrula arises) can be readily classified as being mutant or not.

We can now return to the question of whether or not genes are lost in the course of normal cell differentiation. Nuclear-transfer experiments are performed to answer this question on the assumption that if the combination of egg cytoplasm with a transplanted nucleus can develop into a normal embryo possessing all cell types, then the transplanted nucleus cannot have lost the genes essential for pathways of cell differentiation other than its own. For example, if a normal embryo containing a specialized cell type such as blood cells can be obtained by transplanting an intestine-cell nucleus into an enucleated egg, then the genes responsible for the synthesis of hemoglobin cannot have been lost from the intestine-cell nucleus in the course of cell differentiation. The only assumption here is that a gene, once lost, cannot be regained in the course of a few cell generations. It happens that the best evidence for the retention of genes in fully differentiated cells comes from two series of experiments carried out at Oxford on eggs of the frog Xenopus .

The fully differentiated cells used for these experiments were taken from the epithelial layer of the intestine of mutant tadpoles that had begun to feed. Intestine epithelium cells have a "brush border," a structure that is present only in cells specialized for absorption and that is assumed to have arisen as a result of the activity of certain intestine-cell genes. Not all the cells of the intestine are epithelial, but when the epithelial cells are dissociated, they can be distinguished from the other cell types by their large content of yolk, by the ease with which they dissociate in a medium that contains Versene and sometimes by their retention of the brush border.

The first experiments with intestine­cell nuclei were designed to show that at least some of these nuclei possess all the genes necessary for the differentiation of all cell types, and therefore that some of the transplant embryos derived from intestine nuclei could be reared into normal adult frogs. Both male and female adult frogs, fertile and normal in every respect, have in fact been obtained from transplanted intestine nuclei. Although only about 1.5 percent of the eggs with transplanted intestine nuclei developed into adult frogs, all of these frogs carried the mutant nuclear marker in their cells; their existence therefore proves that at least some intestine cells possess as            many different            kinds of nuclear genes as are present in a fertilized egg.

Subsequent experiments with intestine nuclei were designed to show that many of these nuclei have retained genes required for the differentiation of at least some quite different cell types. In these experiments the criterion for gene retention was the differentiation of functional muscle and nerve cells by nuclei whose mitotic ancestors had already promoted the differentiation of intestine cells. Functional muscle and nerve cells are present            in any nuclear-transplant embryo that shows the small twitching movements, or muscular responses, characteristic of            developing tadpoles just before they swim. Out of several hundred intestine nuclear transfers, about 2.5 percent of the injected eggs developed as far as the muscular-response stage or further. The reason why the remainder did not reach this stage is not necessarily because that proportion of intestine nuclei lack the necessary genes. In some cases it is known to be the inability of certain recipient eggs to withstand injection; in others it is the incomplete replication of some of the transplanted nuclei or their daughter nuclei during cleavage. In either case            a nuclear-transplant embryo should contain some cells with normal nuclei as well as some abnormal cells responsible for the early death of the embryo.

Serial nuclear transplantation offered a means of overcoming both difficulties. A sample of nuclear-transplant embryos whose development was so abnormal they would have died before reaching the muscular-response stage provided nuclei for serial-transplant clones. In 70 percent of the serial-transplant clones some of the embryos developed as far as the muscular-response stage or beyond it. By adding the proportion of nuclei shown by first transplants to be able to support muscular-response differentiation to the proportion shown by serial transplantation to possess this capacity, we can conclude that at least 20 percent of the intestine epithelium cells must have retained the genes necessary for muscle-cell and nerve-cell differentiation.

There is no reason to believe that muscle-cell or nerve-cell genes have been lost or permanently inactivated in the remaining 80 percent of transplanted intestine nuclei. There are many reasons why it might not have been possible to demonstrate their presence. For example, about 50 percent of all the eggs that received intestine nuclei failed to divide even once. When a sample of these eggs was sectioned, they were found to contain either no nucleus at all or else a nucleus that was still inside an intact intestine cell. In the first instance the nucleus presumably stuck to the injection pipette and was never deposited in the egg; in the second, the donor cell was never broken so as to liberate its nucleus, a technical error that is easy to make with very small cells. In both cases the developmental capacity of the intestine nuclei was not tested, and the recipient eggs that failed to divide should not be counted in the results.

It is clear from these experiments that the loss or permanent inactivation of genes does not necessarily accompany the normal differentiation of animal cells. This conclusion is not inconsistent with a recent finding: the "amplification" of the genes responsible for synthesizing the ribonucleic acid (RNA) of the sub­ cellular particles called ribosomes. This phenomenon was demonstrated in amphibian oocytes, the cells that give rise to mature eggs. The nuclear-transfer experiments just described do not exclude such amplification, which simply alters the number of copies of one kind of gene in a nucleus. Instead they show that specialized cells always have at least one copy of every different gene.

The inability of some transplanted nuclei to support normal development has attracted considerable interest be­ cause it is always found that the proportion of nuclei showing a restricted developmental capacity increases as the cells from which they are taken become differentiated. Furthermore, serial nuclear-transplant experiments conducted by Briggs and King (and subsequently by others) have shown that all the embryos in a clone derived from one original nuclear transplant often suffer from the same abnormality, whereas the embryos in a clone derived from another original transplant may suffer from a different abnormality. Some of the abnormalities of nuclear-transplant embryos can therefore be attributed to nuclear changes that can be inherited.

The discovery that these changes arise as a result of nuclear transplantation, and not in the course of normal cell differentiation, was an important one. This was first established by Marie A. DiBerardino of the Institute for Cancer Research, who made a detailed analysis of the number and shape of chromosomes in nuclear-transplant embryos. Abnormal embryos were usually found to suffer from chromosome abnormalities that were not present in the donor embryos, a finding that at once explains why the factors causing many of the developmental abnormalities of nuclear-transplant embryos are inherited. The fact that chromosome abnormalities arise after nuclear transplantation does not necessarily mean that they are of no interest; there could be a connection between the kind of chromosome abnormality encountered and the cell type of the donor nucleus concerned. In spite of an intensive search, however, no such relationship has yet been found.

The origin of these chromosome abnormalities is probably to be understood as an incompatibility between the very slow rate of division of differentiating cells—only one division every two days or more—and the rapid rate of division in an egg, which starts to divide (and causes any injected nucleus to try to divide) about an hour after injection. Unless an injected nucleus can complete the replication of its chromosomes within this brief period, they will be torn apart and broken at division. This concept is supported by the observation, made at Oxford in collaboration with my colleagues C. F. Graham and K. Arms, that many transplanted nuclei continue to synthesize the genetic material DNA right up to the time of the first nuclear division, whereas sperm and egg nuclei always complete this synthesis well before division. Presumably molecules associated with the DNA of specialized cells prevent the chromosomes of such cells from undergoing replication as rap­ idly as those of sperm nuclei, thereby leading to the chromosome abnormalities commonly observed in nuclear-trans­ plant embryos.

Having concluded that the specialization of cells involves the differential activity of genes present in all cells, rather than the selective elimination of unwanted genes, we can now consider how genes are activated or repressed during early embryonic development. Nuclear transplantation has been used to demonstrate that the signals to which genes or chromosomes respond are normal constituents of cell cytoplasm. This information has come from experiments in which the nucleus of a cell carrying out one kind of activity is combined with the enucleated cytoplasm of a cell whose nucleus would normally be active in quite another way. One of two results is to be expected: either the transplanted nucleus should continue its previous activity or it should change function so as to conform to that of the host cell to whose cytoplasm it has been exposed. For the purposes of these experiments changes in nuclear activity have to be recognized by the appearance of direct gene products and not by the much less direct criterion of the normality of nuclear-transplant embryo development. Many of these experiments have been carried out in collaboration with Donald D. Brown of the Carnegie Institution of Washing­ ton or with another of my Oxford colleagues, H. R. Woodland.

