A new study has revealed that while choosing a partner, American couples tend to look for new immune genes, whereas, Africans prefer to stick to the ones they have got.
According to the study, American couples of European ancestry seek mates with versions of immune genes, which are part of the major histocompatibility complex, that recognise pathogens dissimilar from those their own genes recognise.
And the more MHC genes a person has, the greater variety of pathogens his or her immune system recognises.
Earlier study in fish, lizards and birds has suggested that animals seek out mates with different MHC genes than their own. Still studies in humans have painted a far blurrier picture of MHC-driven mating preferences.
On of the studies, deduced that Hutterites, who live communally, marry people with different versions of the genes, while there wad one that found women prefer the scent of sweaty T-shirts worn by men with similar MHC genes.
But, one more additional sweaty T-shirt experiment using slightly different methods revealed just the opposite trend.
"It seems that body odours can reveal someone's immune genetics, and so through the smell we could be able to distinguish the MHC genes from different potential mates," New Scientist quoted Raphaelle Chaix, a human population geneticist at the National Centre for Scientific Research in Paris, France, as saying.
Instead of smelly T-shirts, researchers at University of Oxford studied previously gathered genetic data on 30 Caucasian couples from Utah and 30 Yoruba couples from Nigeria.
For the study, they analysed about 9000 genetic differences within the MHC genes, as well as more than 3 million differences dotted across the rest of their genomes.
This indicated that the American couples are selecting mates, in large part, based on MHC genes. However, in case of Yoruba couples, who seemed to pick mates with MHC genes no more different than would be expected for any two people picked at random from the population.
Scientists attributed the different findings to diversity. Overall, Yoruba people had more differences in their MHC genes than Americans, so there could be less evolutionary pressure to find a mate with new genes.
Culture may also play more of a role in mate choice for Africans. Among Yoruba, marriages between distantly related couples from socially connected clans could be more common than marriage between completely unrelated men and women.
"We can think that maybe two lineages will prefer to exchange their wives. In several generations, you can create in such a way a pattern where husband and wife are more similar than random individuals," said Chaix.