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 More than you may think.
People tend to choose spouses who have similar DNA, according to
scientists who reported on Monday the results of a study exploring
the genetic resemblance of married couples.
The researchers examined the genetic blueprints of 825 U.S. married
couples and found a significant preference for a spouse with DNA
similarities across the entire human genome.
The study compared this affinity for husbands or wives with similar
DNA makeup to the well-established and strong tendency of people to
marry mates with similar educational levels. The researchers found
that the preference for a genetically similar spouse was about a
third as strong as the preference for a spouse with comparable
education.
The 1,650 people studied in the research were non-Hispanic, white
men and women born between the 1930s and 1950s who were taking part
in a broader U.S. government-funded study involving health and
retirement.
 "We do know in some sense that people prefer genetically similar
spouses because we know that people tend to date and marry within
their own racial and ethnic groups. We worked really hard in this
study to not just replicate that fact," said researcher Benjamin
Domingue of the University of Colorado's Institute of Behavioral
Science, who led the study.
"We eliminated racial variability and tried to control for ethnic
variability. And we still find a preference for genetically similar
individuals," Domingue added.
The researchers measured genetic similarity by comparing 1.7 million
individual DNA building blocks, known as single nucleotide
polymorphisms, in the study participants. They compared the genetic
makeup of the married couples to other randomly chosen people of the
opposite sex in the same pool of study participants.
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Domingue said the actual mechanism for a person being drawn to
another person's genetic similarities is probably complicated and
multifaceted - "just a whole host of things," he noted.
The researchers noted that people usually pick spouses with similar
backgrounds and characteristics in addition to education, including
race, religion, age, income and body type. Genetic similarity can be
added to the list, they said.
"For example, people clearly care about height in picking partners.
To the extent that tall people marry other tall people, that is
going to result in genetic similarity among spouses. But it is
difficult to know whether height or genes is driving this decision,"
Domingue said.
The researchers said it would be interesting to see the results of
similar studies involving other populations including additional
races, interracial spouses and gay couples.
(Reporting by Will Dunham, editing by G Crosse)
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