The first experiments were designed to find out if the different functions performed by any one gene—the synthesis of DNA, the synthesis of RNA and chromosome condensation in preparation for cell division—are determined by cytoplasmic constituents. Three kinds of host cell were used: unfertilized but activated eggs whose nucleus would normally synthesize DNA but no RNA; growing oocytes in which the nucleus synthesized RNA but not DNA, and oocytes maturing into eggs, in which situation the nucleus consists of condensed chromosomes arranged in the "spindle" of cell division, and synthesizes neither RNA nor DNA. Two kinds of test nuclei were used: nuclei from adult brain tissue, which synthesize RNA but almost never synthesize DNA or divide, and nuclei from embryonic tissue at the mid­ blastula stage of development; mid-blastula nuclei do not synthesize RNA but synthesize DNA and divide about every 20 minutes. For technical reasons it was desirable to inject each host cell with many nuclei, even though this can prevent the subsequent division of the injected cell. The results were clear: In all respects tested the transplanted nuclei changed their function within one or two hours so as to conform to the function characteristic of the normal host-cell nucleus. Mid-blastula nuclei injected into growing oocytes stopped synthesizing DNA and dividing and entered a continuous phase of RNA synthesis that lasted for as long as the injected oocytes survived in culture (about three days). Adult brain nuclei injected into eggs stopped RNA synthesis and began DNA synthesis. When the same nuclei were injected into maturing oocytes, they synthesized neither RNA nor DNA but were rapidly converted into groups of chromosomes on spindles.

The next set of experiments was designed to find out if cytoplasmic components can repress or activate genes, that is, if they can select which genes in a nucleus will be active at any one time. Advantage was taken of the natural dissociation that exists in the time of synthesis of different classes of RNA during the early embryonic development of Xenopus . The work of several investigators has established the following sequence of events in Xenopus embryos. For the first 10 divisions after fertilization no nuclear RNA synthesis can be detected. Just after this—at the mid-late blastula stage—the cells synthesize large RNA molecules, which are believed not to include ribosomal RNA but which are likely to include "messenger" RNA. Toward the end of the blastula stage "transfer" RNA synthesis is first detected; this is followed a few hours later, during the formation of the gastrula, by the synthesis of ribosomal RNA.

The extent to which these events are under cytoplasmic control has been investigated by transplanting into enucleated eggs single nuclei from embryonic tissue at the neurula stage of development, the one that follows the gastrula stage. As the nuclear-transplant embryos develop, RNA precursor substances that have been labeled with radioactive   atoms (for example uridine triphosphate labeled with tritium, the radioactive form of hydrogen) are used to determine the classes of RNA being synthesized at each stage. Autoradiography has shown that a neurula nucleus, which synthesizes each main kind of RNA, stops all detectable RNA syntheis, that is, it no longer incorporates labeled RNA precursors, within an hour of transplantation into egg cytoplasm. Furthermore, chromatography and other kinds of analysis show that, when the transplant embryos are reared through the blastula and gastrula stages, they synthesize heterogeneous RNA, transfer RNA and ribosomal RNA in turn and in the same sequence as do embryos reared from fertilized eggs.

Taken together, these experiments have shown that changes in the type of gene product (for example the synthesis of RNA or DNA), as well as changes in the selection of genes that are active (for example the synthesis of different types of RNA), can be experimentally induced. Since a high proportion of transplanted neurula nuclei support entirely normal development, the results show that egg cytoplasm must contain constituents responsible for independently controlling the activity of different classes of genes in normal living            nuclei.

We can now consider what is perhaps the most interesting question of all: What is the mechanism by which cytoplasmic components bring about changes in gene activity? Of the various changes in chromosome and gene activity that can be experimentally induced in transplanted nuclei, special attention has been devoted to the induction of DNA synthesis by egg cytoplasm. It is easier to analyze than other changes, and it seems likely to exemplify certain general principles of cytoplasmic regulation in early embryonic development.

The origin of the cytoplasmic condition that induces            DNA synthesis has been investigated by injecting adult brain nuclei, together with a radioactive labeling substance, into growing and maturing oocytes. The inducing factor appears just after an increase in the level of pituitary hormone has caused an oocyte to mature into an egg, an event that is accompanied by intensive RNA and            protein            synthesis.

Concerning the identity of the inducing factor, the first candidate to be considered was simply the presence of an adequate supply of DNA precursor substances. Woodland, however, has injected growing oocytes with 10 times the amount of all four common DNA precursors believed to be present in the mature egg. One of the precursors, thymidine triphosphate, had been labeled with tritium. In spite of the availability of these precursors, the brain nuclei did not incorporate the labeled thymidine into DNA. Although this experiment requires further analysis before DNA precursors can be excluded as inducers of DNA synthesis, it encourages a search in other directions.

The next candidate to be considered was DNA polymerase, an enzyme that promotes the incorporation of precursor substances into new DNA in a way that is specified by the composition of the preexisting "template" DNA. DNA polymerase activity in living cells has been tested by introducing purified DNA and tritium-labeled thymidine into eggs. In collaboration with Max Birnstiel of the University of Edinburgh we have established that the injected DNA serves as a template for synthesis of the same kind of DNA. When DNA and labeled thymidine are introduced into oocytes, no DNA replication can be detected. This means that the cytoplasmic factor in­ ducing DNA synthesis in eggs includes DNA polymerase or something that ac­ tivates this enzyme. It is doubtful, how­ ever, that this is the only constituent of the inducer. If it were, the injection of egg cytoplasm (which contains DNA polymerase) into oocytes might be expected to induce DNA synthesis, a result that is not in fact obtained. This experiment, in which purified DNA is replicated in the cytoplasm of unfertilized eggs, also serves to demonstrate that constituents of injected brain nuclei other than their DNA are not required in order to initiate the particular reaction being discussed here.

The last aspect of this reaction on which some information is available concerns the mechanism by which the inducing factors in the cytoplasm interact with the DNA in the nucleus. It was noticed several years ago by Stephen Subtelny, now at Rice University (and subsequently by others), that transplanted nuclei increase in volume soon after they have been injected into eggs. A pronounced swelling is also observed in nuclei injected into oocytes; the swelling is therefore not directly related to a particular type of nuclear response. During this nuclear enlargement chromatin (which contains the genetic material in the nucleus) becomes dispersed and, as Arms has demonstrated, cytoplasmic protein also enters the swelling nuclei. While            working at Oxford, Robert W. Merriam of the State University of New York at Stony Brook found a close temporal relation between the passage of cytoplasmic protein into enlarging nuclei and the initiation of DNA synthesis. The interpretation of these events currently favored by those of us involved in the experiments is that the nuclear swelling and chromatin dispersion facilitate the association of cytoplasmic regulatory molecules with chromosomal genes, thereby leading to a change in gene activity of a kind determined by the nature of the molecules that enter the nucleus.

The experiments described here have established two general conclusions. First, nuclear genes are not necessarily lost or permanently inactivated in the course of cell differentiation. Second, major changes in chromosome function as well as in different kinds of gene activity can be experimentally induced by normal constituents of living cell cytoplasm. The same type of experiment is now proving useful in attempts to determine the identity of the cytoplasmic components and their mode of action.

We have had to restrict our attention to what can be described as sequential changes in gene activity, that is, differences between one developmental stage and the next. These may be compared with regional variations in nuclear activity, that is, differences between one part of an embryo and another at the same developmental stage. The latter are hard to study biochemically because of the difficulty in obtaining enough material. There is no obvious reason, however, why the processes leading to the two types of differentiation should be fundamentally different.

Experiments analogous to those described here have been conducted with bacteria infected with viruses, with nuclear transplantation in protozoans and with fusion in mammalian cells. Each kind of material is well suited for certain problems; nuclear transplantation utilizing amphibian eggs and cell nuclei is especially suited to the analysis of processes that lead to the first major differences between cells. Only after these differences have been            established by constituents of egg cytoplasm are cells able to respond differentially to the important agents that guide development, such as inducer substances and hormones. Finally, the technique of nuclear transplantation may be used to introduce cell components other than the nucleus into the cytoplasm of different living cells; this is likely to be of great value for the more detailed analysis of early development and cell differentiation.

