That strong odor turned raters off even with MHC-dissimilar men may be due to the fact odor is a useful indicator of disease. From diabetes to viral infection to schizophrenia, unusually sweet or strong body odors are a warning cue that ancestral females in search of good genes for their offspring may have been designed to heed. (In the case of schizophrenia, the issue is confounded—while some schizophrenics do actually have an unusually sweet smell, many suffer from delusions of foul smells emanating from their bodies.)
Nobody yet knows what roles MHC may play in male evaluations of female attractiveness. Females' superior sense of smell, however, may well be due to their need to more carefully evaluate a potential mates merits—a poor mate choice for male ancestors may have meant as little as a few minutes wasted, whereas a human female's mistake could result in a nine-month-long "morning after" and a child unlikely to survive.
Perfumers who really want to provide that sexy allure to their male customers will apparently need to get a genetic fingerprint of the special someone before they can tailor a scent that she will find attractive. But before men contemplate fooling women in this way, they should consider the possible consequences.
Fooling Mother Nature
The Swiss researchers found that women taking oral contraceptives (which block conception by tricking the body into thinking it's pregnant) reported reversed preferences, liking more the smells that reminded them of home and kin. Since the Pill reverses natural preferences, a woman may feel attracted to men she wouldn't normally notice if she were not on birth control—men who have similar MHC profiles.
The effects of such evolutionary novel mate choices can go well beyond the bewilderment of a wife who stops taking her contraceptive pills and notices her husband's "newly" foul body odor. Couples experiencing difficulty conceiving a child—even after several attempts at tubal embryo transfer—share significantly more of their MHC than do couples who conceive more easily. These couples' grief is not caused by either partner's infertility, but to an unfortunate combination of otherwise viable genes.
Doctors have known since the mid-1980s that couples suffering repeated spontaneous abortions tend to share more of their MHC than couples for whom pregnancies are carried to term. And even when MHC-similar couples do successfully bring a pregnancy to term, their babies are often underweight.
The Swiss team believes that MHC-related pregnancy problems in humans are too widespread to be due to inbreeding alone. They argue that in-couple infertility problems are due to strategic, unconscious "decisions" made by women bodies to curtail investment in offspring with inferior immune systems—offspring unlikely to have survived to adulthood in the environments of our evolutionary past.
When Broca and other social Darwinists pointed out that "uncivilized races" were more sensitive to body odor, they may have been correct—insofar as Europeans tend to go to greater lengths to perfume and wash away their natural scents. But this is hardly evidence of European superiority over "less evolved" peoples, as Broca insisted. Paying careful attention to the health of others and their suitability as sires to one's offspring in the disease-rich tropics, whose cultures Broca derided, actually makes exceedingly good sense.
Perfume; daily, soapy showers; convenient contraceptive pills—all have their charms. But they also may be short-circuiting our own built-in means of mate choice, adaptations shaped to our unique needs by millions of years of ancestral adversities. The existence of couples who long for children they cannot have indicates that the Western dismissal of body scent is scarcely benign.
Those who find offensive the notion that animal senses play a role in their attraction to a partner need not worry. As the role of smell in human affairs yields to understanding, we see not that we are less human but that our tastes and emotions are far more complex and sophisticated than anyone ever imagined.
How To Smell A Mate
How does body odor affect a woman's sexiness? Scientists don't know for sure, but they do know that a man's allure depends in part on how many immune system genes he shares with a potential mate.
Since it's known that women can detect genetic compatibility by smell—it's not that men can't but that so far no one knows—the onus is on females to sniff out a suitable squire.
Choosing a genetically compatible partner can be difficult it today's perfume rich postindustrial jungle, and getting your immune system genes profiled can be expensive. Before you run to a doctor for blood work to see whether your mate is a suitable match—and sire for your future children—try listening to your nose. (Unfortunately, the sniff test will only work if you're not taking birth control pills.)
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