An imperfect body might be just what the doctor ordered for women and key to their economic success, an anthropologist now says.
While pop culture seems to worship the hourglass figure for females, with a tiny waist, big breasts and curvy hips à la Marilyn Monroe, this may not be optimal, says anthropologist Elizabeth Cashdan of the University of Utah.
That's because the hormones that make women physically stronger, more competitive and better able to deal with stress also tend to redistribute fat from the hips to the waist.
So in societies and situations where women are under pressure to procure resources and otherwise bring home the bacon, they may be less likely to have the classic hourglass figure, Cashdan hypothesizes in the December issue of the journal Current Anthropology.
Until now, scientists (and apparently Western society) thought a curvy figure trumped other body shapes.
The idea was based on results from medical studies that suggested a curvy waist-to-hip ratio of 0.7 or lower (meaning the waist is significantly narrower than the hips) is associated with higher fertility and lower rates of chronic disease.
In addition, past research has revealed that men prefer a ratio of 0.7 or lower when looking for a mate.
The preference makes perfect sense, according to evolutionary psychologists, because the low ratio is a reliable signal of a healthy, fertile woman.
Along those lines, Playboy centerfolds tend to have a waist-to-hip ratio of 0.68, Cashdan found.
However, women around the world tend to have larger waist-to-hip ratios (more cylindrical than hourglass-shaped) than is considered optimal by these medical and social standards.
Specifically, Cashdan compiled data from 33 non-Western populations and four European populations, finding the average waist-to-hip ratio for women was above 0.8.
So if 0.7 is the magic number both in terms of health and male mate choice, Cashdan wondered why most women exhibit a significantly higher ratio.
That's where the hormones come in.
A little testosterone
Androgens, a class of hormones that includes testosterone, increase waist-to-hip ratios in women by increasing visceral fat, which is carried around the waist.
But on the upside, increased androgen levels are also associated with increased strength, stamina and competitiveness.
Cortisol, a hormone that helps the body deal with stressful situations, also increases fat carried around the waist.
Hormone levels linked with a high waist-to-hip ratio could lead to such health benefits, which would be particularly useful during times of stress, Cashdan said.
These benefits could outweigh those attained from having the tiny waist, hourglass figure, she said.
Perhaps the differences between predominant body shapes in some societies have to do with sexual equality, Cashdan said.
In Japan, Greece and Portugal, where women tend to be less economically independent, men place a higher value on a mate's thin waist than men in Britain or Denmark, where there tends to be more sexual equality, Cashdan said.
And in some non-Western societies where food is scarce and women bear the responsibility for finding it, men actually prefer larger waist-to-hip ratios.
"Waist-to-hip ratio may indeed be a useful signal to men, then, but whether men prefer a [waist-to-hip ratio] associated with lower or higher androgen/estrogen ratios (or value them equally) should depend on the degree to which they want their mates to be strong, tough, economically successful and politically competitive," Cashdan writes.
She added, "And from a woman's perspective, men's preferences are not the only thing that matters."
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