Xenopus laevis (Südafrikanischer Krallenfrosch)

• First Online: 26 March 2019

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Zusammenfassung

Der Südafrikanische Krallenfrosch Xenopus laevis ist einer der Klassiker in der Reihe tierischer Modellorganismen. Die große Anzahl an sich außerhalb des Muttertiers entwickelnden Nachkommen gepaart mit der Größe der Eizellen erlaubte zahlreiche fundamentale Entwicklungsbiologische Fragen aufzuklären. Darüber hinaus wurden mit diesem Modellorganismus auch Nobelpreise in der klassischen Physiologie (Funktion der Aquaporine) und der Stammzellforschung gewonnen.

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• Published: 03 August 2006

Housing, husbandry and handling of rodents for behavioral experiments

• Robert M J Deacon 1  

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Most animals used in research are rodents, mainly mice because of their predominance in genetics and molecular biology. This article attempts to provide an introduction to mice and rats: health considerations (of the experimenter); choice of species, age, strain and sex; housing and environmental enrichment; and animal identification, handling and dosing. These considerations apply to animal work in general; the rest of the article focuses on the preliminary aspects of behavioral testing, including a protocol for an open field test. This procedure is traditionally associated with activity measurements, and although automated versions are readily available these days, the latter are expensive and may be unavailable in many non-behavioral departments. Moreover, particularly when testing novel genetically modified animals or pharmacological agents, there is no substitute for direct visual observation to detect abnormal signs in the animals: for example, ptosis, piloerection, tremor, ataxia or exophthalmos. The open field test can be adapted in several ways: to assess general behavior and activity (similar to a primary screen in the pharmaceutical industry) or to measure memory (habituation) or anxiety.

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This work was supported by grant GR065438MA from the Wellcome Trust to the Oxford group.

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Deacon, R. Housing, husbandry and handling of rodents for behavioral experiments. Nat Protoc 1 , 936–946 (2006). https://doi.org/10.1038/nprot.2006.120

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What is the modern experiment in which a frog was heated at the slowest rate?

I did a bit of research on the boiling frog phenomenon. It turned out that:

• In the 19th century, there have been done three experiments in which a frog in water was heated very slowly. It didn't jump out and then it died.
• Modern experiments did also heat frogs, and they did jump out.
• Actually, a frog dies in water of $40^{\circ}$ C. Therefore, to properly conduct the experiment the water should be heated from a normal temperature to 40 degrees.

In order to prove that the 19th century experiments were wrong, there should be a modern experiment where the frog is heated just as slowly as in the 19th century. According to Edward Wheeler Scripture (see Wikipedia ), he performed the experiment with a rate of 0.002 degrees per second.

Are there modern experiments which also have such a slow rate? What is the slowest rate of a modern experiment?

EDIT The following article claims that the modern experiment with the slowest rate is still 9 times as fast as that of Scripture. Is this really true?

• 4 $\begingroup$ If the current climate science stats are accurate, all frogs on earth are being heated at a rate of 0.2° C per decade, on average. Sure, there may be a few covariates to account for, but the sample size is huge . $\endgroup$ –  acvill Commented Mar 15, 2022 at 14:34
• 2 $\begingroup$ As noted in one of your links: "they don't sit still for you" seems to be the problem. If you put a frog in a pot, it doesn't matter if you heat it at all, if you allow them to escape they will escape. I kind of doubt anyone has actually published on that, though; people don't usually publish such trivialities. $\endgroup$ –  Bryan Krause ♦ Commented Mar 15, 2022 at 15:39
• 2 $\begingroup$ @Riemann It seems the modern commentators are saying that the frog doesn't need any temperature increase to escape. If you put a frog in a pot it will jump out if it can, heat or no heat, so they don't see the point to do the experiment with a gradual temperature change. Presumably in the original experiment (which I haven't read) the frog was not actually able to escape, otherwise it would have (again, not because of heat, but because of frogs doing frog things, like moving around freely when they can). $\endgroup$ –  Bryan Krause ♦ Commented Mar 15, 2022 at 16:34
• 4 $\begingroup$ OP: The most amazing of all your statements is that a dead frog jumped out of hot water! No wonder the experiment could not be reproduced! ("...a frog in water was heated very slowly. It didn't jump out until it died.") Like I said, that is one for the books. Or if one prefers journals, The Journal of Irreproducible Results . $\endgroup$ –  anongoodnurse Commented Mar 15, 2022 at 17:00
• 2 $\begingroup$ I don't really read enough German to read Heinzmann, but it seems that most, if not all, of his experiments were done in decerebrate frogs. It's a study of the reflex arc of the frog's leg and spine, rather than the behavior of the frog, from what I can tell. $\endgroup$ –  Bryan Krause ♦ Commented Mar 15, 2022 at 17:18

To clear up some things, I have made a partial answer here.

While it is old, you shouldn't discount the observations made by scientists from the 1800's. Many great scientists from this period laid the foundations for science as we know it now. These include names such as Charles Darwin, Alfred Wallace, Robert Koch, Gregor Mendel, and Louis Pasteur, to name a few well known biologists, whom no-one would think to doubt. Scientists in the 1800s were certainly exact in their measurements, observations and records, and I don't doubt that the observations that they made were exactly what they claimed they were.

To this end, I had a look at Goltz's 1869 book 1 (PDF here ) in the original German, and put it through Google translate ('cause I don't read German well enough to follow at this level) at the relevant point. Fortunately the PDF linked is text-selectable, so I was able to copy this directly and edit some minor misinterpretations from the paste. Google translate is pretty good for German and German has not changed significantly since the 1800's I believe.

Here's the bits I copied from pages 127 and 128 (you can see the errors at line-ends and in special characters, and where some bits can't be recognized as they are in the spine end of the text):

Von drei gleichzeitig gefangenen, gleich grossen und reiz- :en Fröschen schneide ich zweien mit der glühenden Platin- linge des galvanokaustischen Apparats die Köpfe ab. Dem tten sonst unversehrten blende ich die Augen, um unnütze will- 1 liehe Bewegungen desselben möglichst auszuschliessen. Darauf ce ich den zuletzt geköpften Frosch in ein weites blechernes iäss, dessen Boden mit mehreren Schichten Leinwand bekleidet und bringe ihn sogleich in die hockende Stellung, welche hirnte Frösche immer annehmen und dann nicht wieder von ')St verlassen. Das Gefäss fülle ich jetzt so weit mit Wasser, 'S nur ein kleiner Theil des Thieres daraus hervorragt. Zu 1 Enthaupteten setze ich dann den geblendeten Frosch, wel- r sich alsbald ebenfalls in hockender Stellung niederlässt und iangslos verharrt. Den zweiten Geköpften behalte ich in der le des Gefässes unter Augen. Jetzt fange ich an das Gefäss 128 Ueber den Sitz der Seele dea Frosches und zu erhitzen, die steigende Temperatur des Wassers an einem : dasselbe eingesenkten Thermometer ablesend. Die Zimmertempi ratur beträgt 17i”C. Hat das Wasser aber erst die Temperatur von 25“ erlangt, li verändert sich die Scene. Dem behirnten Frosch beginnt es uj behaglich zu werden. Er verändert den Ort, steckt den Kot weit zum Wasser hinaus, und fängt an, schneller zu athmen. j höher die Temperatur steigt, desto ängstlicher werden seine B< wegungen. Verzweiflungsvoll schwimmt das gequälte Thier ij Behälter umher, bald den Kopf weit hinausstreckend und imm< geschwinder nach Kühlung jappend, bald auf den Grund d< Gefässes tauchend, um dort der Pein zu entrinnen. Die Hita nähert sich gegen 38“. Das Thier macht verzweifelte Sprüng« um aus dem Behälter zu entkommen. Es klimmt an den glatte Wänden empor und muss in das heisse Wasser zurück gestosse werden. Die immer geschwinder auf- und niederfliegenden Atb mungsmuskeln erlahmen, die Athmung setzt aus. Immer wild^ werden die Schmerzensäusserungen, und endlich bei einer Teib peratur von etwa 42“ verendet das gequälte Thier unter tetan^ sehen Krämpfen.

