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For many people, friends can become a part of one's family. In a new study, researchers conducted a genome-wide analysis comparing genetic similarities between friends who were not biologically related and between strangers. The team from the University of California, San Diego (UCSD) and Yale University found that friends tend to resemble one another in terms of genetics.

"Looking across the whole genome," study co-author, James Fowler, a professor of medical genetics and political science at UCSD said according to the press release. "We find that, on average, we are genetically similar to our friends. We have more DNA in common with the people we pick as friends than we do with strangers in the same population."

Fowler, who worked with Nicholas Christakis, a professor of sociology, evolutionary biology and medicine at Yale, examined almost 1.5 million markers of gene variation. The data on 1,932 people came from the Framingham Heart Study, which provided researchers information on which participants were friends with one another. The researchers compared genetic similarities in pairs.

They found that people were more genetically similar to their unrelated friends than strangers were to one another. They calculated that unrelated friends could be viewed as related fourth cousins, which indicated that they shared about one percent of the genes. The team had accounted for ethnic backgrounds by focusing on a sample of people with "European extraction." They also looked into the people's ancestry.

"One percent may not sound like much to the layperson," Christakis said, "But to geneticists it is a significant number. And how remarkable: Most people don't even know who their fourth cousins are! Yet we are somehow, among a myriad of possibilities, managing to select as friends the people who resemble our kin."

The study was published in the Proceedings of the National Academy of Sciences.