Abstract
Humans are sexually dimorphic: on average men significantly differ from women in body build and composition, craniofacial structure, and voice pitch, likely mediated in part by developmental testosterone exposure. Hypotheses which attempt to explain the evolution of dimorphism in humans assume that more masculine men have historically achieved greater biological fitness. This may be because: more masculine men out-compete other men for mates; women preferentially select masculine men (e.g. due to their greater competitiveness and/or heritable immunocompetence); masculine men expend more energy on mating effort; and/or masculine men father more viable offspring. Thus far, however, evidence for an association between masculinity and mating/reproductive outcomes is unclear. We conducted the most comprehensive meta-analysis to date on the relationship between six types of masculine traits and mating/reproductive outcomes, comprising 474 effect sizes from 96 studies (total N = 177,044). Body masculinity, i.e. strength/muscularity, was the strongest and only consistent predictor of both mating and reproduction. Voice pitch, height, digit ratios, and testosterone levels all predicted mating; height and digit ratios also predicted some reproductive measures in some samples. Facial masculinity did not significantly predict either mating or reproduction. There was insufficient evidence for any effects on offspring mortality. Our findings support arguments that strength/muscularity can be considered sexually selected in humans, but raise concerns over other forms of masculinity. We are also constrained by lack of reproductive data, particularly from naturally fertile populations. Our data thus highlight the need to increase tests of evolutionary hypotheses outside of industrialized populations.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
More papers have been included in this version of the paper; all analyses and sample sizes have therefore been updated. Reproductive outcomes now include both fertility and reproductive success measures (the previous version only included fertility) and, in addition to analysing fertility and reproductive success together, we also analyse them separately. We have also added offspring mortality as a separate outcome measure. The overall pattern of results has not changed since the previous version.