And the translation:

I cut off the heads of two of three frogs of the same size and attractiveness that were caught at the same time with the glowing platinum pieces of the galvanocaustic apparatus. To the I blind the eyes of those who are otherwise undamaged in order to exclude useless voluntary movements as far as possible. Then I put the last decapitated frog in a wide tin vase, the floor of which was covered with several layers of canvas and immediately bring him into the squatting position, which brain frogs always accept and then not from again ')St leave. I fill the vessel with water now, 'S only a small part of the animal protrudes from it. to I then place the blinded frog on the decapitated one, which soon also settles down in a crouching position and fearless. I'll keep the second decapitated man in the le of the vessel under the eyes. Now I start the container, the water has reached a temperature of about 25", both frogs sit still in the warm bath. On the decapitated one sees the movements of the thighs, so common in decapitated people: he might pull one thigh up a little more or straighten a zoe, movements such as those used outside of the bath Lingering second decapitated also shows, which are therefore not dependent on the increasing temperature, and which incidentally will soon stopBut once the water has reached the temperature of 25", the scene changes. The brained frog begins to get uncomfortable. He changes the place, sticks the feces far out to the water, and begins to breathe faster. j the higher the temperature rises, the more anxious his movements become. The tormented animal ij swims in despair container around, soon stretching out the head far and imm Quickly yapping for coolness, soon to the bottom d vessel to escape from the torment there. the hita approaching around 38". The animal makes desperate leaps to escape from the container. It climbs to the smooth walls and has to be thrown back into the hot water will. The respiratory muscles, which fly up and down faster and faster, become slack and breathing stops. Always wild the expressions of pain become manifest, and finally at a body temperature of about 42" the tormented animal dies with tetanic convulsions.

You can see the bits, which the translator can't cope with - these are bits which didn't transcribe well, due to being in the spine of the book and not scanned properly. I also can't read these or even make a guess at what the proper word would be in many cases, though I have fixed those that I could. However, I think that the general text is largely fine to read and easy to interpret.

Basically, what Goltz did was attempt to study the nervous system and physiology of frogs. He did this by comparing decapitated or decerebrated frogs with intact ones (apart from blinded eyes, to exclude visual stimuli). He placed both of these in room temperature water and then heated it. When heated, the decapitated frogs did not show any reflex action and would sit still until dead unless stimulated by a different stimulus, which was some mild acetic acid applied to the back of the frog (bottom of page 128, not translated here). On the other hand, intact frogs would violently try to escape and would have to be placed back into the heated container, up to about 42 C, at which point they died.

Edited to add:

On page 130, there is a passage:

Behälter einen solchen, welchem ich das Gehirn mit einem qu Schnitt dicht vor den Sehhügeln abgetrennt hatte. Zu ihm s* ich einen geköpften Frosch, welchem ich die Hinterbeine i oben geschilderten Weise verschränkt hatte. Beide Frösche bli! ganz regungslos sitzen, bis die Temperatur des Wassers 32|'* reicht hatte. Da machte der hirnbesitzende Frosch mit dem eine Bewegung nach oben und fing an schneller zu athmen. 35“ machte er mit dem Körper eine kleine Wendung und sp dann plötzlich mit einem kräftigen Satz aus dem Behälter hii In’s Wasser zurückgebracht, machte er alsbald einen zweiten Sp> aus dem Geföss. Ausserhalb desselben wiederholte er die Hi bewegungen nie, sondern verharrte nach dem einen Satz, mit ehern er das Bad verlassen hatte, in Ruhe. Nachdem er, i: wieder in’s Bad zurückgebracht, im Ganzen sechs Sprünge g' hatte, und das Wasser inzwischen allmälig eine Hitze von erlangt hatte, starb er unter tetanischen Krämpfen. Während ser Scenen hatte der Geköpfte mit verschränkten Füssen ruhi gesessen. Bei 37?“ machte er die zuckenden Bewegungen, dij aussahen, als wenn er die verschränkten Füsse auseinander bri wollte. Bald wieder beruhigt, blieb er regungslos sitzen. Ui Zeit, als der Behirnte in Krämpfe verfiel, begann bei dem ^ köpften die Wärmestarre der Muskeln. Ohne dass die v schränkten Füsse sich lösten, wurden die Schenkel | allmälig etwas nach hinten gestreckt, und das ganze Thier hart und steif.

Translated:

Lately I have completed this experiment in the following way- changes; Instead of the blinded frog, I put one in the container, which I pierced the brain with a qu cut just before the brow mounds. To him a decapitated frog, whose hind legs i entangled in the manner described above. Both frogs bli! sit completely motionless until the temperature of the water is 32 had enough. Then the brain-possessing frog did that a movement upwards and began to breathe faster. 35” he made a small turn with his body and sp then suddenly with a powerful leap out of the container Brought back into the water, he immediately made a second spat from the vessel. Outside of this he never repeated the hi movements, but after one set he stayed with as soon as he had left the bath, in peace. After he had had six jumps in all when he was brought back into the bath, and the water was gradually getting hotter he died from tetanic convulsions. While The decapitated man had these scenes with crossed feet sat. At 37?” he made the twitching movements that looked like he was breaking his crossed feet apart wanted to. Soon calmed down, he sat motionless. wow Time when the crippled went into convulsions began at the beheaded the thermal rigidity of the muscles. Without the v when feet broke loose, the thighs were gradually stretched back a little, and the whole animal hard and stiff.

This is using frogs with their hind limbs crossed (and pinned?; see image page 103), so that they can no-longer swim properly and jump. The frog still gets out and is returned to water that is gradually getting hotter. Eventually it does not attempt to escape again. Note that the intact frog still tries to make movements and escape, just can't in the long run. I can only speculate on why it doesn't continue to try to escape, perhaps the water is too hot for proper function at this point, or perhaps it has learned that it can't escape, so gives up, which is a pretty sad conclusion to come to.

So, TL:DR - frogs try to escape when the water is too hot for them!

• Goltz F. 1869. Beitrāge zur lehre von de function der nervencentrum des frosches. Berlin.

• $\begingroup$ Thanks for the elaborate answer! This corresponds to what Wikipedia says about Friedrich Goltz's experiment. See en.wikipedia.org/wiki/Boiling_frog#Experiments_and_analysis $\endgroup$ –  Riemann Commented Mar 19, 2022 at 13:29
• $\begingroup$ However, according to Wikipedia, Heinzmann and Fratscher got results in which a normal frog did not jump out $\endgroup$ –  Riemann Commented Mar 19, 2022 at 13:30
• 1 $\begingroup$ @Riemann - you can track those publications down and have a look at them yourself. The author of the Wikipedia page obviously only looked at Sedgewick 1888, as they don't provide a reference for Fratscher. Heinzmann is in German, but translatable. Numerous experiments performed, but my German isn't good enough to read it, and I don't have the time to put in to translate it all. $\endgroup$ –  bob1 Commented Mar 20, 2022 at 20:51
• 1 $\begingroup$ I also haven't been able to track down Fratscher. All references come back to Sedgewick. $\endgroup$ –  bob1 Commented Mar 20, 2022 at 21:04

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The power of social influence: A replication and extension of the Asch experiment

Axel franzen.

Institute of Sociology, University of Bern, Bern, Switzerland

Sebastian Mader

Associated data.

The data used in this study is publicly available in the repository of the University of Bern at https://boris.unibe.ch/id/eprint/169645 .

In this paper, we pursue four goals: First, we replicate the original Asch experiment with five confederates and one naïve subject in each group (N = 210). Second, in a randomized trial we incentivize the decisions in the line experiment and demonstrate that monetary incentives lower the error rate, but that social influence is still at work. Third, we confront subjects with different political statements and show that the power of social influence can be generalized to matters of political opinion. Finally, we investigate whether intelligence, self-esteem, the need for social approval, and the Big Five are related to the susceptibility to provide conforming answers. We find an error rate of 33% for the standard length-of-line experiment which replicates the original findings by Asch (1951, 1955, 1956). Furthermore, in the incentivized condition the error rate decreases to 25%. For political opinions we find a conformity rate of 38%. However, besides openness, none of the investigated personality traits are convincingly related to the susceptibility of group pressure.

