The Come-Hither Voice

Forget the scent of a woman. Listen to her voice to find out if she's in the mood, researchers say.

Female animals produce a variety of cues to let males know they're fertile and looking to mate. For example, research on humans has shown that women's faces and scents become even more attractive to men as levels of a chemical called luteinizing hormone rise in women, and their ovarian follicles prepare to release an egg. Female lap dancers even appear to earn higher tips when ovulating (ScienceNOW, 5 October). In certain animals, such as cows and elephants, the females moo, bellow, and grunt more during ovulation. But no one had looked for a link between ovulation and women's voices.

Two researchers at the University of California, Los Angeles, decided to examine the question by comparing voice recordings of women at different stages of the menstrual cycle. They enlisted 69 women between the ages of 18 and 39 who were not on birth control, and they used urine tests to analyze the woman's level of luteinizing hormone. The volunteers were recorded saying vowel sounds "eh-ee-ii-o-oo" and a sentence, "Hi, I am a student at UCLA" at the peak of ovulation and at the end of the reproductive cycle, just before the women began menstruating.

The researchers then analyzed the two samples for differences in traits such as pitch, speech rate, and scratchiness, or sound quality. On average, the women's voices were about 5 hz higher in pitch at the peak of ovulation than before menstruation. That's a small difference, so the researchers also played the recordings to a group of 15 men and women to see if humans could detect the difference. The listeners could distinguish the higher one 55% of the time, slightly better than chance, the researchers report today in the Proceedings of the Royal Society B: Biology Letters.

The pitch difference occurred only when women uttered the sentence, not when they made the vowel sounds, the scientists note. Lead researcher Greg Bryant, an evolutionary psychologist, says this suggests the hormone surge doesn't alter the vocal chords; instead, it may play out on a more subliminal level. "It's motivating them to dress differently and walk differently," he says, citing previous research that showed women act in ways perceived as more feminine during ovulation. "It could be making them talk differently."

Ben Jones, a psychologist at the University of Aberdeen in the U.K. who has studied how changes in the reproductive cycle affect women's behavior, says the findings "fit nicely" with previous research on ovulation and female behavior. "The picture that's emerging is that all these factors work together to increase the likelihood of women having healthy kids," Jones says. That's because increasing one's femininity might prove more appealing to the most masculine--and thus healthiest--mates, he says.