Professor Maria da Graca Bicalho, head of the Immunogenetics and Histocompatibility Laboratory at the University of Parana, has said that people with diverse major histocompatibility complexes (MHCs) were more likely to choose each other as mates than those whose MHCs were similar.
And she said that this tendency was likely to be an evolutionary strategy to ensure healthy reproduction.
Previous studies have already shown females' preference for MHC dissimilar mates in many vertebrate species, including humans, and it is also known that MHC influences mating selection by preferences for particular body odours.
In the current study, the researchers decided to investigate mate selection in the Brazilian population, while trying to uncover the biological significance of MHC diversity.
They studied MHC data from 90 married couples, and compared them with 152 randomly generated control couples.
They also counted the number of 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, we 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," said Bicalho.
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.
It's known that genetic variability is an advantage for offspring,and scientists said that the MHC effect could be an evolutionary strategy underlying incest avoidance in humans and also improving the efficiency of the immune system.
"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," said Bicalho.
The scientists believe that the findings will help understanding of conception, fertility and gestational failures.
Bicalho will present the findings at the annual conference of the European Society of Human Genetics.