1. Introduction

A core assumption in sociology is that what humans think and do does not only depend on their own attitudes and disposition, but also to a large extent on what others think and do. The power of social influence on individuals’ behavior was demonstrated already in the 1950s in a series of experiments by Solomon Asch [ 1 – 3 ]. Asch invited individuals into the lab and assigned them the task of judging the length of a line. He also placed 6 confederates into the lab who were assigned to give wrong answers publicly, so that the naïve subject could hear them before he provided his own answer. The results were very surprising: on average 35% of the real subjects followed the opinions of the confederates even if their answer was obviously wrong. The work of Asch has attracted a great amount of attention in the social sciences. Hence, a multitude of replications, extensions, and variations of the original studies have been conducted. However, many of these replications were done with student samples in the US, and fewer studies consist of samples from other countries. Furthermore, many replications were undertaken in the 40 years following the original experiment of Asch, but there are fewer replications thereafter. This raises two important questions: First, are the findings of Asch universal or do they predominantly apply to American students? And second, are the findings still valid today or has the influence of others diminished over time, for instance through increased education and democratization?

Moreover, many experiments in psychology are not incentivized by monetary rewards. This is also true for Asch’s original experiments and for most replications of it. However, in real life outside the lab, decisions are usually associated with consequences, either pleasant in the form of rewards, or unpleasant in the form of some kind of punishment. To make the study of decision-making more realistic, experiments in economics usually use monetary incentives [ 4 ]. To provide a conforming but wrong judgment in the original Asch experiment has no consequences, giving rise to the interesting question of whether the finding of Asch still holds when correct answers are rewarded. So far, the effect of incentives in the Asch decision situation has only been investigated rarely [ 5 – 7 ], with inconclusive evidence. Baron et al. [ 5 ] report that use of monetary incentives actually increased conformity when the task was difficult. A decreased conformity rate was only found in situations with easy tasks. Bhanot & Williamson [ 6 ] conducted two online experiments and found that incentivizing correct answers increases the number of conforming answers. Fujita and Mori [ 7 ] compared group reward and individual rewards in the Asch experiment and found that conformity vanished in the individual reward condition. Thus, the existing evidence on the role of incentives is inconclusive, calling for further investigations of the effect of incentives.

Of course, misjudging the length of lines when others do is not important in itself; the Asch experiment created so much attention because it elicits the suspicion that social influence is also present in other and more important social realms, for instance when it comes to political opinions. Early research by Crutchfield [ 8 ] suggests that the original findings on line judgment also transfer over to political opinions. We are only aware of one further study by Mallinson and Hatemi [ 9 ] that investigates the effect of social influence on opinion formation. However, the authors used a group discussion in the treatment condition, and hence diverged somewhat from the original Asch design. Furthermore, investigations of the effect of social conformity on political opinions are always idiosyncratic making further replications on the transferability from lines to a variety of political opinions important and interesting.

Moreover, behaving in a conforming way and misjudging tasks raises a number of interesting questions. About one third of Asch’s subjects was susceptible to social pressure on average. The rest solved the task correctly irrespective of the confederates’ opinion most of the time. How do those who are not influenced by the group differ from the ones that behave in a conformative manner? Crutchfield [ 8 ] investigated a number of personality traits such as competence, self-assertiveness, or leadership ability on the susceptibility to the pressure to conform to the groups’ judgment. However, many of the measurement instruments used by him or by others [ 10 , 11 ] investigating similar questions are suboptimal, and furthermore produced inconclusive results. Hence, it is worthwhile to further investigate the characteristics of those who conform to social pressure and of those who resist it. We are particularly interested in the Big Five, intelligence, self-esteem, and the need for social approval.

The remainder of the article proceeds in four sections. First, in section two, we present an elaborate literature review of the original Asch experiment, and its various replications. Section three describes how we conducted the replication of the Asch experiment and its variant by using political opinions. Furthermore, we describe how we implemented the incentives, and how we measure the various traits that are presumably related to behavior in the Asch experiment. Section four presents the results and section five concludes and discusses ideas for further research.

2. Literature review

In Asch’s [ 2 ] original experiment 6 to 8 confederates gathered in an experimental room and were instructed to give false answers in matching a line with the length of three reference lines. An additional uninstructed subject was invited into the experimental room and asked to provide his judgment after the next to last of the confederates. Asch [ 2 ] reports a mean error rate of 36.8% of the 123 real subjects in the critical trials in which the group provided the wrong answer. This result was replicated remarkably consistently. Bond and Smith [ 12 ] conducted a meta study including 44 strict replications, and report an average error rate of 25%. As with the study by Asch [ 2 ], the vast majority of these replications were conducted with male university students in the US. However, more recent studies from Japan [ 13 , 14 ], and Bosnia and Herzegovina [ 15 ] also confirm Asch’s findings. Takano and Sogon [ 14 ] found an error rate of 25% in male Japanese university students (n = 40) in groups with 6 to 9 confederates. Mori and Arai [ 13 ] used the fMORI technique in which participants wear polarized sunglasses allowing the perception of different lines from the same presentation. The method allows to abandon the use of confederates in the Asch judgment task. They replicated the conformity rate for Japanese female subjects (N = 16) but found no conformity for male subjects (N = 10). Usto et al. [ 15 ] found an error rate of 35% in 95 university students of both sexes from Bosnia and Herzegovina with five confederates per group. Other studies also show that subjects are influenced by groups, when the confederates provided their judgments anonymously or with respect to different judgment tasks such as judging the size of circles, completing rows of numbers, or judging the length of acoustic signals [ 8 , 12 , 16 – 21 ]. More recent studies conducted the Asch experiment also with children [ 22 – 25 ] suggesting that the conformity effect can also be found in preschool children. However, some studies also found age effects, such that younger children conformed to the groups majority judgment, but the effect decreases for adolescents [ 26 , 27 ]. To summarize, given the results of the literature, we expect to find a substantial conformity rate in the replication of the original Asch line experiment (H 1 ).

2.1 Monetary incentives

An important extension of the original Asch experiment is the introduction of incentives. In everyday life, decisions are usually associated with consequences. However, in the Asch experiment, as in many other experiments in psychology, decisions or behavior in the lab usually have no consequences, besides of standing out in the laboratory group. This raises questions of the external validity of non-incentivized experiments. Theoretically, it can be expected that correct judgments are less important if they are not incentivized. This could imply that the findings of the Asch experiment are partly methodological artifacts. So far there is only limited and inconclusive empirical evidence with respect to monetary incentives in the Asch experiment. Early studies analysed the role of the perceived societal or scientific importance of the task [ 20 ]. Later research incentivized correct answers in various conformity experiments. Andersson et al. [ 28 ] report that individual incentives decreased the effect of conformity on the prediction of stock prices. However, Bazazi et al. [ 29 ] report the opposite. They found that individualized incentives increase conformity in comparison to collective payoffs in an estimation task. In the study of Baron et al. [ 5 ] 90 participants solved two eyewitness identifications tasks (a line-up task and a task of describing male figures) in the presence of two unanimously incorrectly-answering confederates. Additionally, task importance (low versus high) and task difficulty (low versus high) were experimentally manipulated resulting in a 2 x 2 between subject design. Subjects in the high task importance condition received $20 if ranked in the top 12% of participants with regard to correct answers. Subjects in the low task importance condition received no monetary incentive for correct answers. The results of Baron et al. [ 5 ] show a conformity rate that closely replicates Asch’s [ 1 – 3 ] finding in the condition without monetary incentives. In the condition including a monetary incentive for correct answers, conformity rates drop by about half to an error rate of 15%. However, this result only emerges in the condition with low task difficulty. For the high task difficulty condition, the opposite effect of monetary incentives was observed. Thus, monetary incentives increased conformity when the task was difficult and decreased conformity in situations with easy tasks. However, one drawback of the study of Baron et al. [ 5 ] is a rather low sample size, which might explain the differential effects by experimental condition.

