The secret to finding true love may lie in genetic differences

Immune system DNA could influence mating

People are more likely to become lovers if their genes share little in common, according to a study that demonstrates a possible biological mechanism controlling the sexual attraction between men and women.

Heterosexual men and women with dissimilar genes are more likely to get married than people with a similar genetic heritage. The findings indicate that certain genes control some of the subconscious desires behind the choice of one partner over another, as a way of preventing inbreeding and boosting a child's immune defences.

Researchers studied the genes of 90 married couples and found that their DNA in a key region of their chromosomes was significantly different compared with the same stretch of DNA in 152 couples chosen at random from the population and who were neither married nor having sexual relations with one another.

The genes, called the major histocompatibility complex (MHC), are part of the immune system. This is the first rsearch of its kind showing that they may play a significant role in whether or not couples are likely to get married.

If the MHC genes played no role in the choice of a mate, then the scientists would expect to find similar differences between both sets of couples – the married and the unmarried. However, the statistically significant difference suggests that the dissimilar MHC genes influenced whether men and women become attracted to one another.

"Although it is tempting to think that humans choose their partners because of their similarities, our research has shown clearly that it is differences that make for successful reproduction, and that the subconscious drive to have healthy children is important when choosing a mate," said Professor Maria da Graca Bicalho of the University of Parana in Brazil.

"We expect to find that cultural aspects play an important role in mate choice, and we certainly do not subscribe to the theory that if a person bears a particular genetic variant it will determine his or her behaviour," she said. "But we also think that the subconscious evolutionary aspect of partner choice should not be overlooked.

"This has an important role to play in ensuring healthy reproduction, by helping to ensure that children are born with a strong immune system better able to cope with infection."

It is possible that in addition to helping the body fight off diseases, the MHC genes have a subtle effect on body scents or pheromones which might in humans play a part in deciding whether a man or a woman is subconsciously considered to be attractive to an individual of the opposite sex.

"Pheromones play an important role in mammalian social behaviour. In humans, this has been more complex and questions like 'What draws people of the opposite sex together?' are still waiting for more investigations and answers," Professor Bicalho said.

The study does not, sadly, mean that scientists are able to say with any certainly whether one individual would fall in love with another.