Abstract
Humans are sexually dimorphic: men and women differ in body build and composition, craniofacial structure, and voice pitch, likely mediated in part by developmental testosterone. Sexual selection hypotheses posit that, ancestrally, more 'masculine' men may have acquired more mates and/or sired more viable offspring. Thus far, however, evidence for either association is unclear. Here, we meta-analyze the relationships between six masculine traits and mating/reproductive outcomes (96 studies, 474 effects, N = 177,044). Voice pitch, height, and testosterone all predicted mating; however, strength/muscularity was the strongest and only consistent predictor of both mating and reproduction. Facial masculinity and digit ratios did not significantly predict either. There was no clear evidence for any effects of masculinity on offspring viability. Our findings support arguments that strength/muscularity may be sexually selected in humans, but cast doubt regarding selection for other forms of masculinity and highlight the need to increase tests of evolutionary hypotheses outside of industrialized populations.
Highlights
Sexual dimorphism refers to sex differences in morphological and behavioral traits, excluding reproductive organs [1], with particular emphasis on traits thought to have evolved through sexual selection [2]
While we find that the effect of facial masculinity on mating was similar in size to that of other traits (r = .08), it was not significantly different from zero, suggesting more variability in effects
We found that voice pitch, height, and testosterone levels were associated with mating success in mostly low fertility populations, but not with actual reproductive fitness in high fertility populations
Summary
Sexual dimorphism refers to sex differences in morphological and behavioral traits, excluding reproductive organs [1], with particular emphasis on traits thought to have evolved through sexual selection [2]. 8% taller than women [6] and weigh approximately 15% more [7] Relative to this fairly modest body size dimorphism, upper body musculature and strength are highly dimorphic in humans: compared to women, men have 61% more overall muscle mass, and 90% greater upper body strength [8]. Fundamental frequency, commonly referred to as voice pitch, is nearly six standard deviations lower in men than in women [15]. The development of these masculine traits in men is influenced by exposure to androgens, testosterone. With the exception of 2D:4D, which is commonly claimed to be influenced primarily by prenatal testosterone levels and is present at birth (16; but see 17), masculine traits generally develop or become exaggerated following a surge in testosterone production at sexual maturity [18-20] – it is not necessarily clear whether the size of that surge corresponds directly to the extent of trait expression
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