Fujita and Mori [ 7 ] analysed the effect of individual vs collective payoff in the Asch experiment. They found that the conformity effect disappears in the individually incentivized condition. However, also this study suffered from low sample sizes since there were only 10 subjects in the individualized minority incentive condition. Furthermore, Fujita and Mori [ 7 ] used the fMORI method and report that some subjects might have noticed the trick.

Bhanot and Williamson [ 6 ] conducted online experiments (using Amazon Mechanical Turk) in which 391 participants answered 60 multiple-choice trivia-knowledge questions while the most popular answer was displayed at each question. Correct answers were incentivized randomly with $0, $1, $2 or $3 each in a within-subject design, i.e. randomized over trials, not over subjects. Bhanot and Williamson [ 6 ] found that monetary incentives increase the proportion of answers that align with the majority. Hence, the studies using incentives yield inconclusive and contradicting results: Particularly, Baron et al. [ 5 ] found both an accuracy-increasing and accuracy-decreasing effect of monetary incentives depending on task difficulty. Bhanot and Williamson [ 6 ] found an increased conformity rate, and Fujita and Mori [ 7 ] found that the conformity bias disappears in the individually incentivized condition. Overall, we follow the economic notion that monetary incentives matter and expect that rewards for nonconformity decrease group pressure (H 2 ).

2.2 Political opinions

Another critical question is, whether matters of fact can be generalized to matters of attitude and opinion. Crutchfield [ 8 ] investigated experimentally the influence of social pressure on political opinions in an Asch-like situation. He found that agreement with the statement “Free speech being a privilege rather than a right, it is proper for a society to suspend free speech whenever it feels itself threatened” was almost 40 percentage points higher in the social pressure condition (58%, n = 50) than in the individual judgment condition (19%, n = 40). Furthermore, he observed a difference of 36%-points if the confederates answer “subversive activities” to the question "Which one of the following do you feel is the most important problem facing our country today? Economic recession, educational facilities, subversive activities, mental health or crime and corruption” as compared to an individual judgment condition (48% vs 12%). However, the results are based on a rather small number of cases and decisions were anonymous, unlike the original design of Asch.

To the best of our knowledge, there is only one further study that experimentally investigates the influence of social pressure on opinions regarding political issues in an Asch-like situation. In the study of Mallinson and Hatemi [ 9 ] participants (n = 58) were asked to give their opinion on a specific local political issue before and after a 30–45 minutes face-to-face group discussion (treatment condition). In the control condition subjects received written information that contradicts their initial opinion. They found that in the control condition only 8% changed their initial opinion when provided with further information, while in the treatment condition 38% of subjects changed their opinion. Yet, in this recent study the sample size is also rather small. To sum up, given the results of these two studies, we expect that groups exert influence also on political opinions (H 3 ).

2.3 Individual differences

Crutchfield [ 8 ] was also the first who investigated the relationship between personality traits and the susceptibility to the pressure of conformity. He found that low conformity rates were related to high levels of intellectual competence, ego strength, leadership ability, self-control, superiority feelings, adventurousness, self-assertiveness, self-respect, tolerance of ambiguity, and freedom from compulsion regarding rules. High levels of conformity were observed for subjects with authoritarian, anxious, distrustful, and conventional mindsets. However, no substantial correlation was found for neuroticism. Obviously, Crutchfield’s [ 8 ] study is limited by a rather low number of subjects (N = 50). Moreover, the measurement instruments used may be debatable from a contemporary point of view. We are aware of one more recent study with a sufficiently high number of study subjects and more rigid measurement instruments to test the influence of personality traits on conformity in Asch-like situations: Kosloff et al. [ 19 ] analysed the association of the Big Five personality traits (agreeableness, conscientiousness, extraversion, neuroticism, and openness) with conformity in public ratings of the humorousness of unfunny cartoons in 102 female college students. Kosloff et al. [ 19 ] found that subjects with low neuroticism, high agreeableness, and high conscientiousness scores show high levels of conformity. Extraversion, and openness were not associated with conformity ratings. Beyond that, we are not aware of any more studies that investigate the influence of the Big Five personality traits in the original Asch situation. However, there is evidence that openness is linked to nonconformity. Eck and Gebauer [ 30 ] argue that “open people engage in independent thought and, thus, rely little on the conformity heuristic”.

Crutchfield [ 8 ] studied the effect of intellectual competence on conformity. He found that higher competence was associated with lower levels of conformity. However, intelligence was measured by the subjective ratings of the experimental staff. Iscoe, Williams, and Harvey [ 10 ] exposed high school students (7 to 15 years) to group pressure in an acoustic task (counting metronome ticks), and approximated intelligence by subjects’ school records. They found no correlation of school records with conformity. Uchida et al. [ 31 ] studied 12 to 14 year-old high school students and assessed scholastic achievements by their school performance. They report that high achievers conformed less to the majority than low achievers. Hence, results of the effect of intelligence on conformity are inconclusive so far and the existing studies use indirect measures (school grades) but do not measure intelligence directly.

The effect of self-esteem (or self-assertiveness, self-consciousness) on conformity was only investigated in a few studies so far. Kurosawa [ 11 ] found no effect on conformity when the decision of the minority subject was preceded by two confederates. In groups of four, confederates’ self-esteem had a negative effect on conformity. Similarly, Tainaka et al. [ 32 ] found in a sample of Japanese female students that those with low self-esteem conformed more often in a co-witness task.

In addition, the need for social approval may explain individual differences in conformity behavior. The urge to please others by adhering to social norms is expected to be positively related to conformity, simply because conformity is socially approved in many situations and because of a general tendency among humans toward acquiescence. Once more, Crutchfield [ 8 ] provided the first hints of a positive relationship between the need for social approval and conforming behavior in an anonymous Asch situation. However, the measurement instrument he used is debatable. Strickland and Crowne [ 33 ] confirmed Crutchfield’s [ 8 ] finding in a sample of 64 female students exposed to an Asch-like acoustic judgment task using the Crowne-Marlowe (CM) social desirability scale [ 34 , 35 ] to gauge the need for social approval. Again, we are not aware of any other more recent study on this aspect. Hence, we investigate the association of the need for social approval using the CM social desirability scale as well as a more recent and supposedly more appropriate instrument to capture the need for social approval [ 36 ]. Summarizing, we expect to find a positive association between social approval and conformity (H 4 ), and negative associations for intelligence (H 5 ) and self-esteem (H 6 ). With respect to the Big Five we follow Eck and Gebauer [ 30 ] and expect a negative relation between openness and conformity (H 7 ).

Finally, Crutchfield [ 8 ] also analysed the influence of gender on conformity in a sample of 40 female and 19 male college students (study two). He found that young women show higher conformity rates than young men. Yet, in a third study he found that female college alumnae (N = 50) show lower conformity rates than in study one. Hence, Crutchfield’s [ 8 ] findings for the gender effect are inconclusive. However, Bond and Smith [ 12 ] report in their meta-analysis higher conformity rates for females. The study by Griskevicius et al. [ 18 ] shows that gender-differences in conformity depend on the activation of behavioral motives. Men who were primed to attract a mate revealed more independent judgments than women primed to attract a mate, supposedly because of differing mating preferences in men and women. Therefore, we wonder, whether we can replicate the finding that females are more conformative than males in the Asch experiment.

3. Design and method

3.1 procedure and materials.

