Researchers have found that females often prefer mates with dissimilar major histocompability complex(MHC) in many vertebrate species, including humans, and that the MHC influences mating selection by preference for particular body odors.
The Brazilian team has been working in this field since 1998, and decided to investigate mate selection in the Brazilian population, while trying to uncover the biological significance of MHC diversity.
The scientists studied MHC data from 90 married couples, and compared them with 152 randomly-generated control couples. They counted the number MHC dissimilarities among those who were real couples, and compared them with those in the randomly-generated 'virtual couples'. If MHC genes did not influence mate selection, they would have expected to see similar results from both sets of couples. But they found that real partners have significant more MHC dissimilarities than they could have expected to find simply by chance.
The MHC is a large genetic region situated on chromosome 6, and found in most vertebrates. It plays an important role in the immune system and also in reproductive success.
Within MHC-dissimilar couples the partners will be genetically different, and such a pattern of mate choice decreases the danger of endogamy (mating among relatives) and increases the genetic variability of offspring. Genetic variability is known to be an advantage for offspring, and the MHC effect could be an evolutionary strategy underlying incest avoidance in humans and also improving the efficiency of the immune system, the scientists say.
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