Scientists already knew that people tend to marry
others who have similar characteristics, including religion, age, race, income,
body type and education, among others.
In the new study, published in the journal
Proceedings of the National Academy of Sciences, scientists show that people
also are more likely to pick mates who have similar DNA. While characteristics
such as race, body type and even education have genetic
components, this is the first study to look at similarities across the entire
"It's well known that people marry folks who are
like them," said Benjamin Domingue, lead author of the paper and a research
associate at CU-Boulder's Institute of Behavioral Science. "But there's been a
question about whether we mate at random with respect to genetics."
For the study, Domingue and his colleagues,
including CU-Boulder Associate Professor Jason Boardman, used genomic data
collected by the Health and Retirement Study, which is sponsored by the National
Institute on Aging.
The researchers examined the genomes of 825
non-Hispanic white American couples. They looked specifically at
single-nucleotide polymorphisms, which are places in
their DNA that are known to commonly differ among humans.
The researchers found that there were fewer
differences in the DNA between married people than between two randomly selected
individuals. In all, the researchers estimated genetic similarity between
individuals using 1.7 million single-nucleotide polymorphisms in each person's
The researchers compared the magnitude of the
genetic similarity between married people to the magnitude of the better-studied
phenomenon of people with similar educations marrying, known as educational
assortative mating. They found that the preference for a genetically similar
spouse, known as genetic assortative mating, is about a third of the strength of
educational assortative mating.
The findings could have implications for statistical
models now used by scientists to understand genetic differences between human
populations because such models often assume random mating.
The study also forms a foundation for future
research that could explore whether similar results are found between married
people of other races, whether people also choose genetically similar friends,
and whether there are instances when people prefer mates whose DNA is actually
more different rather than more similar.
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