The experiment consisted of three parts. Part 1 was designed to replicate the original Asch experiment. For this purpose, we recruited 210 subjects on the campus of the University of Bern. Informed consent was obtained verbally before participants entered the experimental room. We randomized subjects into two groups. In group one subjects had to judge the length of lines, as in the original Asch experiment. For this purpose, we placed 5 confederates in addition to a naïve subject in a room. The confederates were asked to behave as naïve subjects and entered the room one after the other. The front row of the seats in the experimental room were numbered such that subjects sat next to each other. The naïve subject was always assigned to seat number 5, leaving the last seat to another confederate. First, we presented some instructions to the subjects: “Welcome to our study on decision-making behavior and opinions. This study consists of two parts: In the first part in this room, we ask you to solve a total of 10 short tasks. In the second part in the room next door, we ask you to complete a short questionnaire on the laptop. In total, this study takes about 40 minutes. As compensation for your participation, you will receive 20 Swiss francs in cash after completing the study.” We then presented a reference line to subjects next to three other lines that were numbered 1 through 3 on projected slides. Subjects were asked to judge the length of the reference line by naming the number of the line that corresponds to the reference line in length. We presented 10 such line tasks (see Fig A1 in the S1 Appendix ). In the first two trials as well as in trials number 4 and 8, confederates pointed out the correct lines. Four trials were easy tasks, since the difference between the reference line and two of the other lines was large. The other six trials were more difficult, since the differences were small. Subjects were asked to call out the number of the correct line always starting with subject 1 through 6.

After the line task in part 2 of the experiment subjects were confronted with 5 general questions on different political issues. The statements were selected because we believe they describe fundamental attitudes towards different political or social groups in a democracy. The five statements read (1) “Do you think that the Swiss Federal Government should be given more power?”, (2) “Do you think trade unions should be given more power in Switzerland?”, (3) “Do you think that the employers’ association in Switzerland should be given more power?”, (4) “Do you think that citizens should be given more liberties in Switzerland?”, and (5) “Do you think that companies in Switzerland should be given more freedom?”. Subjects were asked to answer all 5 questions with either yes or no. The confederates in this group were instructed to answer “yes” to the first question and “no” to the rest. We chose this sequence of “yes” and “no” to prevent that subjects discover the existence of confederates. Finally, part 3 of the experiment consisted of an online questionnaire which subjects were asked to complete. To conceal that some participants were confederates all 6 participants were accompanied to separate rooms where the online-questionnaire was installed on a laptop. The questionnaire was designed to measure a number of different personality traits. Particularly, we measured the Big Five using a 10-item scale (two items for each of the 5 traits) as suggested by Rammstedt et al. [ 37 ] (see Table A1 in the S1 Appendix for item wording); a 10-item scale measuring self-esteem as suggested by Rosenberg [ 38 ] (see Table A2 in the S1 Appendix ); a short version of the Hagen Matrices Test [ 39 ] to measure intelligence and the 10-item version of the Martin Larson Approval Motivation Scale (MLAM) [ 36 ].

In group 2 the experimental design and procedure was the same as in group 1 besides the fact that correct answers in the length of lines judgment task were incentivized. In addition to the 20 Swiss francs show-up fee, subjects received one Swiss franc for every correct answer in the line judgment task, and hence, could earn up to 30 Swiss francs in total. Since there are no correct answers to political opinions these were not incentivized. However, we randomized the confederates’ answers to political opinion questions independently of whether a subject was in the incentivized or non-incentivized group. In one version confederates answered “yes” to the first question and “no” to the four other questions. In the other version the sequence of the confederates’ response was “no” to the first question and “yes” in response to the other four. The experiment was conducted by three different research teams consisting of 7 student assistants each. In every group 5 students acted as confederates and 2 as research assistants, recruiting subjects, welcoming and instructing them in the laboratory room, and reading out loud the projected instructions.

A power analysis suggested that we need about 100 subjects per experimental condition to find statistically significant (α = 0.05) differences of 5 percentage points for a power of 0.8. Hence, we stopped recruiting subjects after reaching 210 participants. The experiment was conducted between March 16, 2021 and April 30, 2021. The authors had no access to any information that links individual identifiers to the data. Subjects were debriefed after the end of the study by email.

Overall, 210 subjects participated in the experiment (female = 61%, mean age = 22.6). 102 subjects were randomly assigned to the non-incentivized group and 108 into the group with incentives. Moreover, 113 subjects were assigned to the sequences of “yes” and four “no” of the political opinion task and 97 to the reversed sequence, suggesting that the randomization procedure worked well. The questionnaire also contained an attention check. The question reads “In the following we show you five answer categories. Please do not tick any of the answers”. Four subjects failed to comply and ticked an answer, suggesting that they did not pay proper attention to the question wording. These subjects were excluded from the analysis. Furthermore, we asked subjects at the end of the questionnaire what they think the experiment was about. Three subjects recognized that the experiment was the line task experiment of Asch or expressed the suspicion that some of the other group members were confederates. We also excluded these three subjects from the analysis. Moreover, one subject answered the question about their gender with “other” and was also excluded from the analysis. Hence, these exclusions result in 202 valid cases. However, the results presented do not depend on these eight excluded observations.

Fig 1 presents the results of the ten line length tasks for the non-incentivized (grey bars) and for the incentivized conditions (blue bars). As can be clearly seen, almost none of the naïve subjects gave an incorrect answer when the group provided the correct answer which was the case in decision situations 1, 2, 4 and 8. However, when the group provides the false answer a substantial number of naïve subjects provided this incorrect answer as well (decision situations 3, 5, 6, 7, 9, and 10). The proportion of incorrect answers in the non-incentivized condition is relatively small in decision 3 (10%), but relatively high in decisions number 6 and 7 (44% and 47%). The average of incorrect answers is 33% in the non-incentivized group, which is a perfect replication of Asch’s (1955) original 36.8% result (two sample two-sided T-test, t(16) = 0.59, p = 0.57).

Note: Percent of correct answers by experimental group and trial including 95% confidence intervals. The numbers on top of the bars denote the trial numbers. “correct” stands for uncritical trials, “false” for critical trials. “easy” denotes easy trials with big differences between the lines, and “hard” denotes more difficult trials with smaller differences between the lines. The numbers between the bars denote the difference in proportions between the groups in percentage points. One-sided T-tests: * = p < 0.05. N without incentive (no) = 99, n with incentive (yes) = 103.

When correct answers are incentivized, the proportion of incorrect answers decreases by on average 8%-points. The difference between the groups is statistically significant in 2 out of 6 critical trials (p < 0.05 for one-sided T-tests). The difference also becomes evident when we consider the number of incorrect answers in the 6 critical trials. When decisions were not incentivized subjects gave on average 1.97 incorrect answers. In the incentivized condition the average number dropped to 1.47, leading to a statistically significant difference of 0.5 incorrect answers (t(208) = 2.24, p = 0.03 for two-sided T-test).

Next, Fig 2 presents the results concerning the five political questions. When the group said “yes” to the question of whether the Swiss Federal Council (the government in Switzerland) should have more power, 27% of the naïve subjects did so as well. When the group said “no” only 3% of the subjects said “yes” resulting in a difference of 23.4%-points. When the group said that trade unions should have more power 72% of the subjects answered “yes” as compared to only 29% when the group said “no” resulting in a difference of 43%-points. Similarly, the question of whether the employers’ association should have more power is agreed to by 44% and 6% respectively, depending on the group agreeing or disagreeing. Moreover, 81% of the subjects agreed that citizens in Switzerland should be given more liberties when the group does so, and 33% agreed to this question when the group says “no”. Finally, 46% said that companies should be given more freedom when the group agreed but only 8% did so when the group denied this question. The average difference in the proportion of yes-answers is 38%-points and all 5 differences are statistically highly significant. This result corresponds astonishingly close to the result in the length of line experiment and suggests that the influence of group pressure can be generalized to the utterance of political opinions.

Note: Percent of ‘yes’ answers to five general questions on political opinions in which all confederates answered uniformly ‘yes’ or ‘no’, by experimental group including 95% confidence intervals. The numbers on top of the bars stand for the difference in proportions between the respective groups in percentage points. Two-sided T-tests: *** = p < 0.001. n (sequence yes, no, no, no, no) = 109, n (sequence no, yes, yes, yes, yes) = 93.

