When married couples seem similar it’s not just because argyle sweaters were two-for-one. Researchers think it may have something to do with people’s tendency to marry spouses with the same ancestry — a move that can change the genetic structure of different populations. Up until relatively recently, people picked mates based on proximity, which meant someone from their local community and often with the same ancestors. Thanks to the Internet, folks now have the option of finding partners across the world, but a preference towards the familiar may be inherited.
The research, published in PLOS Genetics, is the first investigation of mating patterns across multiple generations within the U.S. Researchers analyzed data of three generations of 879 “white” spouse-pairs obtained Framingham Heart study — an ongoing study of the heart health of residents in Massachusetts which began in 1948. They observed those of Northern European, Southern European, and Ashkenazi ancestry chose spouses of the same background. Results also showed that these mating patterns caused spouses to be more genetically similar to each other than expected, which could change the genetic structure of populations and potentially bias the results of genetic studies.
The data also showed that this is gradually decreasing with each generation, but it still happens, Ronnie Sebro, a professor at the University of Pennsylvania and co-author of the study, told Fatherly. “Today, geography is less of a determinant affecting spouse similarity. We suspect that spouse choice may be related to cultural similarities, so individuals with similar cultures tended to intermarry.”
Sebro notes that there is no evidence that choosing a genetically similar spouse negatively affects populations — with the exception being actual inbreeding, of course. But it might change how genetics is approached in future population studies. “We suspect population genetic structure as a consequence of mating patterns and their changes over time is a general phenomenon,” he said, noting more research in the future will help determine this. Until then, blame the matching sweaters.