When opposites attract, it's just genes at work

Women Genetically Pre-Programmed To Seek Men Different From Themselves

It is an age old adage that opposites attract - now scientists believe they have found out why this is the case. A study has shown women are genetically pre-programmed to seek out men who are different to themselves.

It is thought that seeking out a mate with different genes - and therefore a different immune system - ensures any children the couple will have the broadest possible protection against disease. If the genes are very similar, a woman is more likely to be sexually dissatisfied with her partner, have a roving eye - and even an affair.

The research published, in this week's NewScientist Magazine could even lead to the creation of a DNA test which would show how likely a woman is to remain faithful.

In the study, US scientists analysed the major 'histocompatibility complex' genes - those which are key to the immune system - of 48 couples who had been together for at least two years.

The men and women were then asked a series of questions about their relationship, including whether they had been unfaithful and how sexually attracted they were to their partner, scientists found a key link between genes and fidelity.

The more similar a woman's immune system genes were to those of her partner, the less sexually attracted she was to him and the more likely she was to cheat. And the risk of infidelity was greatest on the days when a woman was most fertile, the University of New Mexico researchers found.

However, when there were great differences in the genes investigated, women were much likely to be faithful. Analysis of the results revealed that the percentage of shared genes directly correlated to a woman's fidelity. For instance, if a man and woman had half of their MHC genes in common, there was a 50% chance that the woman would cheat with another man.

Male fidelity, however, did not seem to vary with genetics. The MHC is vital in controlling the way the immune system recognises invading bugs and clues to the make-up of a person's MHC are revealed in sweat.

Previous studies have shown that the more different someone's sweat is to yours, the more pleasant you find them - and their sweat. It is thought the phenomenon evolved to prevent us unintentionally mating with relatives - or people genetically similar to us. It also ensures that children produced have the greatest possible chance of fighting off disease.