Why Beautiful People Have More Daughters: From Dating, Shopping, and Praying to Going to War and Becoming a Billionaire–Two Evolutionary Psychologists Explain Why We Do What We Do (8 page)

Small Waist

Why are 36–24–36 considered the ideal female measurements? It turns out that these numbers are not chosen arbitrarily.

An evolutionary psychologist at the University of Texas, Devendra Singh, conducted experiments in different societies to demonstrate that men have a universal preference for low waist-to-hip ratio (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 0.7 to 1.0), most men in Singh's experiments expressed preference for women with the waist-to-hip ratio of 0.7, which is very close to the waist-to-hip ratio of anyone with the 36–24–36 measurements (0.67).
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One of us (Kanazawa) has 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. Most men prefer women with a 0.7 waist-to-hip ratio, and most women prefer men with a 0.9 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.
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And, of course, women who are already pregnant with another man's child cannot maintain a low waist-to-hip ratio.

The female waist-to-hip ratio also fluctuates, albeit very slightly, over the menstrual cycle; it becomes lowest during ovulation, when the woman is fertile.
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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 like 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 was not the
cause
of young girls' desire to show their midriffs; rather, it is a consequence of it.

Large Breasts

Why men prefer women with large breasts had long been a mystery in evolutionary psychology, especially since the size of a woman's breasts has no relationship with her ability to lactate; women with small breasts can produce as much milk for their infants as those with large breasts.
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So women with large breasts do not necessarily make better mothers than women with small breasts. Why, then, do men prefer women with large breasts? There was no satisfactory answer to this question until recently.

The then Harvard anthropologist Frank Marlowe suggested a solution to this puzzle in the late 1990s,
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although with hindsight it is another mystery why nobody else thought of the idea sooner. Marlowe makes the simple observation that larger, and hence heavier, breasts
sag
more conspicuously with age than do smaller breasts. Thus, it is much easier for men to judge a woman's age (and her reproductive value) by sight if she has larger breasts than if she has smaller breasts, which do not change as much with age. Recall that there were no driver's licenses or birth certificates that men could check to learn how old women were in the ancestral environment. There was no calendar and thus no concept of birthdays in the ancestral environment, so women themselves didn't know exactly how old they were. The ancestral men needed to infer a woman's age and reproductive value from some physical signs, and the state of her breasts provided a pretty good clue, but only if they were large enough to change their shape conspicuously with age. Men could tell women's ages more accurately, and attempt to mate with only young women, if they had larger breasts. Marlowe hypothesizes that this is why men find women with large breasts more attractive.

More recently, there has been a competing evolutionary psychological explanation for why men prefer women with large breasts. A study of Polish women shows that women who simultaneously have large breasts and a tight waist have the greatest fecundity, indicated by their levels of two reproductive hormones (17-ß-estradiol and progesterone).
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So men may prefer women with large breasts for the same reason as they prefer women with small waists. Further empirical evidence is necessary to evaluate which of these two competing evolutionary psychological explanations is more accurate. This is just one of many areas where there are competing hypotheses in evolutionary psychology—a sign of active, healthy science.

Men can accurately infer a woman's age and reproductive value if they can directly observe their breasts and other physical features (such as the fat content of the body). But what would men do if they could not directly observe women's bodies? What if the woman's body is concealed, by heavy clothing, for instance? Men need another way to determine a woman's age: her hair color.

Blonde Hair

Why do blondes have more fun? Because gentlemen prefer blondes.
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Why do gentlemen prefer blondes? Because they have evolved psychological mechanisms that predispose them to prefer women with blonde hair. Why?

The notion that blonde hair is the female ideal goes back at least half a millennium,
¹⁵
possibly a couple of millennia.
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There is evidence that women during the Roman era and the Renaissance period dyed their hair blonde, long before the discovery of peroxide in 1812. Women desired to be blonde so strongly throughout recorded history that they accomplished it without the aid of peroxide.

Some believe that men prefer blonde hair because blonde women tend to have lighter skin, which they prefer.
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But this seems to be false. While men do prefer women with lighter skin color,
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because it is an indication of higher fertility
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(a woman's skin color darkens when she is pregnant or on the Pill),
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the lightest skin color is associated with red hair, not blonde hair; yet, according to one study,
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both men and women have
extreme
aversion to potential mates with red hair. It turns out that men prefer blonde hair for exactly the same reason that they prefer large breasts: both are accurate indicators of a woman's age and thus reproductive value.

What distinguishes blonde hair from all other hair colors is that it changes dramatically with age. Young girls with light blonde hair usually grow up to be women with brown hair (although there are a very few women who retain their light blonde hair into adulthood). Thus, if men prefer to mate with women with blonde hair, they are unconsciously attempting to mate with younger (and hence, on average, healthier and more fecund) women with greater reproductive value and fertility. It is no coincidence that blonde hair evolved in Scandinavia and northern Europe, where it is very cold in winter. In Africa, where our ancestors evolved for most of their evolutionary history, people (men and women) mostly stayed naked. In such an environment, men could accurately assess a woman's age by the distribution of fat on her body or by the firmness of her breasts (as discussed above). Men in cold climates did not have this option, because women (and men) bundled up in such environments. This is probably why blonde hair evolved in cold climates as an alternative means for women to advertise their youth.
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Men then evolved a predisposition to prefer to mate with women with blonde hair in response, because those who did on average had greater reproductive success than those who did not, because, unbeknownst to them, they ended up mating with younger, healthier women with greater reproductive value and fertility.