One interesting question is whether the susceptibility to group pressure is linked to certain personality traits. To investigate this question, we count the number of wrong answers in the six critical trials of the length of line task. This variable is our dependent variable and runs from 0 when a subject always gave correct answers to 6 for subjects who gave only wrong answers. First, we wondered whether conformity is linked to the Big Five personality traits. We measured the Big Five using a short 10-item version as suggested by Rammstedt et al. [ 37 ] which measures each trait (openness, extraversion, agreeableness, conscientiousness, and neuroticism) with two questions (see Table A1 in the S1 Appendix ).

Second, we incorporate a 10-item measure of self-esteem, as suggested by Rosenberg [ 38 ], into the analysis (see Table A2 in the S1 Appendix ). Each item of the scale has four answer categories ranging from 1 = “disagree strongly”, 2 = “disagree”, 3 = “agree” to 4 = “agree strongly”. Subjects that score high on self-esteem are expected to have stronger confidence in their own perception and should be less influenced by the group’s opinion. Third, we measured individuals’ intelligence using a short version of the Hagen Matrices Test (HMT) [ 39 ]. The HMT consists of six 9-field matrices that show graphical symbols that follow a logical order. The last field is missing and the task of the subjects is to pick the correct symbol, out of eight, that fits and completes the pattern of the matrix. Hence, the HMT ranges from 0 if no answer is correct to 6 for subjects who provided six correct answers. The hypothesis is that subjects who score high on the HMT are less susceptible to the pressure of the group and also provide more correct answers in the line task.

Finally, conformity might be linked to the need for social approval. We measured the need for social approval with a 10-item version of the Martin Larson Approval Motivation Scale (MLAM) [ 36 ] (see Table A3 in the S1 Appendix ). Individuals that score highly on the MLAM display high need for social approval by others. Hence, we expect that subjects with higher values on the MLAM should also conform more often to the opinions of others in order to receive social approval. A summary of the descriptive information of the considered variables is depicted in Table A4 in the S1 Appendix . To investigate whether any of the measured personality traits are linked to the answering behavior in the line task we conducted multiple OLS regression analysis. The results of this analysis are depicted in the coefficient plots in Fig 3 (see also Table A5 in the S1 Appendix ).

Note: N = 202. Unstandardized coefficients of multiple linear OLS regressions including robust 95% confidence intervals. Poisson and negative binomial models do not alter the results in any substantial way. Variables marked with an ‘*’ indicate statistically significant differences in the coefficients between models (2) and (3).

First, model 1 presents the effects on the number of conforming answers for the whole sample. In the incentivized condition subjects gave on average 0.43 fewer conforming answers as compared to the unincentivized condition. This effect mirrors the bivariate result already presented in Fig 1 and is statistically significant for the 5% level. In tendency, females show more conforming answers, but this effect is statistically only significant for the 10% level. Besides “openness” none of the personality traits contained in the Big Five show any statistically significant effects. This is also true for the other effects of intelligence, self-esteem, and the measure for social approval seeking. Models 2 and 3 show the results for men and women separately. The separate results suggest that women react somewhat more strongly to incentives than do men. However, a test for differences in coefficients suggests that the effects do not differ (χ 2 (1) = 1.11, p = 0.29). Intelligence seems to have greater importance for men, leading to 0.27 fewer conforming answers for every correct answer of the HMT. However, this effect does not differ statistically from the effect for females (χ 2 (1) = 1.35, p = 0.25). No difference in effects can be observed for self-esteem. However, in the female sample the need for social approval is positively linked to the number of conforming answers, which is not the case in the male sample (χ 2 (1) = 4.23, p = 0.04); but the effect of social approval in the female sample is relatively small.

We conducted a number of robustness checks with the presented analyses. Since our dependent variable is a count variable (number of conforming answers) the models can also be estimated using Poisson regressions or negative-binomial models. However, none of our presented results change in any substantial way using these alternatives. Furthermore, we excluded 24 more subjects who when asked at the end of the experiment about the goal of the study said that the experiment was about group pressure or conformity, although they did not explicitly mention Asch or the suspicion that other participants were confederates. But these additional exclusions also did not change the results substantially (see Table A6 in the S1 Appendix ). Finally, we also incorporated the 10-item version of the Marlowe-Crowne Scale [ 34 , 35 ] suggested by Clancy [ 40 , 41 ]. However, inclusion of the scale did not show any statistically significant effects or did change any of the other estimates.

5. Conclusion and discussion

In this study we first replicated the original experiment of Asch [ 1 – 3 ] with 5 confederates and ten line tasks. We find an average error rate of 33% which replicates the original findings of Asch very closely and which is in line with other replications that were conducted predominately with American students [ 12 ]. Together with recent studies from Japan [ 14 ], and Bosnia and Herzegowina [ 15 ], our study provides further evidence that the influence of groups on individuals’ judgments is a universal phenomenon, and is still valid today. Furthermore, we incentivized the decisions and find a drop of the error rate by 8%-points to 25%. Hence, monetary incentives do not eliminate the effect of group pressure. This finding sheds doubt on former results which predominately show the opposite effect, namely that incentives increase compliance [ 5 , 6 ].

Moreover, our study suggests that group pressure is not only influential in the simple line task but also when it comes to political opinions. We randomized the groups’ response to five different political statements and find an average conformity rate of 38%. Hence, these results suggest that the original finding of Asch can also be generalized to matters of opinion. This result is in line with former evidence by Crutchfield [ 8 ], and Mallinson and Hatemi [ 9 ]. However, both of these studies had only small sample sizes of 50 and 58 subjects respectively, which called for further replication studies. Finally, we measured the Big Five, intelligence, self-esteem and social approval. With the exception of openness, our study finds no support that these personality traits are statistically significantly related to the susceptibility of group pressure.

Of course, our study has some limitations, which suggest a number of further research questions. First, we used a relatively large sample of 202 subjects providing more statistical power than former replications and extensions of the Asch experiment; however, our subjects were also students, and hence, it would be important to have further replications with non-student samples. This would allow further investigations of the susceptibility to group pressure with respect to age, different occupational groups, different social backgrounds, and different levels of social experience.

Second, the subjects we investigate are strangers. That means the single naïve subjects did not know the confederates. An interesting question for further research would be, whether group pressure is stronger among non-strangers or whether dissent becomes more acceptable among a group of friends.

Third, we demonstrate that monetary incentives reduce the error rate. However, our incentives were one Swiss franc for every correct answer, and hence small. Thus, the interesting question remains whether larger incentives reduce the error rate further, or can even lead to the elimination of it.

Fourth, the political statements we choose are relatively moderate and general. This leaves the question open as to whether subjects would also conform to more extreme or socially less acceptable statements. Furthermore, our subjects might have rarely thought about the statements we provided, leaving the question of what would happen with respect to statements about which subjects had stronger opinions or which are more related to their identity.

With the exception of openness all personality traits considered (e.g. intelligence, self-esteem, need for social approval) are not related to conformity. This raises a number of very interesting research questions. One possibility is that the traits were not measured good enough, and that measurement errors impede the identification of these individual differences. This concern applies particularly to the measurement of the Big Five where we relied on the short 10-item version suggested by Rammstedt et al. [ 37 ]. Hence, the puzzling result that openness leads to less conformity must be replicated before it can count as a reliable finding. However, the finding is in line with the assumption of Eck and Gebauer [ 30 ]. Another possibility is that other personality traits are more important when it comes to conformity behavior. Hence, there is much room for further interesting research concerning conformity behavior in situations of group pressure.

Supporting information

S1 appendix, acknowledgments.

We like to thank our student assistants for helping us with the data collection. Their names are: Yvonne Aregger, Elias Balmer, Ambar Conca, Davide Della Porta, Shania Flück, Julian Gerber, Anna Graf, Ina Gutjahr, Kim Gvozdic, Anna Häberli, Chiara Heiss, Paula Kühne, Jenny Mosimann, Remo Parisi, Elena Raich, Virginia Reinhard, Fiona Schläppi, Maria Tournas, Angela Ventrici, Marco Zbinden, Sarah Zwyssig.

Funding Statement

The author(s) received no specific funding for this work.

Data Availability

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