Human sexual selection: male voice and face shape Part 1

Human sexual selection is a complex system of interactions, even with our modern social constructs and laws in the mix nature still plays its role. Humans are highly sexual dimorphic primate with differing body form and behaviours for males and females. Here I wanted to look at what selection pressures determine male features, in particular the traits of male voice and face shape. I did not look at female features here, as some research suggests that female face shape and voices are only somewhat influents by sexual selection, and that selection acts mainly on males.

Male features are thought to be influence by two selection factors: male-male interaction, where males are in contest with each other, favouring traits for excluding other males; and female-male interactions, where females select males, favouring traits that females find attractive. In male-male interaction, a male fends off other males in two ways by actual threat or by potential threat – display of dominance.  Although, actual threats may be less important in our modern society with law preventing them, they would have been in an evolutionary context a key factor. A perceived threat, on the other hand, may still affect mate success, as it would exclude other males. Being able to exclude other males would give a greater chance of mate success. And so, being/showing dominance by your outward appearance, from a male-male perspective, can be advantageous.

Studies have shown that there is a relationship between masculine vocal and facial features, and dominance. If then dominance led to better success, natural selection would act on these two traits. There was found to be a correlation between males having a lower more masculine voice and the perception of dominance by other males. In a study, it was shown that men would alter the pitch of their voice in accordance with their perceived dominance. It was seen that, a man would lower his pitch when talking to a male he thinks to be weaker than himself, and raise the pitch if he thinks he is weaker.

 By a similar token, men with stronger jaw line are perceived as being more masculine and more dominant. A stronger jaw line is thought be dominant in both appearance and practicality. Unlike voice, having a strong jaw would help in an actual fight; strong jaws are less likely to be broken. It is also thought that, facial hair may have evolved to increase the apparent size of the jaw. This could explain why some studies had found that: a male’s face with a beard was rated more dominate than clean-shaven one. Therefore, it can be seen that male-male interactions are controlled by the traits that intimidate/exclude competitors by a show of dominance.

to be continued 

References

Puts, D.A., Jones, B.C. & DeBruine, L.M. 2012, "Sexual selection on human faces and voices", Journal of sex research, vol. 49, no. 2-3, pp. 227.
C.L Apicella, D.R Feinberg & F.W Marlowe 2007, "Voice pitch predicts reproductive success in male hunter-gatherers", Biology Letters, vol. 3, no. 6, pp. 682-684.
Boothroyd, L.G., Cross, C.P., Gray, A.W., Coombes, C. & Gregson-Curtis, K. 2011, "Perceiving the facial correlates of sociosexuality: Further evidence", Personality and Individual Differences, vol. 50, no. 3, pp. 422-425.