The Scientific Fundamentalist

A look at the hard truths about human nature.

Barbie: Manufactured by Mattel, designed by evolution IV

Why are 36-24-36 the ideal female measurements?

Small waists

What are the ideal female measurements?  36-24-36.  Why are they considered to be the ideal female measurements?  It turns out that these numbers are not chosen arbitrarily.  There is precise evolutionary logic behind them.

An evolutionary psychologist at the University of Texas, Devendra Singh, has conducted experiments in different societies to demonstrate that men have a universal preference for low waist-to-hip ratios (the waist measurement divided by the hip measurement).  Presented with figure drawings of women identical in every way except the waist-to-hip ratio (varying from .7 to 1.0), most men in Singh’s experiments express preference for women with the waist-to-hip ratio of .7, which is very close to the waist-to-hip ratio of anyone with the 36-24-36 measurement (.67).

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I have personally and informally replicated Singh’s experiments in three different countries on three different continents (the US, New Zealand, and the UK), and found the same results as Singh.  The outcomes are remarkably uniform in every experiment in every country; most men prefer women with a .7 waist-to-hip ratio, and most women prefer men with a .9 waist-to-hip ratio.

Why, then, do men want women with low waist-to-hip ratios?  Singh argues that this is because healthy women have lower waist-to-hip ratios than unhealthy women.  A host of diseases -- such as diabetes, hypertension, heart attack, stroke, and gallbladder disorders -- change the distribution of body fat so that sickly women cannot maintain low waist-to-hip ratios.  Women with low waist-to-hip ratios are also more fertile; they have an easier time conceiving a child and do so at earlier ages because they have larger amounts of essential reproductive hormones.  And, of course, women who are already pregnant with another man’s child cannot maintain a low waist-to-hip ratio.

A woman’s waist-to-hip ratio also fluctuates, albeit very slightly, over the menstrual cycle; it becomes lowest during ovulation, when the woman is fertile.  Thus, men are unconsciously seeking healthier and more fertile women when they seek women with small waists.

The preference for a low waist-to-hip ratio, identified by Singh, explains both the popularity of corsets in many Western societies throughout history as a device to make women’s waists appear as small as possible, and the current trend of young women to bare their midriffs.  It also explains why it is teenage girls, not menopausal women, who are more likely to bare their midriffs as an honest signal of their high fecundity (the ability to conceive), just as it is young women, not old women, who grow their hair long as an honest signal of their health.  Once again, the superstardom of Britney Spears and Christina Aguilera is not the cause of young girls’ desire to show their midriffs; rather, it is the consequence of it.

The significance of waist-to-hip ratio in inferring women’s fecundity explains the importance of the second and the third numbers in the ideal female measurements of 36-24-36.  But what about the first 36?  What is it important for women to have 36-inch breasts?  That’s the topic of my next post.

Satoshi Kanazawa is an evolutionary psychologist at LSE and the coauthor (with the late Alan S. Miller) of Why Beautiful People Have More Daughters.

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