Abstract

In recent years, philosophers of science have found a renewed interest in mechanisms. The motivation is the thought that the elucidation of a mechanism generates a causal explanation for the phenomenon under investigation. For example, a question such as, How do rats form spatial memories of their environments?, is answered by elucidating the regular causal mechanisms responsible for the individual development of spatial memory in rats. But consider a slightly different question: How do some rats come to have better spatial memory than other rats? This is a question about the causes of variation responsible for variation in spatial memory. The first question demands an answer about regularity; the second question demands an answer about variation. The account of causal-mechanical explanation on offer by philosophers of science captures regularity, but it neglects variation. In this essay, I attempt to modify the mechanical program so as to incorporate both regularity and variation. The task is to explicate the relationship between the regular causal mechanisms responsible for individual development and the causes of variation responsible for variation in populations. As it turns out, this is precisely the relationship that has divided the biometric research tradition and the developmental research tradition in the long-standing debates over genotype-environment interaction, or G×E. Ultimately, the product will be an account of causal-mechanical explanation that captures both regularity and variation, and which may be utilized to resolve an aspect of the debates over G×E.