Large-breasted, narrow-waisted women have the highest reproductive potential, according to a new study, suggesting western men's penchant for women with an hourglass shape may have some biological justification.

Women with a relatively low waist-to-hip ratio and large breasts had about 30 per cent higher levels of the female reproductive hormone estradiol than women with other combinations of body shapes, found Grazyna Jasienska, at Jagiellonian University in Krakow, Poland and colleagues.

Two of the team, Peter Ellison and Susan Lipson at Harvard University in the US, have previously shown that higher levels of estradiol are indeed related to higher fertility in women trying to get pregnant.

"If there are 30 per cent higher levels, it means they are roughly three times more likely to get pregnant," Jasienska, a human biologist, told New Scientist.

"In Western societies, the cultural icon of Barbie as a symbol of female beauty seems to have some biological grounding," concludes the team. "I would be the last person to propagate Barbie," Jasienska notes wryly. "But when you think about the hourglass shape, Barbie is sort of the symbol."

Universal feature

The team studied 119 Polish women aged between 24 and 37, who were not taking any kind of hormonal contraception or medication. Women who were extremely underweight or overweight were not included.

Saliva samples taken from the women revealed that those with narrow waists and large breasts had on average 26 per cent higher levels of the hormone 17-b-estradiol, than women of other shapes. In the middle of their menstrual cycle, this peaked at 37 per cent higher levels than women in other groups.

Waist-to-hip ratio also had a strong effect on levels of another female hormone, progesterone. Jasienska, says that higher progesterone levels should also theoretically translate to increased fertility. However, large breast size was not significantly related to increased progesterone.

Jasienska says that a preference for low waist-to-hip ratios is a "universal feature" in psychological studies of men. "It was interesting to see what we observed in psychological studies has some biological background," she says.

Androgenous models

"The results are extremely intriguing," says Maryanne Fisher, a psychologist at York University in Toronto, Canada, whose study of Playboy centrefolds over 50 years revealed a drift in Western men's tastes.

She points out an ongoing debate over the relative importance of waist-to-hip ratio and body mass index (BMI) as features used by men to judge female attractiveness. She says women who have a "great" waist-to-hip ratio may not necessarily be attractive if they also have a high BMI.

Fisher's study of Playboy centerfolds showed that over 50 years men's preferences had moved from voluptuous to more androgenous models who had higher WHR but were thinner.

Jasienska notes that some non-Western societies do not use the same measurements of female attractiveness. In cultures which value large women, size may be a more important indicator of nutrition and health and therefore fertility, she says.

Journal reference: Proceedings of the Royal Society B(DOI: 10.1098/rspb.2004.2712)

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