Descended from Darwin

Introduction Recently, much philosophical discussion has centered on the best way to characterize the concepts of random drift 1 and natural selection, and, in particular, whether selection and drift can be conceptually distinguished 2 These authors all contend, to a greater or lesser degree, that their concepts make sense of biological practice. So it should be instructive to see how the concepts of drift and selection were distinguished by the disputants in a high-profile debate; debates such as these often force biologists to take a more philosophical turn, discussing the concepts at issue in greater detail than usual. Moreover, it is important to consider a debate where the disputants are actually trying to apply the models of population genetics to natural populations; only then can their proper interpretations become fully apparent. (Indeed, I contend that some of the philosophical confusion has arisen because authors have considered only the models themselves, and not the phenomena that the models are attempting to represent). A prime candidate for just such a case study is what Provine (1986) has termed " The Great Snail Debate, " that is, the debates over the highly polymorphic land snails Cepaea nemoralis and C. hortensis in the 1950s and early 1960s. These studies represent one of the best, if not the best, of the early attempts to demonstrate drift in natural populations. 3 Of course, some excellent historical accounts of the changes in the usages and meanings of random drift have been written already. Some of these histories of random drift have a broad scope this volume). I am very much indebted to these works. However, to my knowledge no one has written on the concepts of drift and selection in the debates over Cepaea with a focus on the views of the disputants themselves. This study reveals that much of the present-day confusion over the concepts of drift and selection is rooted in confusions of the past. Nonetheless, there are lessons that can be learned about nonadaptiveness, random sampling, and causality with respect to these two concepts. My approach will be to analyze the published works of the major disputants: These papers were chosen because they have become classics in the field. Moreover, Cain and Sheppard (1950) is the paper where the authors most thoroughly set out their selectionist arguments and their concerns with the previous studies of Cepaea. Lamotte (1959a) is the paper that attributes a …