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Trends in marriage don’t affect population genetics, study shows

couple-35682_1280Ironically, while driving to work this morning I was thinking about the first time I spotted my future husband. At the time, I would have been shocked to learn we'd end up married, and I certainly wasn't thinking about population genetics.

But a team of researchers, including Stanford's Ben Domingue, PhD, have been thinking about the population-level effects of individual mating choices, and they published a paper this week in the Proceedings of the National Academy of Sciences. As Domingue, the study's senior author and an assistant professor of education, explains in a Stanford press release:

We’re asking how spouses are alike, how this is affecting the number of children they have, and then asking how both of these are changing over time... We see an increasing stratification across society in terms of mating and fertility, but it’s not corresponding to changes in the underlying genetic signature.

For example, tall people are more likely to marry each other. Those with more education are also more likely to wed others with degrees. Despite these trends, the researchers couldn't find a correlation between these traits and changes in the prevalence in the general population of genetic markers associated with these traits. First author Dalton Conley, PhD, dean for social sciences at New York University, explains:

While there is a tendency for people who are genetically similar along key dimensions to marry each other, there does not seem to be any increase in this tendency, despite what some people may fear about inequality getting baked into our genes... Ditto for how many kids folks are having – while there are genetic associations, they appear to be stable over time.

A key caveat: The team examined only white, married couples in their first marriage. They used data on 4,686 couples with at least one spouse born between 1919 and 1955. Traits considered included height, weight, mental health status, number of children and years of education.

Despite the trends in mate choice, the population's genetics hasn't changed, Domingue says:

If you just look at how people select for similar spouses, you might think there are changes in how genetics are related to decisions regarding marriage and fertility... Our point with this study is that none of the trends in the observed traits, height, for example, seem to be associated with changes in the relevant genetics. If we just had the phenotypic information and we tried to use that to infer what was happening genetically, we may get the wrong answer.

Previously: Epigenetics controls social dominance in African fishUsing genetics to answer fundamental questions in biology, medicine and anthropology and From whence the big toe? Stanford researchers investigate the genetics of upright walking
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