Female driven reduction of sexual dimorphism in hominins

This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint. You must log in to post a comment. There are no comments or no comments have been made public for this article. This is a Preprint and has not been peer reviewed. This is version 1 of this Preprint. Add a Comment You must log in to post a comment. Comments There are no comments or no comments have been made public for this article. Sexual dimorphism is a key indicator of social structure and selective pressures in primate evolution, yet its evolutionary drivers in hominins remain contentious. Here, we combine cutting edge dimorphism estimation methods, with Bayesian phylogenetic comparative analyses to disentangle the sex-specific contributions and evolutionary dynamics underlying changes in body mass and canine size across over 300 hominin specimens. Our results reveal a consistent reduction in body mass dimorphism over time, driven not by male body size reduction - as is predicted by prevalent hypotheses - but by a significant increase in female body mass. These finding challenges prevailing assumptions about the weakening of sexual selection on males and instead supports a model of positive selection on female size, likely linked to reproductive and ecological demands. In contrast, canine size dimorphism is minimal throughout hominin evolution, with evidence of coordinated size reduction in both sexes, consistent with decreased reliance on canine-based competition. These patterns underscore divergent selective trajectories for different sexually dimorphic traits and highlight female-driven morphological evolution as a dominant force in hominin body size diversification. Our study provides a new framework for interpreting dimorphism in the fossil record and offers fresh insight into the evolutionary mechanisms shaping human ancestry. https://doi.org/10.32942/X2S05N Ecology and Evolutionary Biology, Evolution, Life Sciences human evolution, sexual selection, social behaviour Published: 2025-06-21 05:17 Last Updated: 2025-06-21 05:17 CC-By Attribution-NonCommercial-NoDerivatives 4.0 International Data and Code Availability Statement: Data will be made publicly available upon publication of the article in a peer-reviewed journal. Language: English