Matching genes and a woman's sense of smell

Interesting articles on how women are biologically driven by their sense of smell when it comes to a man to whom they are attracted, and with whom they want to have children.

It appears that women can tell by smell whether a man is a good genetic match for her. A man who is genetically similar to a woman is not a good match, both in the ability to have children and in the chances the woman will cheat on the man. The findings were so predictive, that a DNA test could one day reveal how likely a woman is to cheat on her partner, the study suggests.

The team analyzed specific genes belonging to the major histocompatibility complex (MHC) – a set of genes that control the tags used by the immune system to differentiate between pathogens and cells belonging to the body.

The study revealed that as MHC genetic similarities increased, it was the women who were the most dramatically affected. They were less sexually responsive to their partners, more likely to have affairs, and more attracted to other males, particularly during fertile days of their menstrual cycles.

The fraction of MHC genes shared directly correlated to the woman's number of adulterous partners – if the man and woman had 50% of the MHC genes in common, the women had a 50% chance of cheating with another man, on average.

Men were an entirely different matter, the study showed. They did not seem to be affected by genetics at all. As MHC similarities increased, men showed no change in the sexual interest that they had for their partners and seemed no more attracted to women outside of their primary relationship.

Garver-Apgar and her team suggest that the MHC targets human behaviors, essentially controlling sexual attraction, perhaps in order to help to produce offspring with a broad spectrum of immunity.

“We’re fairly certain that all of this revolves around scent,” she adds. “Now all we have to do is track down the specific chemical cocktail responsible for all the behaviors we are seeing.”

For more info, click here to read the full article.

Also interesting is a study on how the Pill affects a woman's sense of smell.

Does taking the Pill disrupt a woman's animal instincts when it comes to choosing the perfect partner to father her babies?

A group of women were asked to sniff T-shirts that had been worn by a group of unknown - and unwashed - men. All they had to do was say which shirts smelled best. The experiment, run by Claus Wedekind, a young Swiss scientist then at the University of Bern, was designed to find out if humans, like mice, use body odor to identify genetically appropriate mates.

Given the choice, females sniff out mates with genes for immunity that differ from their own, and that this seems to increase their chances of producing healthy offspring. But among Wedekind's volunteers there was a startling exception to this trend. Women on the contraceptive pill showed the reverse preference. Instead of being attracted to the scent of dissimilar men, they chose men whose genes for immunity were closest to their own.

If women are using smell to find a good partner for reproduction, and the Pill is turning things upside down, then there could be serious consequences. By tricking users into falling for the wrong guy, the Pill could be giving women better protection than they bargained for - making it harder for them to have kids long after they stop taking it.

If olfactory cues about MHC genes are so important, why do women taking the Pill seem to respond so differently from other women? "My guess is that the Pill simulates pregnancy and that maybe during pregnancy, odor preferences change," says Wedekind. The theory is that during pregnancy, a female is attracted to the smell of her own relatives, who have similar MHCs to her own. After all, family members have the greatest interest in seeing her offspring survive. Pregnant women - and women whose bodies are tricked into thinking they're pregnant - might have the same tendency, says Wedekind.

The article goes on to test Hutterites...

Geneticist Carole Ober from the University of Chicago has been studying Hutterites for over a decade.

Hutterites are the perfect study group for "natural" mate choice among humans. They are a socially isolated group who work on communal farms, marry within their own community, and can trace their roots back to a handful of European ancestors in the 16th century. Single men and women visit neighboring Hutterite colonies, and often end up working or celebrating special occasions alongside potential spouses. They don't use perfumes or deodorants. "They are absolutely maximizing the importance of MHC," says Ober. They marry once -divorce is strictly prohibited - and, claims Ober, they marry for love. Once paired off, they place a high value on big families, and seldom use contraception.

Ober's group concludes that genes in this region of DNA may indeed influence mate choice in humans.

The next question for Ober was whether couples with similar MHCs actually have reduced fertility. Some of her early research on Hutterites had hinted that couples who had a large number of MHC matches took longer to conceive. She decided to look at this effect more carefully, asking 111 Hutterite women to keep diaries recording all their menstrual periods.

Of the 111 women, 27 had miscarriages, and there were 38 miscarriages altogether. None of the couples was completely infertile -all but one had already had at least one child, and none had more than two consecutive miscarriages. But when Ober scrutinized the MHC genes from the women and their husbands at 16 separate genetic sites, she found that miscarriage rates were highest for couples who matched at all these sites. And there was an increased risk even where there was matching at just some of the sites.

Martin Vessey, an epidemiologist at the University of Oxford, says, "Studies haven't suggested an association between fetal loss and Pill use." But then, no study has looked specifically at women who found life partners while on the Pill, he admits. And it's only recently that women have been using the contraceptive pill from such a young age - sometimes from before their first sexual encounter straight through to the time when they want to have kids.

More on smell...

As far as anyone can tell, whatever chemical signals do pass between people are subconscious. Nonetheless, Rachel Herz from Brown University in Providence, Rhode Island, decided to ask people about it directly. She polled 166 women about what makes a man attractive - specifically, attractive enough to go to bed with. Out of a variety of factors, including appearance, the sound of his voice and how his skin feels, women respondents said that a man's scent was paramount. Body odor was particularly important, the volunteers reported, in decisions not to have sex with a certain individual.

Herz suggests that if you are on the Pill and meet someone you want to have children with, you should stop taking oral contraceptives. "Go off," she says, "to see if you're still attracted.

For more info, click here to read the full article.

Interesting... it seems I have read how in the modern times it seems like more women in the developed countries are having trouble conceiving and are miscarrying more than years ago. Some thought this was because women are marrying later in life (the odds of conceiving decrease the older a woman is), and because of the stress of modern life. Yes, women are marrying later in life, but I can argue that life in the "good old days" was pretty stressful.

The moral appears to be... in order to have children and a wife who will not cheat, it is better to let the woman with a good sense of smell choose her mate, and she should do so when she is not on the Pill.