This article describes how empirical discoveries in the 1930s–1950s regarding population variation for chromosomal inversions affected Theodosius Dobzhansky and Richard Goldschmidt. A significant fraction of the empirical work I discuss was done by Dobzhansky and his coworkers; Goldschmidt was an astute interpreter, with strong and unusual commitments. I argue that both belong to a mechanistic tradition in genetics, concerned with the effects of chromosomal organization and systems on the inheritance patterns of species. Their different trajectories illustrate how scientists’ commitments affect (...) how they interpret new evidence and adjust to it. Dobzhansky was moved to revised views about selection, while Goldschmidt moved his attention to different genetic phenomena. However different, there are significant connections between the two that enrich our understanding of their views. I focus on two: the role of developmental considerations in Dobzhansky’s thought and the role of neutrality and drift in Goldschmidt’s evolutionary account. Dobzhansky’s struggle with chromosomal variation is not solely about competing schools of thought within the selectionist camp, as insightfully articulated by John Beatty, but also a story of competition between selectionist thinking and developmental perspectives. In contraposition, Goldschmidt emphasized the role of low penetrance mutations that spread neutrally and pointed out that drift could result from developmental canalization. This account adds to the dominant story about Goldschmidt’s resistance to the splitting of development from genetics, as told by Garland Allen and Michael Dietrich. The story I tell illustrates how developmental thinking and genetic thinking conflicted and influenced researchers with different convictions about the significance of chromosomal organization. (shrink)

This article considers the reception of British cytogeneticist C.D. Darlington's controversial 1932 book, Recent Advances in Cytology. Darlington's cytogenetic work, and the manner in which he made it relevant to evolutionary biology, marked an abrupt shift in the status and role of cytology in the life sciences. By focusing on Darlington's scientific method -- a stark departure from anti-theoretical, empirical reasoning to a theoretical and speculative approach based on deduction from genetic first principles -- the article characterises the relationships defining (...) the "disciplinary landscape" of the life sciences of the time, namely those between cytology, genetics, and evolutionary theory. (shrink)

This article considers the reception of British cytogeneticist C.D. Darlington's controversial 1932 book, Recent Advances in Cytology. Darlington's cytogenetic work, and the manner in which he made it relevant to evolutionary biology, marked an abrupt shift in the status and role of cytology in the life sciences. By focusing on Darlington's scientific method -- a stark departure from anti-theoretical, empirical reasoning to a theoretical and speculative approach based on deduction from genetic first principles -- the article characterises the relationships defining (...) the "disciplinary landscape" of the life sciences of the time, namely those between cytology, genetics, and evolutionary theory. (shrink)

This paper gives a detailed narrative of a controversial empirical research in postwar population genetics, the analysis of the cytological polymorphisms of an Australian grasshopper, Moraba scurra. This research intertwined key technical developments in three research areas during the 1950s and 1960s: it involved Dobzhansky’s empirical research program on cytological polymorphisms, the mathematical theory of natural selection in two-locus systems, and the building of reliable estimates of natural selection in the wild. In the mid-1950s the cytologist Michael White discovered an (...) interesting case of epistasis in populations of Moraba scurra. These observations received a wide diffusion when theoretical population geneticist Richard Lewontin represented White’s data on adaptive topographies. These topographies connected the information on the genetic structure of these grasshopper populations with the formal framework of theoretical population genetics. As such, they appeared at the time as the most successful application of two-locus models of natural selection to an empirical study system. However, this connection generated paradoxical results: in the landscapes, all grasshopper populations were located on a ridge while they were expected to reach a peak. This puzzling result fueled years of research and triggered a controversy attracting contributors from Australia, the United States and the United Kingdom. While the original problem seemed, at first, purely empirical, the subsequent controversy affected the main mathematical tools used in the study of two-gene systems under natural selection. Adaptive topographies and their underlying mathematical structure, Wright’s mean fitness equations, were submitted to close scrutiny. Suspicion eventually shifted to the statistical machinery used in data analysis, reflecting the crucial role of statistical inference in applied population genetics. In the 1950s and 1960s, population geneticists were not simply in search for new generalizations about the evolutionary process and for new evidence about genetic variation: struggling against statistical artifacts, they were searching for reliable tests and descriptors to analyze their data. (shrink)

