Finally -- a use for B.O. Some of the strangest evidence for the influence of airborne chemicals on human behavior comes from a bizarre funky tee-shirt experiment conducted in Switzerland. Zoologist Claus Wedekind gave 44 men a tee shirt and asked them to wear it for two nights in a row. He also gave them odorless soap and aftershave lotion, so artificial perfumes would not obscure their natural perfume.

Wedekind was following up on research showing that mice prefer to breed with animals with dissimilar immune-system genes. These so-called major histocompatibility complex (MHC) genes are a diverse group that produce chemicals that help the body detect and destroy foreign cells. In general, the more diverse the parent's MHC genes, the better the offspring's immune system will be.

Wedekind put the stinky shirts inside plain boxes and asked 49 women to evaluate their odor. Each woman sniffed seven boxes: three containing shirts from men whose MHC closely matched hers, three holding shirts from men with dissimilar MHC, and one holding a new shirt, as a control. The women responded as an evolutionary biologist might expect: They preferred the scent of men with dissimilar MHC. As if to prove that this finding was meaningful, many reported that the preferred scents reminded them of present or former boyfriends. In contrast, they found the shirts from men with similar MHC reminiscent of fathers and brothers. (See "Scent of a Man" in the bibliography). In fact, mothers can recognize the scent of their infants even if they have had limited contact with them. Furthermore, adults seem able to match, by smell alone, mothers and their children. Here's more on MHC and behavior. Not done yet One of the many intriguing findings from the mouse odor research that prompted Wedekind's work was a change in preference when the mouse became pregnant. To pregnant mice, opposites don't attract -- like does. Pregnant mice prefer animals with similar MHC genes, who were likely to be close relatives. It's easy to speculate, but difficult to prove, that the pregnant mice were trying to raise their reproductive odds by hanging out with family. Relatives, after all, share a common interest in having their genes perpetuated. It's entirely conceivable, of course, that humans would adopt a similar strategy, going outside the family to avoid inbreeding, and coming back to gain nurturing for the children. Oddly, Wedekind found evidence -- in the form of a spike in the data -- that this was occurring with his female subjects. Although most subjects preferred unlike MHC, women who were taking birth-control pills preferred men with similar MHC. Since estrogen levels rise in pregnancy, it's possible that the estrogen content of the pills made them, in some sense, "pregnant." Wedekind's watershed study raised many intriguing questions:

	Do men likewise prefer women with unlike MHC?
	Were the preferences caused by pheromones, by regular old scent, or both?
	Could women who are "on the pill" be chemically deluded in choosing mates?
	Just when you thought you'd need a $20-million biochemistry laboratory to dredge up a mate, along comes an old-style matchmaker. Look mom, no microprocessors!

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