 The capacity for natural selection to explain has come under fire from several directions. An important challenge to the explanatory power of selection was made by Gould and Lewontin who impugn the veracity of selectionist accounts of the origin of traits whose correctness is pinned on nothing more than their plausibility and capacity to explain (Gould &amp; Lewontin 1979: 588). Gould and Lewontin offer several examples of traits for which such “just so” stories are easy to construct but nonetheless taken to be true on the basis of little or no evidence beyond the plausibility of the accounts and their consistency with the theory. Lennox argues that, when not taken as even purportedly true, “just so stories” can play a genuine, if modest, role in the evaluation of scientific theories as thought experiments used to assess the explanatory potential of the theory (see also Mayr 1983; Lennox 1991; entry on  adaptationism).  In the debate over Darwin’s theory, thought experiments of this sort were deployed by both Darwin and his critics in ways both legitimate and rhetorically effective (Lennox 1991).