Does male dimorphism matter?

A new analysis examines whether masculine traits impact reproductive success and number of sexual partners in men.
Digest
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A muscled man looking at his arms. Image credit: Public domain

Many species show sexual dimorphism: traits that are different or more exaggerated in either females or males. These traits are often thought to have evolved because they increase an individual’s chances of producing offspring. While the evolution of male dimorphism – often referred to as masculinity – is generally well understood in many animal species, opinions differ as to whether such traits also increase male reproduction in humans.

Lidborg et al. tried to shed light on the evolution of masculine traits in human males (such as a more robust-looking facial structure, and increased strength and muscularity) by testing whether men with these traits reported having more sexual partners and/or whether they had more children compared to men in which these traits were not as extreme. To do so, Lidborg et al. compiled previously published data from populations all across the world and tested the associations between the traits and both partner numbers and reproduction.

The results showed that men who were physically stronger and more muscular reported having more sexual partners and, in societies that do not use contraception, these men also had more children than other men. Lidborg et al. also found that in industrialized societies, men who were taller, had a lower voice pitch and higher testosterone levels also reported more sexual partners, but they did not produce more offspring. Lastly, the analysis showed that men with more robust facial structures faces did not report having more partners or more children.

These findings suggest that traits such as strength and muscle mass in men may be favoured by evolution. Importantly, this seems to be the case across all societies from which Lidborg et al. analyzed data. The results also show that some of the traits Lidborg et al. tested – such as being tall – might increase the number of partners men in industrialized countries have, but not the number of children men in more traditional societies (such as hunter-gatherers) produce. This could be because women’s preferences for men’s traits differ between cultures.

Ultimately, Lidborg et al.’s analysis suggests that across different cultural contexts, only strength and muscularity truly do seem to matter for men’s mating and reproduction.