A study of non-western and western women's body shapes found that the "perfect" hour-glass or pear shape supposedly favoured by men where the waist to hip ratio is 0.7 or less, is rarely found among women who have to rely on their own resources, such as going out to work or to search for food, to support themselves and their families. They have more cylidrical body shapes because of androgen hormones that not only cause the waist to carry more fat, but also help them become physically stronger, more resilient against stress and more competitive|: what many might regard as a highly beneficial trade-off.

These are the findings of a study by Elizabeth Cashdan, an anthropologist at the University of Utah in Salt Lake City, USA, whose findings are published in the December issue of Current Anthropology.

Having a body that isn't "perfect" in the conventional sense may have substantial benefits for women, concluded Cashdan. Hormones that make women physically stronger, more competitive, better able to withstand stress, also move fat from the hips to the waist. So societies where these traits are emphasized in women may also have fewer women with the classic hourglass figure.

Evidence from medical studies suggests that the more curvy female shape with a waist to hip ratio of 0.7 or less is closely linked to higher fertility and lower rates of chronic diseases. Research also suggests that when selecting a female mate, men tend to favour the 0.7 or lower waist to hip ratio, which makes sense to those studying evolutionary biology because a healthy fertile female mate increases the chances of the man's genes being passed onto a new generation.

But when she looked at women's waist to hip ratios in 33 non-Western and 4 European populations, Cashdan found that the average was above 0.8. This seemed to turn the evolutionary idea about the ideal being 0.7 and lower on its head, unless there was some other explanation that favoured a female waist to hip ratio of 0.8 and higher.

Cashdan suggested the answer lies in hormones, and androgens in particular. Androgens include testosterone, which in women increases the amount of body fat around the waist as opposed to the hips. This is the apparent downside which works against the evolutionary male-preference based theory. But the upside is that it brings with it important survival traits for the woman who has to rely on her own resources to support herself and her family, traits such as increased stamina and strength, and competitiveness. Another hormone is cortisol which increases waist fat but it also increases the body's resilience to stress.

Cashdan wrote that:

"The hormonal profile associated with high WHR (waist-to-hip ratio) … may favor success in resource competition, particularly under stressful circumstances."

"The androgenic effects -- stamina, initiative, risk-proneness, assertiveness, dominance -- should be particularly useful where a woman must depend on her own resources to support herself and her family," she explained.

So for women in many societies, trading a thin waist for increased resourcefulness is a good deal. And there is evidence that this affects male mate preferences in different societies too.

For example, in Greece, Portugal and Japan, where women are less economically independent, men show a higher preference for a thin waist than their counterparts in Britain and Denmark, where there is more equality among the sexes. And in some non-Western societies where food is scarce and women shoulder the responsibility for finding it, men actually prefer women with a higher waist to hip ratio.

In other words, trading the benefits of a thin waist for better ability to collect resources may be a good deal in certain societies and situations. And there is evidence that male mate preferences may reflect this trade-off, according to Cashdan.

Cashdan wrote that perhaps waist to hip ratio is a useful signal for men when choosing a mate, but the extent to which they go for a higher or lower ratio will depend on the "degree to which they want their mates to be strong, tough, economically successful and politically competitive."

Cashdan did not forget one very important point:

"And from a woman's perspective, men's preferences are not the only thing that matters," she added.

"Waist-to-Hip Ratio across Cultures: Trade-Offs between Androgen- and Estrogen-Dependent Traits."
Elizabeth Cashdan.
Current Anthropology Vol 49, No 6, December 2008.

Click here for Current Anthropology.

Sources: Chicago Journals.

Written by: Catharine Paddock, PhD