Competition between men drove evolution of deep voices
Deep, booming male voices among primates, including humans, may have evolved more to intimidate rivals than to attract females, a multinational team of researchers says.
In a paper published in the Proceedings of the Royal Academy Sciences B, the team said deep voices were more likely when primate species were polygynous (a male having many partners), not monogamous, and thus males were competing more intensely for mates.
The team said that as males evolved to become more monogamous, there was less difference between male and female voices.
"If you look at what men's traits are designed for, they look much better designed for intimidating other males than for attracting females," said lead researcher Dr David Puts of Pennsylvania State University.
The study had three parts, looking at the links between voice pitch and mating, the influence of pitch on attractiveness for both males and females, and the link between deeper voices and being perceived by other males as being dominant.
Voice pitch was measured by the "fundamental frequency" between males and females, the lowest pitch that vocalisations reach.
Analysis of 1,721 recordings of vocalisations from humans, other apes, and monkeys from the Americas and Asia showed a much greater difference between males and females in species where males mate with more than one female than where pairs mate exclusively.
The researchers suggest a male with a lower pitched voice could have the edge in securing mates because it is seen by rivals to be intimidating.
Humans show greatest difference in fundamental pitch
However, humans had the greatest difference in pitch between the sexes of all the ape species, despite anthropologists regarding humans as most often monogamous and, despite a larger body size, being associated with less difference between the sexes.
Dr Puts, however, said humans were effectively moderately polygynous, even in monogamous societies.
"Men are more likely to marry again after divorce, are likely to marry a younger wife and more likely than women to reproduce again with their new spouse," he said.
The second part of the study had 15 men and 15 heterosexual women rating the attractiveness of 258 women and 175 men reading the same piece of text.
Men also rated each male voice on "dominance".
The pitch of female voices did not affect ratings of attractiveness, but deeper male voices were rated as more dominant by men and more attractive by women.
The link between pitch and dominance was three times stronger than that between pitch and attractiveness, leading researchers to suggest that deeper voices evolved more by competition between males than by female choice.
Voices may allow males to establish a hierarchy without having to resort to violence, the researchers suggested.
The third part of the study found a connection between deep voices and health, with a lower pitch connected with lower levels of the stress hormone cortisol, higher levels of testosterone, and a healthy immune system, suggesting that deeper male voices are perceived as more attractive because they indicate a healthy mate.
"Our data supported the sexual selection hypothesis," the researchers wrote.
"Our data also indicate that sex differences result mainly from selection on males rather than females."