A deep, low pitch voice is often sought after in a man, but a new study suggests this characteristic might have evolved to intimidate other males, not attract females.
The team at Pennsylvania State University studied Old and New World monkeys, as well as primates like humans and other apes. Namely, the researchers investigated how the fundamental frequency between males and females of each species varied on a case by case basis. The voiced speech of a typical adult human male will have a fundamental frequency from 85 to 180 Hz, and that of a typical adult female from 165 to 255 Hz.
After studying 1721 recordings, the biggest difference in fundamental frequency or pitch was found among polygynous primates. Because males mate with more than one female in polygynous species, the researchers reckon the lower-pitched voice can be seen as a tool to intimidate other males among which there must be fierce competition.
Among apes, at least, humans had the greatest variation in pitch between the sexes. It might be a stretch, but it seems like the signature lower timbre evolved to intimidate other males rather than woo females.
“If you look at what men’s traits look like they are designed for, they look much better designed for intimidating other males than for attracting females,” said David Puts of Pennsylvania State University, who led the study.
“Even in societies that only have monogamous marriage, 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,” said Puts. “So what you get is a mating system that is effectively moderately polygynous even in monogamous societies.”
In a second experiment, 285 women and 175 men were asked to read out loud a text. Each female voice, recorded beforehand, was rated for attractiveness by 15 men on a seven-point scale. The men had to rate the woman's voice with a view for both short and long term relationships. Similarly, each male voice was rated by 15 women. Then, each male recording was listened and rated for "dominance" by 15 men.
How deep was the voice of women mattered very little to the preferences of male listeners. However, deeper male voices were rated as more dominant by other males and more attractive by women. Moreover, the link between a deep voice and male dominance was three times stronger than the link to attractiveness for women.
“It’s not to say that our male ancestors were unabatedly at one another’s throats - lots of physical competition across a variety of species takes the form of threats and advertisement of dominance,” said Puts.
In a third experiment, the researchers found that those men with the lowest levels of the stress hormone cortisol and higher levels of testosterone had the deepest voices.
“Men who have higher testosterone and lower cortisol have a stronger immune response,” said Puts. “It may indicate their possession of a healthy immune system which would provide genes for producing a healthy immune system to their offspring,” he said.
“In humans it is likely both men and women have a choice in selection of their mate,” said David Perrett, professor of psychology at the University of St Andrews. “Some of the explanation for the difference between men and women’s voice pitch might come from the selection by males of women with relatively high pitched voices rather than all of the selection being down to men fighting men and women choosing the victors.”