Genetics was established on a strict particulate conception of heredity. Genetic linkage, the deviation from independent segregation of Mendelian factors, was conceived as a function of the material allocation of the factors to the chromosomes, rather than to the multiple effects (pleiotropy) of discrete factors. Although linkage maps were abstractions they provided strong support for the chromosomal theory of inheritance. Direct Cytogenetic evidence was scarce until X-ray induced major chromosomal rearrangements allowed direct correlation of genetic and cytological rearrangements. Only with (...) the discovery of the polytenic giant chromosomes in Drosophila larvae in the 1930s were the virtual maps backed up by physical maps of the genetic loci. Genetic linkage became a pivotal experimental tool for the examination of the integration of genetic functions in development and in evolution. Genetic mapping has remained a hallmark of genetic analysis. The location of genes in DNA is a modern extension of the notion of genetic linkage. (shrink)

The encounter between the Darwinian theory of evolution and Mendelism could be resolved only when reductionist tools could be applied to the analysis of complex systems. The instrumental reductionist interpretation of the hereditary basis of continuously varying traits provided mathematical tools which eventually allowed the construction of the Modern Synthesis of the theory of evolution.When genotypic as well as environmental variance allow the isolation of parts of the system, it is possible to apply Mendelian reductionism, that is , to treat (...) the phenotypic trait as if ti causally determined by discrete genes for the trait. howeverm such a beanbag genetics approach obscures the system's eye-view. The concept of heritability, defined as the proportion of the total phenotypic variance due to (additive) hereditary variation, asserts that genetic elements have discrete effects; but by relating to the genotypic variance, it avoids the trap of reffering to genes for characters. (shrink)

In the 1960s molecular population geneticists used Monte Carlo experiments to evaluate particular diffusion equation models. In this paper I examine the nature of this comparative evaluation and argue for three claims: first, Monte Carlo experiments are genuine experiments: second, Monte Carlo experiments can provide an important meansfor evaluating the adequacy of highly idealized theoretical models; and, third, the evaluation of the computational adequacy of a diffusion model with Monte Carlo experiments is significantlydifferent from the evaluation of the emperical adequacy (...) of the same diffusion model. (shrink)

In the early twentieth century, Tatsuo Aida in Japan, Øjvind Winge in Denmark, Richard Goldschmidt in Germany, and Calvin Bridges in the United States all developed different experimental systems to study the genetics of sex reversal. These locally specific experimental systems grounded these experimenters’ understanding of sex reversal as well as their interpretation of claims regarding experimental results and theories. The comparison of four researchers and their experimental systems reveals how those different systems mediated their understanding of genetic phenomena, and (...) influenced their interpretations of sex reversal. (shrink)

The reductionistic vision of evolutionary theory, "the gene's eye view of evolution" is the dominant view among evolutionary biologists today. On this view, the gene is the only unit with sufficient stability to act as a unit of selection, with individuals and groups being more ephemeral units of function, but not of selection. This view is argued to be incorrect, on several grounds. The empirical and theoretical bases for the existence of higher-level units of selection are explored, and alternative analyses (...) discussed critically. The success of a multi-level selection theory demands the recognition and development of a multi-level genetics. The way to accomplish this is suggested. The genotype/phenotype distinction also requires further analysis to see how it applies at higher levels of organization. This analysis provides a way of defining genotype and phenotype for cultural evolution, and a treatment of the innate-acquired distinction which are both generalizeable to analyze problems of the nature and focus of scientific change. (shrink)