How (not) to bring psychology and biology together

Evolutionary psychologists often try to ‘‘bring together’’ biology and psychology by making predictions about what specific psychological mechanisms exist from theories about what patterns of behaviour would have been adaptive in the EEA for humans. This paper shows that one of the deepest methodological generalities in evolutionary biology—that proximate explanations and ultimate explanations stand in a many-to-many relation—entails that this inferential strategy is unsound. Ultimate explanations almost never entail the truth of any particular proximate hypothesis. But of course it does not follow that there are no other ways of ‘‘bringing together’’ biology and psychology. Accordingly, this paper explores one other strategy for doing just that, the pursuit of a very specific kind of consilience. However, I argue that inferences reflecting the pursuit of this kind of consilience with the best available theories in contemporary evolutionary biology indicate that psychologists should have a preference for explanations of adaptive behavior in humans that refer to learning and other similarly malleable psychological mechanisms—and not modules or instincts or any other kind of relatively innate and relatively non-malleable psychological mechanism.