THE second half of the 20th century has produced many a dubious icon of female beauty, but one thing appears to unite them all 鈥� a talent for losing weight. Miss Americas of the 1980s were twice as skinny as those of the 1940s. And if present trends in Playboy 鈥渃entrefolds鈥� continue, the emaciated women who fill the pages early next century will be underweight to the tune of 20 per cent, relative to norms stated by nutritionists.
So is the idealised female shape becoming ever more androgynous and stick-like? Far from it. Despite all the determined shedding of adipose tissue, one vital statistic of the female beauty icon defies change: the ratio of waist to hip size. The Miss Americas and Playboy centrefolds of today may be skinnier than their counterparts of yesteryear but they share the same waist-to-hip ratio, and a narrow one at that. For women in the general population, the ratio can be a tubular 0.8 or higher. But the average for a Miss America or a Playboy centrefold has never been more than a decidedly waspish 0.68 to 0.72 (see Graphs).
Nor is it ever likely to be, according to Devendra Singh, a psychologist at the University of Texas, Austin, who has made an academic career out of studying the way people respond to female bodies of different shapes and sizes. To the dismay of those who say our tastes in body shapes are conditioned mainly by culture, Singh believes that humans have evolved an innate preference for female bodies with narrow waists set against full hips. It is a preference etched deep in the unconscious mind, he argues, a crucial part of an 鈥渦nconscious template of the prototype attractive female body鈥�, the mother of all beauty icons. And this template, he says, is a legacy of an evolutionary past when life was brutish and short and assessing the fertility of prospective mates was vital to producing offspring.
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Wasp waists: the people鈥檚 choice
The usual counter to such arguments is to hold up culture, in place of evolution, as the sculptor of human desires. Don鈥檛 wasp-waisted Miss Americas beget a demand for more wasp waists? Singh is sceptical. In the weary tones of one who has answered the same point at countless campus seminars, he argues that girlie mags, and in a different era bustles and corsets, may have accentuated the preference for wasp waists but they couldn鈥檛 have created it. The preference for female bodies with low waist-to-hip ratios transcends sex, age and the boundaries of Western magazine racks in a way that only the most contorted of cultural arguments could explain, he says.
To test this hypothesis, Singh shows volunteers a selection of line drawings or photographs of female bodies of various shapes and sizes, and then ask them to rank the images according to physical attractiveness. American men and women invariably rank female figures with low waist-to-hip ratios higher than ones with more tubular figures. So too, says Singh, do volunteers reared in non-Western cultures. His latest study, for example, looked at the body-shape preferences of a group of 71 Indonesian men and women who had recently arrived in the US as university students. Strict state censorship and a strong Muslim tradition in Indonesia mean that few people are exposed to magazines or movies showing scantily clad women.
The volunteers were shown line drawings of female figures with waist-to-hip ratios of 0.7, 0.8, 0.9 or 1.0, each in three body sizes-normal, underweight and overweight. Indonesian men and women found figures with the lower waist-to-hip ratios the most attractive. More than that, they rated overweight women with low waist-to-hip ratios (0.7 and 0.8) as just as attractive as underweight women with high ratios (0.9, 1.0).
The message from this kind of study, says Singh, is that body weight may not be as important as the fashion industry 鈥� and indeed much previous research into physical attractiveness 鈥� would have women believe. 鈥淭he idea that attractiveness can be measured on a single fat-thin continuum is wrong; shape is important, too.鈥� Another case of psychology confirming what many people have long taken for granted? 鈥淪ome of these trends were already known鈥�, says John Manning, a biologist at the University of Liverpool who also studies body shape. 鈥淏ut Singh has extended the research and trawled the literature to build a convincing case for waist-hip ratios being important in perceptions of attractiveness.鈥�
Why they should be so seems effortlessly obvious to Darwinian adaptationists, who argue that a low waist-to-hip ratio is a badge of reproductive fitness in women. Wasp waists equate with high levels of oestrogen and low levels of testosterone, a hormonal balance normally linked to high fertility. Consistent with this, women of reproductive age with high waist-to-hip ratios report having more difficulty becoming pregnant. And one other reason why people might be sensitive to waistlines is that they disappear early in pregnancy. Males duped into raising offspring devoid of their own genes are Darwinian failures.
But wait. Thin-waisted females haven鈥檛 always been fashionable, and still aren鈥檛 in some societies. As the paintings of Rubens along with innumerable anthropological studies attest, plump, thicker-waisted women sometimes rule the fashion podium. How do the adaptationists explain this? The obvious answer involves food resources. In societies awash with fat-laden food, thinness may become a badge worn by the gastronomically discerning elite; conversely, in societies where only the elite enjoy regular meals, it may be plumpness that signals wealth and social status. More to the point, say adaptationists, a critical amount of body fat is essential for ovulation, so plumper women are more likely to be able to sustain pregnancy and breast-feeding during a brief famine.
But there are other reasons why the equation 鈥渨asp waist equals high fertility equals attractiveness鈥� is too simplistic. Higher levels of testosterone, of the kind that thicken waists, might be bad news for conception but make up for it in other respects. They might increase libido, for instance. They might even bias the sex ratios of offspring in a favourable way.
Tubular women produce more sons
This idea comes from studies suggesting that women with high levels of testosterone are marginally more likely to produce sons than daughters 鈥� women, for example, who conceive early in the reproductive cycle when testosterone levels are highest (see 鈥淲hy presidents have more sons鈥�, New 杏吧原创, 3 December 1994). If testosterone really is the explanation for such biases, it follows that women with thicker waists should produce marginally more sons than daughters.
This is exactly what happens, according to Manning and his colleagues at the University of Liverpool, who have measured and weighed 84 mothers to see if their body shape or size is linked in any way to the sex of their offspring. In the researchers鈥� sample, women with thicker waists and higher waist-to-hip ratios had produced marginally more sons than daughters. 鈥淚f a woman has got a lot of testosterone, she鈥檒l have a high waist-to-hip ratio and lower fertility, but she鈥檚 also more likely to have sons,鈥� says Manning.
Harder to explain is why a tendency for thick-waisted women to produce sons, and thin-waisted women daughters, should be adaptive in a Darwinian sense. One widely cited theory suggests that when food is scarce, producing females may be the best way for animals to propel genes into future generations because malnourished females are more likely to find mates than are malnourished males.
But in the case of humans, Manning also highlights a social twist. In societies where rank is inherited by males, thick-waisted women may become fashionable because they are more likely to produce sons. 鈥淲hat is perceived to be the ideal body form for women may be an adaptive response to the way in which rank is inherited in human societies,鈥� suggests Manning.
Food resources, fertility signals, sex biases in offspring 鈥� how could these influences have conspired to produce the beauty icons of the late 20th century? In industrialised societies, males no longer have a monopoly on inherited rank, so producing sons is no longer a priority; nor is food in short supply for most people. In fact, quite the reverse. With these constraints lifted, wouldn鈥檛 you expect the 鈥渦nconscious template鈥� of the wasp-waisted beauty to reassert itself?
Perhaps. But it would be a rash person indeed who condoned those trends. While the beauty icons are becoming thinner, real women are putting on weight. The gap between idealised and real female figures is growing in a way that some individuals clearly feel powerless to control. Real women may also be becoming more tubular than the fashion icons, although nobody knows for certain as good data on trends in the general population are hard to come by. What is clear is that more and more women are seeking the help of surgeons to refashion their bodies. Would that we could refashion the legacy of our evolutionary past instead.