Incidentally, this also suggests that the stereo type that blondes are dumb may have some statistical basis. Why do people believe that blondes are dumb? Recall that the human brain, including the stereo types that it generates, is adapted to the ancestral environment. What would be the average age of light blondes in the ancestral environment (say, northern Europe ten thousand years ago) in the absence of hair dye? Roughly 15. What would be the average age of brunettes in the same environment? Roughly 35. A 15-year-old woman is bound to be more naïve and less experienced, mature, and wise (in other words, “dumb”) than a 35-year-old woman, no matter what her hair color. It's not that blonde women are dumber than brunette women; it's that younger women are “dumber” (less knowledgeable) than older women, and blonde hair is a reliable indicator of extreme youth. The same logic is probably behind the stereo type that women with large breasts are dumb. In the ancestral environment, without plastic surgery or even bras, only very young women had large, firm breasts.

Blue Eyes

The typical description of ideal beauty always goes “blonde, blue eyes.” After Marlowe proposed a solution for the mystery of why men prefer women with large breasts, the attraction to blue eyes remained the only mystery to solve in the area of traits associated with physical attractiveness. We now knew why men preferred women with all the traits that characterize Barbie or a typical blonde bombshell, and we knew the evolutionary logic behind each of them. But eye color, more so than hair color, seems such an arbitrary trait. Why should women with blue eyes be any different from those with green or brown eyes? Yet a preference for blue eyes seems both universal and undeniable.
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There is an additional layer to the mystery of blue eyes. Unlike all the other traits discussed above, which are considered to be attractive
only
for women, blue eyes are thought to be attractive for both women
and
men. For instance, a typical description of an attractive man is “tall,
dark
, and handsome,” not blond; unlike blonde women, blond men are not universally considered to be attractive (because women generally prefer to mate with older, not younger, men).
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Yet, as the examples of Frank Sinatra (“Ol' Blue Eyes”) and Paul Newman show, men with blue eyes are considered to be attractive, just like women with blue eyes. So it appears that the answer to the question, “Why are blue eyes attractive?” must involve more than male sexual preference.

The attraction of blue eyes remained an evolutionary mystery until an undergraduate student, Lee Anne Turney, suggested a novel solution in her term paper for a class that she took from one of us (Kanazawa) in spring 2002. As far as we know, hers is the only available explanation for the attraction of blue eyes that anyone has ever proposed, and it has at least surface plausibility. But, of course, it will have to be subjected to rigorous experimental testing before it can become an accepted explanation.

Turney points out that the human pupil dilates when an individual is exposed to something that he or she likes.
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For instance, the pupils of women and infants (but not men) spontaneously dilate when they see babies. Thus, pupil dilation, which is usually beyond an individual's conscious volitional control, can be used as an honest indicator of interest and attraction. Most people are not even aware that the size of their pupils changes when they see something they like, so it would be difficult to deceive others by consciously manipulating their pupil size. We cannot help but reveal our interest in and attraction to others through the size of our pupils.

Turney then makes two simple observations. First, every human pupil is dark brown, regardless of the color of the iris, which encloses the pupil and determines the color of the eye. Second, blue is the
lightest
color of human iris. The consequence of these two observations is that
the size of the pupil is easiest to determine in blue eyes.
If you face people with different eye colors and must determine whether each person likes or is interested in you, with all else equal, it is easiest to read the blue-eyed person's level of interest or attraction. Turney's argument, which we believe might be true, is that blue-eyed people are considered attractive as potential mates because it is easiest to determine whether they are interested in us or not. It is easier to “read the minds” of people with blue eyes than of those with eyes of any other color, at least when it comes to interest or attraction.

One of the advantages of Turney's solution is that it not only explains why blue eyes are considered to be ideal in mates but also explains why, unlike all the other traits we discuss in this section, blue eyes are considered to be attractive in both sexes. It is just as important for women to read men's minds as it is for men to read women's; if anything, given the far greater consequences of making mistakes by being attracted to the “wrong” person, women should have a greater need to decide whether their potential mate's seeming interest in them is genuine or not. The negative consequences of being fooled by a lying suitor are much greater for women, so blue eyes should be a more important characteristic in men than in women.

Incidentally, we believe that Turney's logic can also explain why people with dark brown eyes are often considered to be “mysterious.” They are mysterious because their minds—that is, whether or not they are interested in or attracted to us—are more difficult to assess. The color of the dark brown iris is very similar to the (universal) color of the pupil, and so it is very difficult to gauge the size of the pupil in dark brown eyes. Many people, both men and women, express dislike for extremely dark brown eyes.
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