On the explanatory roles of natural selection

Can selection explain why individuals have the traits they do? This question has generated significant controversy. I will argue that the debate encompasses two separable aspects, to detrimental effect: (1) the role of selection in explaining the origin and evolution of biological traits and (2) the implications this may have for explaining why individuals have the traits they do. (1) can be settled on the basis of evolutionary theory while (2) requires additional, extra-scientific assumptions. By making a distinction between traits affected by a single factor and traits affected by multiple factors I show that selection can, under certain conditions, help explain the origin of traits. Resolving the first aspect enables us to critically assess the various incompatible and independent philosophical commitments made within the second aspect of the debate.