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Think of it as the Barry White factor: a deep voice, like the rumble of midnight thunder in July. Women love it; men try to imitate it, or failing that, put in a CD and dim the lights to create the right mood.
It wasn't just lyrics that earned Barry his nickname, the Sultan of Smooth Soul. He had talent. He had rhythm. He had... thicker vocal cords.
The physical differences between men's and women's vocal cords are like those between a cello and violin, explains David Puts, assistant professor of biological anthropology at Penn State's University Park campus. Compared to a violin, the cello's much longer, thicker strings vibrate more slowly to produce a low frequency, and the instrument's larger interior space produces more resonant sound, which we perceive as "deep." In humans, these physical differences don't emerge until puberty, when a rise in testosterone causes a boy's vocal cords to grow longer and thicker. His voice can drop as much as an octave.
Puts first began to explore the evolution of deep voices in males when looking for a dissertation topic as a graduate student. At the time, research on the role of voice in sexual selection was sparse, and he felt that focusing on such an understudied phenomenon might help to open up a new research field. Since then, his research has revealed that women are indeed attracted to deeper voices, particularly when in the fertile part of their menstrual cycle.
"This effect is most pronounced for women's sexual preferences, rather than their preferences for partners in long-term, committed relationships," Puts clarifies. "Many researchers have concluded that masculine traits, including a deep voice, reflect men's genetic quality. After all, if a woman can obtain good genes for her offspring from a potential mate, it would make sense to be more sexually attracted to men with the best genes when fertile."
"However," he says, "evidence suggests men evolved deeper voices mainly for intimidating other men rather than attracting women." Studies show that men with deeper voices tend to have higher testosterone levels (an indicator of dominance) and a more athletic body type.
If you're a man angling to convince your boss you deserve a promotion or to win the heart of your dream girl, should you lower your voice when you talk to them? It depends. Puts' work has shown that manipulating "vocal masculinity"—the deepness of one's voice—has a much bigger effect on perceptions of dominance than it does on perceptions of attractiveness. So while dropping your vocal tones may give your boss an unconscious impression that you're leadership material, it probably won't make you seem much more attractive to a potential date—unless you have a feminine voice to begin with, clarifies Puts.
So what about women with deep voices? Despite the popularity of baritone beauties like crooner Billie Holiday and actress Kathleen Turner, men tend to prefer higher voices in women, says Puts. This is something he and colleagues are currently exploring, but he suspects a higher voice indicates youth and fertility.
Despite being involved with voice research for nearly a decade, Puts only recently learned his own voice frequency while testing recording equipment. His voice registered around 99 Hertz (Hz), "a little lower than average," he says.
David A. Puts, Ph.D., assistant professor of biological anthropology, recently published The Evolution of Human Sexuality: An Anthropological Perspective. He can be reached at dap27@psu.edu.