Major Histocompatibility Complex And Human Mating Systems

Human mating systems are mediated by many different variables, from cultural preferences to religious alignments. In some places, people marry and mate within their class or ethnic group. But there are more subtle, almost subliminal conditions behind mating that often affect the outcome of genetic variation and evolution. While I was out of the country, a paper was published in PLoS Genetics which outlined one of these conditions — mate choice and the major histocompatibility complex.

If you haven’t taken an immunology or molecular biology course, you may not know what the major histocompatibility complex (MHC from now on) is. The MHC is the most gene dense region of the mammalian genome and encodes for a lot of proteins act which act as signposts on the cell. These proteins are a crucial part of the autoimmune system. These signposts identify cells as self or foreign to the immune system, ultimately making MHC’s a critical part of disease-resistance. As Dienekes summarized, the evolutionary implications are pretty profound,

“couples dissimilar in [MHC genotype] will produce heterozygous children that will be more capable of fighting disease.”

The three authors of, “Is Mate Choice in Humans MHC-Dependent?,” asked whether or not couples differ more or less in the MHC region of the genome they do across the entire genome? Their testing employed genome-wide genotype data and HLA types in a sample of Yoruban and a sample of European American couples. This allowed them to distinguish MHC-specific effects from genome-wide effects. The group examined whether husband-wife couples were more MHC-similar or MHC-dissimilar in comparison to random pairs of individuals.

Surprisingly, the African couples were not more MHC-similar nor MHC-dissimilar. But across the genome, they were more similar than random couples. How could this be? This could possibly be due to social factors, i.e. mating with genetically close individuals that are within social units, rather than with individuals from the entire population.

European American couples, however, were predominantly MHC-dissimilar. They were drastically so in comparison to the genome, supporting the hypothesis that the MHC influences mate choice in this population. Does this mean that there’s been some sort of evolutionary pressure for Europeans to have more heterozygosity at MHC loci? I’d venture to say yes, epidemics like the Black Plague severely affected European populations but that’s not to say African’s have been disease free. As you may know malaria has constantly been a problem. More studies need to be conducted in other African populations with different mating patterns to fully consider if biological traits like MHC genotype play a significant role beside social traits in the process of mating.

    Raphaëlle Chaix, Chen Cao, Peter Donnelly, Molly Przeworski (2008). Is Mate Choice in Humans MHC-Dependent? PLoS Genetics, 4 (9) DOI: 10.1371/journal.pgen.1000184

3 thoughts on “Major Histocompatibility Complex And Human Mating Systems

  1. “In a less direct way, other studies have
    focused on odor preferences: in ‘‘sweaty T-shirts experiments’’, in
    which females were asked to smell T-shirts worn by different
    males, it was shown that females significantly prefer the odor of T-
    shirts worn by MHC-dissimilar males, although such preference
    was not found among females taking the contraceptive pill [24,25].”

    Hmmmm…does that mean that IF MHC is involved in mate selection that women who are on birth control pills may be picking incompatible mates??????

    Inquiring minds want to know!

    This may explain the massive divorce rate!

  2. I think that “bad mate selection” is a concern, but the research to back up a claim like that isn’t in place yet. I’m not sure, though, that it would tell us anything about divorce rates, since MHC is only going to be an indicator of genetic compatibility, not the sort of overall compatibility that leads to successful marriages. It might tell us something about fertility issues, though.

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