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Opposites Attract In Human Pairing

May 25, 2009

A Brazilian study has found that people are subconsciously more likely to choose a partner whose genetic make-up is different to their own, further cementing the adage that opposites really do attract, Reuters reported.

Married couples were found to be more likely to have genetic differences in a DNA region governing the immune system than were randomly matched pairs, the researchers said.

Maria da Graca Bicalho and her colleagues at the University of Parana in Brazil reported that this was likely to be an evolutionary strategy to ensure healthy reproduction because genetic variability is an advantage for offspring.

Bicalho said although it may be 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,” she added.

It is still unknown exactly what signals attract the body to people who are genetically dissimilar to themselves, but scientists suggest body odor or even face structure could play a role.

Some studies suggest that animals are attracted to members of the opposite sex with differences in major histocompatibility complex or MHC, an immune system factor that also plays a role in having healthy offspring.

Bicalho’s team compared genetic data from 90 married couples with data from 152 randomly generated control couples and found the real couples had significantly more dissimilarities in MHC.

They wrote in a summary prepared for the conference of the European Society of Human Genetics in Vienna on Monday that parents with dissimilar genetic regions could provide their offspring with a better chance to ward infections off because their immune system genes are more diverse.

Bicalho said if MHC genes did not influence mate selection they would have expected to see similar results from both sets of couples.

“But we found that the real partners had significantly more MHC dissimilarities than we could have expected to find simply by chance.”

She added that the 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.

Studies in the past have suggested animals may use body odor as a guide to identify possible mates as being genetically similar or dissimilar, but other physical factors may also be involved.

Bicalho believes other cues such as face symmetry might play a role as well, but they are still in the field of speculation.

“We intend to follow up this work by looking at social and cultural influences as well as biological ones in mate choice, and relating these to the genetic diversity of the extended MHC region”, she said.

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