KEY POINTS:
A woman's voice becomes more attractive at the point in her monthly cycle when she is at her most fertile, a study of vocal changes during ovulation has found.
If the findings can be replicated, they will add further weight to the theory that women give off subtle
and unintentional cues about their fertility as part of an evolutionary battle centred on attractiveness and fidelity.
The research found that men tend to find higher-pitched female voices more attractive, so the idea is that a woman would sound less like Mariella Frostrup and more like Marilyn Monroe at a certain time of the month.
Unlike most mammals, human females show no obvious signs of oestrus. But some scientists believe there may be hidden signals that men and other women subconsciously identify.
Nathan Pipitone and Gordon Gallup, of the State University of New York in Albany, investigated vocal attractiveness by recording female volunteers counting from one to 10 at four different points in their menstrual cycle, which they categorised as low to high risk of conception.
They then asked a panel of men and women to listen to the recorded voices and give their unbiased assessment as to whether they sounded attractive.
Both sexes judged the women's voices to be sexiest when they were recorded at the times during their menstrual cycle when they were at their most fertile.
"The results showed a significant increase in voice attractiveness ratings as the risk of conception increased across the menstrual cycle," the scientists' report said.
"More work is needed to identify the biological mechanisms that underlie these perceptual differences, but growing evidence points to the impact of hormones on the larynx as being the source of these changes.
The study is to be published in the Journal of Evolution and Human Behaviour.
A separate study at the University of California in Los Angeles investigated the pitch of 33 women's voices at various points in the menstrual cycle. They found that the women tended to become higher pitched at their most fertile point.
Previous work on female voice pitch had established that men tend to find higher-pitched voices more attractive. Taken together, the findings of all three studies suggest that the female voice increases in pitch at their most fertile moment.
The fact that men notice differences in vocal attractiveness suggests there is a subtle evolutionary battle of the sexes going on, Dr Gallup said.
As women evolved ever more efficient ways to conceal fertility, men become more sensitive to small and subtle changes.
Geoffrey Millar, of the University of New Mexico, has shown that lap dancers tend to be given bigger tips by male customers when the women are ovulating.
"The voice changes might explain some of the shift in lap dancer tip earnings. Dancers certainly chat with their customers," Dr Millar said.
- INDEPENDENT