The joke that married couples can appear similar may in fact be due to the tendency for couples to marry someone from a similar ancestry — whether they are aware of it or not.
That’s according to a new study published recently in PLOS Genetics.
In the first ever investigation into mating patterns across multiple generations in the United States, researchers examined genetic similarities between spouses in three generations of families.
The participants took part in the Framingham Heart Study, which has examined the heart health of residents in Framingham, Mass., since 1948.
The researchers from the University of Pennsylvania, the Boston University School of Public Health, and the University of California San Francisco found that of the 879 spouse participants, those from Northern European, Southern European, and Ashkenazi backgrounds were more likely to choose a spouse from the same ancestry.
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Seeking similar backgrounds
The researchers say choosing a partner from a similar background could be due to a number of reasons.
“Mate choice reflects a large number of factors including local geodemographics, social class, nationality, ethnicity, religion, anthropometric traits such as height and weight, as well as behavioral characteristics,” the researchers wrote.
“These patterns may also have reflected neighborhood characteristics, and the tendency for unions to occur locally.”
The study found that those from later generations were less likely to choose a spouse from the same ancestry.
“Intermixing between participants with Northwestern and Southern European ancestries was relatively uncommon in the original cohort but increased in subsequent generations,” they wrote.
This may be due to the tendency for younger generations to move around more frequently.
“While unions historically have been preferentially local, increased movements of the population over past decades are contributing to the decay of local endogamy, as seen in Framingham,” the researchers found.
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Are there health concerns?
Genetic similarity within a population is of particular significance in the area of genomic studies as it can lead to false positives in identifying gene regions associated with disease.
It can also impact estimations of the degree to which a disease may be passed on genetically.
Over several generations, the tendency for people to pick a mate from a similar ancestry has resulted in a genetic structure that has potential to bias results of genetic studies.
Professor Peter Ralph from the Institute of Ecology and Evolution at the University of Oregon, says that in small populations, genetic similarity can also have health consequences.
“In very genetically similar populations there are often increased risks of some genetic diseases, because it is effectively more likely someone gets two broken copies of some particular gene. In practice, this…