Ladies, which do you find more alluring: the soaring high notes of British crooner Sam Smith, or the deep, soulful tones of Barry White?

The boyish squeak of actor Michael Cera, or the rich bass of James Earl Jones?

A new study finds that it may not matter so much what women think, at least biologically speaking. Deep voices are more about men showing each other who is boss.

The research, whose authors included eight scholars from Pennsylvania State University, marks the latest attempt by science to answer that age-old question of how humans pick their mates.

In addition to asking hundreds of men and women to rate the attractiveness and perceived dominance of recorded human voices, the researchers also undertook a vast review of the animal kingdom. Upon studying 1,721 grunts, cries, and other vocalizations culled from two dozen species of primates, they found a surprise:

The average difference in pitch between male and female voices was greater in humans than in most of the other primates. And humans exhibited the largest such difference among any of the half-dozen primates classified as apes.

But why?

"Is it that low-pitched males are winning mating opportunities because females find them attractive, or is it because they are intimidating other males?" asked study coauthor Alex Hill, a former Penn State graduate student now teaching at the University of Washington. "That's the crux of the issue."

To answer that question, the researchers enlisted 558 women and 568 men, all Penn State students who described themselves as heterosexual, to evaluate hundreds of recordings of male and female voices.

Each female voice was rated by 15 men for attractiveness on a seven-point scale; each male voice was rated by 15 men for its perceived dominance, and by 15 women for attractiveness.

Women rated deeper male voices as sounding more attractive, generally, and men rated deeper voices in their fellow men as seeming more dominant - but the impact of pitch on perceived dominance was much stronger, statistically speaking. (The frequency of women's voices did not predict whether men found them attractive, however.)

The study provides valuable insight into human reproductive choices, said Carolyn Hodges-Simeon, a Boston University assistant professor of anthropology who was not involved with the study.

Still not entirely clear is why the pitch of a man's voice would matter in competitive situations, as the depth of a voice does not correspond strongly with body mass.

"Why would anyone care about the voice?" Hodges-Simeon said. "It's not like muscle. Muscle is something that could actually harm you."

The new study, whose lead author was Penn State associate professor of anthropology David A. Puts, provided some clues on that score as well.

The researchers collected saliva of Penn State students and measured their levels of testosterone and cortisol, a stress hormone. They found that men with higher testosterone levels and lower levels of cortisol generally had deeper voices.

That hormonal signature has previously been associated with healthy immune function. So to some degree, deep voices seem to serve as a kind of evolutionary marker for good health.

In modern times, advances in health care have leveled the playing field somewhat. But eons ago, good health meant the ability to pass on genes.

"A lot of what we find attractive in prospective mates, we think, has to do with our evolutionary past," Hill said. "We were essentially walking health records."

The findings were published in the British journal Proceedings of the Royal Society B.

tavril@phillynews.com

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