Biological and cultural influences on the expression of sex differences: Commentary on Costello et al. (2026).

As nicely explained by Costello et al. (2026), evolution provides a powerful metatheory for more fully understanding many traits and phenomena that are of interest to psychologists. I add to their thoughtful discussion by elaborating on how Darwin's sexual selection-competition for mates and discriminating mate choices-provides a heuristic for understanding sex differences and can be used to generate predictions about how the magnitude of these differences can vary across time and place. The basic prediction is that reductions in disease burden, nutritional deficits, and intense social conflict and gains in personal freedom will result in an increase in the magnitude of many sex differences. (PsycInfo Database Record (c) 2026 APA, all rights reserved).