WHILE art historians agree that standards of beauty have changed over time—witness the plump shapes of Rubens, versus the svelte forms of Klimt—many scientists beg to differ. In particular, sociobiologists argue that aesthetic judgments, particularly about prospective mates, are deeply ingrained in human nature and are carried in our genes. But in this week's issue of Nature, Douglas Yu, a biologist at Imperial College, London, and Glenn Shepard, an anthropology student at the University of California, Berkeley, present findings that they hope will make the sociobiologists' arguments a mite less attractive.

Dr Yu's research builds on the work of Devendra Singh, a psychologist at the University of Texas at Austin. In 1993 Dr Singh found that when presented with standardised drawings of female body-types, men from a variety of different cultures preferred those with an hourglass shape. In particular, he found that men preferred a woman whose waist was 70% as wide as her hips, regardless of her total body mass.

Dr Singh suggested an evolutionary story to explain these findings. An hourglass shape in women is associated with relatively high levels of the hormone oestrogen. Since oestrogen levels influence fertility, men seeking to pass their genes to the next generation would do well to pick hourglass-shaped women. And any gene that encourages such behaviour would do better than one that did not.

Although Dr Singh's hypothesis paints a pretty picture, other researchers have seen flaws. Even if the results hold across cultures (and it is not certain that they do), how likely is it that such uniformity is due to nature, rather than nurture? If men really do prefer an hourglass shape, have they been programmed by their genes, or by their culture? As more of the human species is exposed to the same entertainment and advertising, it becomes increasingly hard to separate the two.

So Dr Yu travelled to a national park in south-eastern Peru, where he interviewed members of an isolated indigenous population. Although the 300 members of the park's Matsigenka people have come into contact with the outside world, exposure has been limited to researchers and “official visitors”. Dr Yu found that Matsigenka men preferred heavier body types to lighter ones, and more significantly for Dr Singh's hypothesis, preferred women with wider waists than the “western” norm.

These results cast some doubt on the universal applicability of Dr Singh's results, and suggest that culture, not heredity, may be the main influence on perceptions of female beauty. Even so, there could be a sociobiological explanation for the Matsi-genka's preferences. There might, for example, be an unusual feature of their environment that makes larger, wide-waisted women healthier or more fertile than their thinner counterparts. Dr Yu has tried to counter this potential objection by surveying two other populations of Matsigenka descent, both of which have had more contact with western influences. He found that as contact increased, men's preferences shifted rapidly to coincide with those of men in the United States. This would appear to undermine sociobiological explanations that rely on the slow work of natural selection.

The argument is far from over. But as Dr Yu points out in his article, it may not go on much longer. As globalisation works its magic, isolated groups such as the Matsigenka are becoming harder to find. The great hourglass debate is, sadly, running out of time.