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THE STRANGEST SPECIES

Forget the Look of Love--It's the Scent

May 13, 1996|KATHLEEN KELLEHER | SPECIAL TO THE TIMES

After the battle of Marengo, Napoleon reportedly sent word to Josephine: "Will be home in three days . . . don't wash."

Would the dictator covet eau de Josephine as an aphrodisiac in today's culture? Nah. And Josephine--anticipating her husband's return--would probably engage in rounds of aromatherapy and elaborate cleansing rituals to deep-six all traces of B.O. in an ozone-destroying cloud of scented soaps, deodorants, powders and perfumery.

But while we live in a postmodern perfume culture where scents are touted as transcendental (Obsession, Ecstasy), some evidence suggests that, like animals and insects, human beings exchange messages through body odors and chemical compounds. There is still some debate among scientists about whether humans emit pheromones--airborne chemicals that communicate important information--but a growing number of researchers claim evidence suggests that we do.

Scientists have long acknowledged the existence of pheromones in animals. Best known is the sex pheromone, secreted in sweat, urine, saliva and breath. Perfumers have extracted the stuff for pricey perfumes: musk from deer, civet from cats and castoreum from beavers. Works fine for animals, but forget about getting a hubba-hubba response from humans. Pheromones are species-specific.

A boar spits on a sow and she humps her back, spreads her legs and offers her posterior. The pheromone-rich urine of male prairie voles kick-start a female vole's reproductive machinery. A female Chinese silkworm moth attracts male moths from up to six miles away with pheromones. Mice check out the genetic eligibility of potential mates by sniffing their urine, the odor of which is influenced by an immune system gene called major histocompatibility complex, or MHC.

Odor preference in randy mice led one researcher to speculate about its effect in humans. To explore the dynamic in humans, thought to be largely unconscious, Claus Wedekind, an evolutionary psychologist at Bern University in Switzerland, went to that stench factory of glands--the armpits.

Wedekind asked 49 women to sniff sweaty T-shirts worn for two days by 44 non-showering, non-deodorized, garlic-avoiding guys and rate the smells on "pleasantness and sexiness."

He expected that the women would celebrate vive la difference, finding the odors secreted by men with the most dissimilar MHC more pleasant. In biology if not in logic, opposites attract.

Odors of T-shirts worn by MHC-dissimilar men reminded women test subjects of their mates or ex-mates twice as often as those worn by MHC-similar men. Conversely, T-shirts worn by men with similar MHC genes were described as unpleasant. Like mice, the women (and Wedekind thinks men may have the same preference) found the body odor emitted by MHC-dissimilar men pleasing. The evolutionary purpose, Wedekind says, is to ensure offspring with the most disease-resistant immune system, achieved by mating with someone whose MHC is most dissimilar. Rejecting mates with similar MHC genes also increases fertility and avoids inbreeding.

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Unlike other animals, humans don't exude the sex pheromones, say Wedekind and most scientists. Human pheromones work in more subtle ways (sweaty T-shirts did not make the women amorous) and require relatively long periods of exposure.

Our biological e-mail falls under the category of primer and signaler pheromones. Primer pheromones seem to affect the neuroendocrine system. In a 1986 study, women with irregular periods moved toward regular cycles after their upper lips were daubed repeatedly with a mix of odorless male underarm sweat extract. Within four months, a different study found that the menstrual cycles of women living together adjusted to start within four days of each other after several months of cohabitation.

Signaler pheromones provide information about identification, health, gender and age. Certain scents are associated with diseases such as diabetes and cancer. Other studies show that a mother's odor is imprinted upon an infant within a few hours of birth and that the mother, in turn, is encoded with her infant's smell within days of birth. Husbands and wives recognize each other by scent, and humans can identify kin by odor.

Not every culture has declared war on B.O. Today, in parts of Greece and the Balkans, there is a tradition in which men dance with a handkerchief tucked into the armpit, presenting their scent to their favored gal. She is supposed to swoon for him under the sexual spell of his, uh, manly-manness.

Some Australian aboriginals also have an armpit ritual, says Barbara Sommerville, a veterinary physicist at Cambridge University. "When they bid farewell, they wipe their armpits with their hands and then anoint each other's chest with it . . . to promote social bonding and as a form of identification," Sommerville says. "It is like animals marking each other."

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