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Concepts of Drift and Selection in “The Great Snail Debate” of the 1950s and Early 1960s

Millstein, Roberta L. (2007) Concepts of Drift and Selection in “The Great Snail Debate” of the 1950s and Early 1960s. [Preprint]


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Recently, much philosophical discussion has centered on the best way to characterize the concepts of random drift and natural selection, and, in particular, on the question of whether selection and drift can be conceptually distinguished (Beatty 1984; Brandon 2005; Hodge 1983, 1987; Millstein 2002, 2005; Pfeifer 2005; Shanahan 1992; Stephens 2004). 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. A prime candidate for just such a case study is what William Provine (1986) has termed “The Great Snail Debate,” that is, the debate over the highly polymorphic land snails Cepaea nemoralis and Cepaea hortensis in the 1950s and early 1960s. This study will reveal 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, indiscriminate sampling, and causality with respect to these two concepts. In particular, this paper will shed light on the following questions: 1) What is “drift”? Is “drift” a purely mathematical construct, a physical process analogous to the indiscriminate sampling of balls from an urn, or the outcome of a sampling process? 2) What is “nonadaptiveness,” and is a proponent of drift committed to claims that organisms’ traits are nonadaptive? 3) Can disputes concerning selection and drift be settled by statistics alone, or is causal information essential? If causal information is essential, what does that say about the concepts of “drift” and “selection” themselves?

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Item Type: Preprint
Millstein, Roberta L.
Additional Information: Forthcoming in Joe Cain and Michael Ruse (eds.), Descended from Darwin: Insights into the History of Evolutionary Studies, 1900-1970.
Keywords: random drift, natural selection, Cepaea nemoralis, indiscriminate sampling, bottleneck, founder effect, Maxime Lamotte, Arthur J. Cain, Paul M. Sheppard, John D. Currey, adaptationist, selectionist, neutralist, relative significance debate, causation, statistical analysis
Subjects: Specific Sciences > Biology > Evolutionary Theory
Specific Sciences > Biology
General Issues > History of Science Case Studies
Depositing User: Dr. Roberta L. Millstein
Date Deposited: 03 Dec 2007
Last Modified: 07 Oct 2010 15:15
Item ID: 3695

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