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)

I propose we abandon the unit concept of "the evolutionary synthesis". There was much more to evolutionary studies in the 1920s and 1930s than is suggested in our commonplace narratives of this object in history. Instead, four organising threads capture much of evolutionary studies at this time. First, the nature of species and the process of speciation were dominating, unifying subjects. Second, research into these subjects developed along four main lines, or problem complexes: variation, divergence, isolation, and selection. Some calls (...) for 'synthesis' focused on these problem complexes (sometimes on one of these; other times, all). In these calls, comprehensive and pluralist compendia of plausibly relevant elements were preferred over reaching consensus about the value of particular formulae. Third, increasing confidence in the study of common problems coincided with methodological and epistemic changes associated with experimental taxonomy. Finally, the surge of interest in species problems and speciation in the 1930s is intimately tied to larger trends, especially a shifting balance in the life sciences towards process-based biologies and away from object-based naturalist disciplines. Advocates of synthesis in evolution supported, and were adapting to, these larger trends. (shrink)