Why Opposites Attract

Opposites attract, runs the old adage.

Now scientists claim to have found out why.

A study has shown that women are programmed to seek out men whose immune systems are unlike their own.

The greater the difference there is in the genes which are key to the immune system, the more likely a woman will stay faithful.

But if the genes are very similar, a woman is more likely to be sexually dissatisfied with her partner, have a roving eye and even have an affair.

It is thought that seeking out a mate with a different immune system ensures any children the couple have will have the broadest immunity against disease.

The research could even lead to the creation of a DNA test which would show how likely a woman is to remain faithful.

And it could explain why famously ill-matched couples such as bookish playwright Arthur Miller and Hollywood wild-child Marilyn Monroe fall in love.

In the study, U.S. scientists analyzed the genes key to the immune system known as the major histocompatibility complex, or MHC of 48 couples who had been together for at least two years.

They 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.

The more similar a woman's immune system genes were to those of her partner, the less sexually attracted to him she was and the more likely she was to cheat, the researchers from the University of Mexico found.

However, when there were great differences in the genes investigated, women were much more likely to be faithful.

Further analysis of the results, published in the New Scientist, 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 percent chance the woman would cheat.

Male fidelity, however, did not seem to vary with genetics.

Clues to the makeup of a person's MHC, which is vital in controlling the way the immune system recognises invading bugs, are revealed in sweat.

Studies have shown the more different someone's sweat is from yours, the more pleasant you find them. It is thought the phenomenon evolved to prevent us unintentionally mating with relatives or others who are genetically similar to us.

It also ensures that any children produced have the greatest chance of fighting off disease.

Other studies have shown that going on the Pill blunts a woman's sense of smell and so her ability to pick the ideal mate.

This had led to suggestions that before committing to a man a woman should come off the Pill, so she can work out whether her beau is as attractive as she believes.

Source: Daily Mail (UK). Powered by Yellowbrix.