http://www.psychologytoday.com/articles/pto-20071228-000001.html
Though we may remain partially oblivious to scent signals we’re sending and receiving, new research suggests that we not only come equipped to choose a romantic partner who smells good to us, but that this choice has profound biological implications. As we act out the complex rituals of courtship, many of them inscribed deep in our brain, scent-based cues help us zero in on optimal partners—the ones most likely to stay faithful to us and to create healthy children with us.
When you’re turned on by your partner’s scent, taking a deep whiff of his chest or the back of her neck feels like taking a powerful drug—it’s an instant flume ride to bliss, however momentary. Research has shown that we use scent-based signaling mechanisms to suss out compatibility. Claus Wedekind, a biologist at the University of Lausanne in Switzerland, created Exhibit A of this evidence by giving 44 men new T-shirts and instructing them to wear the shirts for two straight nights. To ensure that the sweat collecting on the shirts would remain “odor-neutral,” he supplied the men with scent-free soap and aftershave.
After the men were allowed to change, 49 women sniffed the shirts and specified which odors they found most attractive. Far more often than chance would predict, the women preferred the smell of T-shirts worn by men who were immunologically dissimilar to them. The difference lay in the sequence of more than 100 immune system genes known as the MHC, or major histocompatibility complex. These genes code for proteins that help the immune system recognize pathogens. The smell of their favorite shirts also reminded the women of their past and current boyfriends, suggesting that MHC does indeed influence women’s dating decisions in real life.
Women’s preference for MHC-distinct mates makes perfect sense from a biological point of view. Ever since ancestral times, partners whose immune systems are different have produced offspring who are more disease-resistant. With more immune genes expressed, kids are buffered against a wider variety of pathogens and toxins.
But that doesn’t mean women prefer men whose MHC genes are most different from theirs, as University of Chicago evolutionary biologist Martha McClintock found when she performed a T-shirt study similar to Wedekind’s. Women are not attracted to the smell of men with whom they had no MHC genes in common. “This might be a case where you’re protecting yourself against a mate who’s too similar or too dissimilar, but there’s a middle range where you’re OK,” McClintock says.
The few couples with a high degree of MHC similarity, however, suffered higher rates of miscarriage and experienced longer intervals between pregnancies, indicating more difficulty conceiving. Some scientists speculate that miscarriages may be the body’s way of curtailing investment in a child who isn’t likely to have a strong immune system anyway.
What’s more, among heterosexual couples, similar MHC profiles spell relational difficulty, Christine Garver-Apgar, a psychologist at the University of New Mexico, has found. “As the proportion of MHC alleles increased, women’s sexual responsiveness to their partners decreased, and their number of sex partners outside the relationship increased,” Garver-Apgar reports. The number of MHC genes couples shared corresponded directly with the likelihood that they would cheat on one another; if a man and woman had 50 percent of their MHC alleles in common, the woman had a 50 percent chance of sleeping with another man behind her partner’s back.
Lots more at the link. Found this relative and interesting.
