NEW YORK (GenomeWeb News) – Biological factors influence mate selection in some — but not all — human populations, new research suggests.
A team of researchers from the UK, China, and France used genotyping and other analyses to assess 30 African and 30 European-American couples. The results, appearing online today in PLoS Genetics, suggested that biology had a greater influence over mate selection in the European-American couples tested. On the other hand, coupling patterns in the African couples seemed to be more closely tied to socio-demographic factors.
Several animal studies have suggested that major histocompatibility complex, or MHC, signals can influence mate selection, with individuals picking up MHC information from potential mates’ body odor. By selecting mates with MHC profiles that are different from — or similar to — their own, animals may either increase the diversity of antigens that their offspring inherit or optimize those antigens.
But there’s little agreement about whether MHC signals influence mate selection in humans. For instance, women smelling sweaty T-shirts worn by a variety of men generally preferred those worn by men with dissimilar MHC types — a biological strategy that could increase the genetic diversity of their children’s immune system. But that did not hold true for women taking the contraceptive pill.
And, in another study, when women unknowingly sniffed sweaty T-shirts worn by men from ethnic backgrounds different from their own, they tended to prefer the smell of individuals sharing at least some of their own human leukocyte antigen, or HLA, alleles.
Population-based studies have also proved puzzling.
“Several studies have reported a tendency for humans to prefer MHC-dissimilar mates, a sexual selection that would favor the production of MHC-heterozygous offspring, who would be more resistant to pathogens, but these results are unsupported by other studies,” the authors wrote.
For the latest study, the researchers used genotyping and HLA typing to look at the similarities and differences in six HLA genes in the MHC region of the genome in 30 African and 30 European-American couples from the HapMap II dataset.
“[I]t is very rare for population geneticists to have access to genetic data for both husbands and wives,” lead author Raphaëlle Chaix, a researcher affiliated with the University of Oxford and Paris’ Musee de l’Homme, told GenomeWeb Daily News in an e-mail message. “Most of the time, in human population studies, only unrelated males are sampled, and such analyses are not possible.”
The researchers looked at 9,010 SNPs in the MHC region of the genome for individuals from each couple, who came from a Mormon population in Utah or a Yoruban population in Nigeria. They also assessed more than 3.2 million genome-wide SNPs.
By looking at similarities and differences in the HLA region and in the genome as a whole, the team was able to tease apart socio-demographic and biological influences on mate selection. “[G]enome-wide signatures are shaped by demographic and social factors whereas localized genomic signatures are shaped by selective pressures,” Chaix explained.
Consistent with the notion that MHC genetic variation can influence mate selection in some populations, the team found that the European-American couples tested had dissimilar MHC profiles. Genome-wide, though, members of those couple were no more similar than any other two individuals in the population.
In contrast, the MHCs in African couples did not appear to be more or less similar than those in other individuals. Instead, the African couples tended to share genome-wide patterns with their partners. African individuals sampled also had more diverse SNPs in the MHC region of the genome than their European-American counterparts.
The population-related differences were not surprising, Chaix said, adding, “Social factors are also very important in mate choice and we can expect that their importance depends on the population and outweigh more or less the biological factors involved in mate choice.”
There are several potential explanations for these population differences. For example, the authors speculated that the lack of MHC dissimilarity in Yoruban couples may reflect high pathogen pressure in this population. That could lead to mate selection for optimal, rather than dissimilar, HLA alleles. On the other hand, Chaix noted, “it is possible that because of the high level of MHC diversity in Yorubas, people do not need to choose a mate so different at the MHC level.”
While intriguing, Chaix emphasized, the new data only represents two populations. By looking at couples from other ethnic backgrounds and social patterns, the researchers hope to gain a broader understanding of the roles of biology and social factors in human mate selection. To that end, Chaix said the team is currently studying populations in Central Asia.