The Economist (May 6) has a most interesting article on female body shape and fertility: it seems that girls with small waists and big boobs are three times more likely to get pregnant at any given time than slender babes.
The reason: busty babes have much higher levels of the hormones progesterone and 17-b-estrodiol, whose concentrations are directly proportional to a woman’s fertility.
Here’s the article:
Gentlemen may or may not prefer blondes.
But, in rich countries at least, they do seem to prefer women with hour-glass figures. There have been various ideas about why this is so. The politically correct suggest that it is mere fashion – and point to evidence that tastes are sometimes different in poorer societies.
Those of a more biologically deterministic frame of mind suggest that wide hips, relative to waist size, are good for child bearing, and that large breasts deliver more milk.
What has not been widely suggested is that women with classic figures are simply more fertile.
But that is what Grazyna Jasienska and her colleagues at Harvard University hypothesize in the latest edition of the Proceedings of the Royal Society.
They have found that in women of child-bearing age, the levels of two hormones known to be associated with fertility are, as it were, geometry – dependent.
Dr. Jasienska measured the vital statistics of 119 women aged between 24 and 37.
She also took saliva samples from them over a whole menstrual cycle.
She then divided her sample into four categories – a combination of narrow or broad waist-to-hip ratio with small or large breast-size – and looked for statistically significant differences between them in the levels of progesterone and 17-b-estrodiol, two hormones whose concentrations are known to be related to a woman’s fertility.
The research by Dr. Jasienska and colleagues is published in the Proceedings of the Royal Society.
In the case of progesterone, both groups of narrow-waisted women had high hormone levels.
In that of 17-b-estrodiol, those with narrow waists and large breasts had elevated levels – and that level was particularly high at the time of ovulation.
Indeed, it was so high that Dr. Jasienska estimates such women are three times as likely as the others to become pregnant on any given occasion. In evolutionary terms that makes them very desirable mates indeed.
Why a woman’s shape should reflect her hormone levels is not yet clear.
That is one obvious next question to investigate. Another might be to put the boot on the other foot, and ask whether men with beer guts are less potent than their hunkier fellows.