An Updated Theoretical Framework for Human Sexual Selection: from Ecology, Genetics, and Life History to Extended Phenotypes

Abstract

Sexual selection typically centers on bodily and psychological traits. Non-bodily traits ranging from housing and vehicles through art to social media can, however, influence sexual selection even in absence of the phenotype proper. The theoretical framework of human sexual selection is updated in this article by unifying four theoretical approaches and conceptualizing non-bodily traits as extended phenotypic traits. Existing research is synthesized with extended phenotype theory, life history theory, and behavioral ecology. To test population-level hypotheses arising from the review, ecological and demographic data on 122 countries are analyzed with multiple linear regression modelling. A four-factor model of intelligence, adolescent fertility, population density, and atmospheric cold demands predicts 64% of global variation in economic complexity in 1995 and 72% of the variation in 2016. The evolutionary pathways of extended phenotypes frequently undergo a categorical broadening from providing functional benefits to carrying signalling value. Extended phenotypes require investments in skills and bioenergetic resources, but they can improve survival in high latitudes, facilitate the extraction of resources from the environment, and substantially influence sexual selection outcomes. Bioenergetic investments in extended phenotypes create individual- and population-level tradeoffs with competing life history processes, exemplified here as a global tradeoff between adolescent fertility and economic complexity. The merits of the present model include a more systematic classification of sexual traits, a clearer articulation of their evolutionary-developmental hierarchy, and an analysis of ecological, genetic, and psychological mechanisms that modulate the flow of energy into extended phenotypes and cultural innovations.