Genetic and educational assortative mating among US adults

Abstract

Understanding the social and biological mechanisms that lead to homogamy (similar individuals marrying one another) has been a long-standing issue across many fields of scientific inquiry. Using a nationally representative sample of non-Hispanic white US adults from the Health and Retirement Study and information from 1.7 million single-nucleotide polymorphisms, we compare genetic similarity among married couples to noncoupled pairs in the population. We provide evidence for genetic assortative mating in this population but the strength of this association is substantially smaller than the strength of educational assortative mating in the same sample. Furthermore, genetic similarity explains at most 10% of the assortative mating by education levels. Results are replicated using comparable data from the Framingham Heart Study.homophily | random mating | genetic homogamy A ssortative mating occurs when individuals exhibit a preference for those who are either similar, (homogamy) or dissimilar (heterogamy) to themselves. Two expressions-"birds of a feather flock together" and "opposites attract"-are used to explain friendship and spousal pairings but denote opposite assumptions regarding the direction of selection. Critically, no existing research has quantified the degree to which individuals who select into a marriage are genetically similar to one another across the entire genome.Quantifying genome-wide genetic assortative mating (GAM) in the population is important for methodological and substantive reasons. First, statistical models in genetic epidemiology, such as Hardy-Weinberg equilibrium, often assume random mating to forecast population allele frequencies, homozygosity rates, and other parameters of interest across generations (1) and behavior genetics models assume random mating to calculate heritability estimates (2). Second, social scientists have long studied the causes and consequences of assortative mating on a number of phenotypic measures such as height, education, religiosity, and political partisanship (3-5). Although there is research with a focus on the implications of genetic homogamy for phenotypic assortative mating (6), most studies of assortative mating have not considered the possibility that GAM may underlie phenotypic sorting. Social factors clearly limit opportunities to interact with people of different backgrounds (7, 8) but there is no study that simultaneously estimates educational assortative mating (EAM) and GAM in the population. Although much is known about changes in the nature of assortative mating over the past 50 y (5, 8, 9), little is known about the relationship between GAM and EAM.We focus on EAM because it has received the largest amount of attention in the assortative mating literature (4) and, equally important, research has shown that educational attainment reflects genetic influences (10,11). No existing study has used genomewide data among spousal pairs to quantify GAM in the population. This observation coupled with the potential bias caused by GAM in traditional...

Genetic and socioeconomic study of mate choice in Latinos reveals novel assortment patterns

“…Grouping couples by location, we found EAM scores from 0.09 to 0.17 in Mexicans and scores from 0.06 to 0.13 in Puerto Ricans. The magnitude of education assortment in Mexican and Puerto Rican couples was consistent with the education assortment in non-Hispanic whites measured by Domingue et al (11). Surprisingly, the GAAM scores were higher than the EAM scores in every location.…”

“…A recent study measuring genetic assortment in non-Hispanic white couples in the United States reported an assortment score of 0.045, which is substantially smaller than the GAAM scores of our populations (11). This difference could be due to the fact that the assortment score for the non-Hispanic whites was computed from genetic similarity rather than ancestry similarity, because all of the participants were of European ancestry (11). To make a more direct comparison, we analyzed the genotypes of the GALAI Mexican and Puerto Rican couples and computed the genetic assortative mating (GAM) scores using the same methodology as was used for non-Hispanic white couples (11).…”

“…Across Mexican and Puerto Rican populations in multiple locations, the GAAM scores ranged from 0.1 to 0.19. A recent study measuring genetic assortment in non-Hispanic white couples in the United States reported an assortment score of 0.045, which is substantially smaller than the GAAM scores of our populations (11). This difference could be due to the fact that the assortment score for the non-Hispanic whites was computed from genetic similarity rather than ancestry similarity, because all of the participants were of European ancestry (11).…”

“…We next sought to precisely quantify the magnitude of genomic ancestry assortment in couples and compare it with the magnitude of education assortment. To quantify the assortment of genomic ancestry while accounting for ancestry distribution at the population level in each location, we computed genomic ancestry assortative mating (GAAM) scores following the procedure proposed by Domingue et al (11). This score quantifies the magnitude of assortment above population background and can take a value from −0.5 (each person is paired with the most different partner) to 0.5 (complete assortment, where each person is paired with the most similar partner).…”

“…In Latinos, genotypes of ancestryinformative markers were shown to be positively correlated in partners (5). A recent study of non-Hispanic whites in the United States found that spouses were more genetically similar than random pairs of individuals; however, genetic assortment was substantially smaller than educational assortment in the same couples (11).…”