Brazilian scientists say they have discovered how humans choose their partners - they say opposites attract and genetics influence how a person chooses a partner.
According to Professor Maria da Graça Bicalho, head of the Immunogenetics and Histocompatibility Laboratory at the University of Parana, Brazil, people with diverse Major Histocompatibility Complexes (MHCs) were more likely to choose each other as mates than those whose MHCs were similar, and that this was likely to be an evolutionary strategy to ensure healthy reproduction.
The Brazilian team has been working in this field since 1998 and they say a females' preference for MHC dissimilar mates has been shown in many vertebrate species, including humans, and it is also known that MHC influences mating selection by preferences for particular body odours.
The researchers decided to investigate mate selection in the Brazilian population, while trying to uncover the biological significance of MHC diversity - this involved studying the MHC data from 90 married couples, and then comparing them with 152 randomly-generated control couples - they counted the number of MHC dissimilarities among those who were real couples and compared them with those in the randomly-generated 'virtual couples'.
Professor Bicalho says if MHC genes did not influence mate selection, similar results would have been expected from both sets of couples - it was in fact found that the real partners had significantly more MHC dissimilarities than could have been expected simply by chance.
The scientists say 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.
They say 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 researchers say the MHC is a large and extraordinarily diverse genetic region situated on chromosome 6, and found in most vertebrates and it plays an important role in the immune system and also in reproductive success.