Women cheat more when their partners genes are similar

Women are more likely to cheat on their partners when they have more similar MHC genes (related to immune system).


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Don't pair up with matching genes

11:30 05 January 2007
NewScientist.com news service
Matt Kaplan

They say opposites attract – and a couple’s differences may be key to lasting happiness, according to a new genetic study of people in relationships. 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.

Psychologist Christine Garver-Apgar at the University of New Mexico in Albuquerque, US, and colleagues investigated whether genetic similarities among romantically involved couples predicted how faithful and sexually responsive the partners were to one another.

The team analysed 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. Previous research has shown that the MHC plays a role in sexual attraction, but its lasting role in a long-term relationship has not been investigated.

“There have been a number of studies that tested whether MHC similarities played a role in attraction, some involving sweaty T-shirts that women were actually asked to smell,” says Garver-Apgar. “What we wanted to know was whether or not these discoveries had any implications for romantically involved couples.”
Cheating chance

Garver-Apgar and colleagues carried out a genetic analysis of 48 heterosexual couples who had been in an exclusive relationship for at least two years. And the participants were then asked a series of questions about their relationship, including their sexual responsiveness towards their partner and their unfaithfulness in the relationship.

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, Garver-Apgar says. In relationships where MHC genetic differences were significant, these potentially relationship-splitting behaviours were either absent or greatly reduced.

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.
Chemical cocktail

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 behaviours, 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 behaviours we are seeing.”

Journal reference: Psychological Science (vol 17, p 830)