Mental traits as fitness indicators. Expanding evolutionary psychology's adaptationism.

According to most evolutionary psychologists, human psychological adaptations can be recognized by criteria such as high efficiency, high complexity, high modularity, low phenotypic variance, low genotypic variance, low heritability, universality across cultures, and universality across individuals. These criteria are appropriate for adaptations that have been shaped through stabilizing selection for survival utility. However, they are often inappropriate for adaptations that have been shaped by sexual selection through mate choice as reliable signals of heritable fitness. If some psychological adaptations evolved as sexually selected fitness indicators of this type, we should expect them to violate many standard criteria used by evolutionary psychology to distinguish adaptations from non-adaptations. This paper addresses the problems raised by new developments in sexual selection theory and animal signaling theory for evolutionary psychology's adaptationism. It suggests that our adaptationist criteria must recognize two typical kinds of psychological adaptations: naturally selected survival mechanisms and sexually selected fitness indicators.