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Attracted to That Healthy Glow? : Science: You think you're a sucker for a pretty face, but evolutionary biologist Randy Thornhill thinks what you're really going ga-ga over is a potent immune system.

November 22, 1994|MICHAEL HAEDERLE | SPECIAL TO THE TIMES

ALBUQUERQUE, N.M. — Prof. Randy Thornhill is studying the languorous, lingerie-clad form of Stephanie Seymour in a Victoria's Secret catalogue with clinical detachment.

The model's pouty lips and prominent cheekbones signal that she has high levels of estrogen, he observes. Ditto for the small lower jaw and overall flatness of her face.

Leafing through the rest of the catalogue, Thornhill finds confirmation of his theories of human beauty on every page.

"The models are just exaggerated forms of attractiveness that is on a continuum," he says. "They really all look alike when you account for hair color and eye color and that kind of stuff."

Thornhill, an evolutionary biologist at the University of New Mexico, thinks he knows why we see some women as beautiful and some men as handsome: They display traits--in some cases, influenced by hormones such as estrogen--that we are genetically predisposed to read as signs of a strong immune system. That, in turn, makes them more desirable as potential mates in the age-old battle to see whose genes survive.

It's a theory sure to make feminists and humanists grit their teeth.

Thornhill rejects the widespread view that influences such as TV commercials and Vogue fashion layouts have conditioned us to see certain people as attractive. Our notions of beauty, he believes, are largely innate.

"We know that people's judgments of faces are highly correlated," he says. "You can take pictures from people in one culture and show them to people in another culture and they will rank them the same way.

"There's clearly something going on with human nature with regard to attractiveness. We think we're getting it."

*

Thornhill, who at 49 looks a lot like Dick Clark, works out of a small office and lab in the UNM biology department. His desk is littered with papers, a plastic surgery text and the tools of his trade: calipers and a tape measure he uses on volunteer subjects.

A bumper sticker on a file cabinet reads, "Honk if you love Darwin."

His style is informal, and when he leans back in his chair to chat, his gently elongated vowels betray his Alabama roots. He's trying to quit smoking, and every so often he tucks a small pouch of smokeless tobacco in his cheek.

Thornhill belongs to a group of scientists who over the last 25 years have applied Charles Darwin's theory of evolution by selection to people and their behavior.

Modern Darwinists maintain that our primary purpose in life, whether we are aware of it or not, is to transmit our genes to our offspring. It's an imperative arising from millions of years of evolution.

Modern Darwinism is controversial because its emphasis on the role of genes in behavior seems to endorse stereotypical sex roles while implying that our actions are "programmed." (Men, according to Modern Darwinists, seek women who can bear many children, and may want to mate with as many women as possible to improve their reproductive odds. Women, on the other hand, are more apt to prefer men who will invest time and resources in helping to raise their young.)

But Thornhill says such objections are ill-founded.

"There's a lot of misunderstanding about the phenomenon of development," Thornhill says. "For any trait of the individual, both genes and environment are necessary to get the trait."

But why would we have evolved a preference for beautiful people in the first place?

In a word, parasites.

Some biologists think our evolution has been driven by competition with viruses, bacteria and other microorganisms that can produce millions of generations in the course of a human lifetime; each generation has a chance to evolve a new adaptation, posing a constant challenge to our immune systems.

People with greater diversity in their genes stand a better chance of evolving new ways to outmaneuver parasites. A key finding is that more genetically diverse individuals tend to have more symmetrical facial and body traits--such features as eyes, hands and feet.

During gestation, and throughout life, the development of these features can be disrupted by infections, toxins, malnutrition and other stresses. The more symmetrical these features are, Thornhill argues, the more they advertise a person's ability to resist diseases.

Thornhill and a colleague, evolutionary psychologist Steve Gangestad, noted in a 1993 paper (see story, E5) that qualities of averageness and symmetricalness were closely linked with attractiveness, especially in women. But there is another component to attractiveness: Decidedly non-average features, such as a large jaw and prominent cheekbones in men, are rated more attractive by study subjects.

Thornhill suspects this is because such exaggerated features develop during puberty under the influence of testosterone, which is known to suppress immune function. Thornhill reasons that a handsome man is advertising that his immune system is strong if it can withstand the effects of that extra testosterone.

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