Beatty on Chance and Natural Selection

In his (1984) John Beatty correctly identifies the issue of the role of chance in evolution as one of the liveliest disputes in evolutionary biology. He argues, on the basis of a carefully articulated example, that "Even on a proper construal of 'natural selection', it is difficult to distinguish between the 'improbable results of natural selection' and evolution by random drift". His other remarks indicate that he is thinking of conceptual as well as practical indistinguishability. In this discussion I take issue with one of the consequences Beatty draws from his example. I argue that the example at most shows that the effects of drift and selection are sometimes difficult to separate in practice, but that the stronger conceptual claim is not warranted. The deeper problems raised by the example are seen to demand causal, rather than conceptual, analysis.