You share more with your friends than you think

DNA, GENES, GENETICSHave you ever marveled at just how much you and your closest friend have in common? Your interests, pleasures, the things you find funny…

Well, that connection may be closer than you think – a new study found that friends, who are not biological relatives, have more common DNA than strangers do.


The researchers, from the University of California-San Diego (USCD) and Yale University, did a genome-wide analysis of almost 1.5 million markers of variations between genes, using data from the Massachusetts-based Framingham Heart Study, Medical News Today reported. The study was chosen because it was the largest available with the detailed data on DNA required for the analysis. The study also contained information on which of the participants were friends, key in this research.

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How friends are like first cousins

Their results, published in the Proceedings of the National Academy of Sciences, compared the genetic DNA of pairs of unrelated friends among 2,000 people in the Framingham study with the DNA of strangers.

The research team, led by James Fowler of USCD and Nicholas Christakis of Yale, found that unrelated friends share 1 percent of their genes on average, which is about the same overlap of genetics expected between fourth cousins (those who share common great-great-great grandparents), Medical News Today reported. Looking at specific types of genes, the researchers found that friends share the most similarities in the genes that control the sense of smell, and are most different in the genes controlling immunity or one’s ability to protect against disease.

That number, 1 percent, is significant to geneticists, Christakis told Medical News Today. “Most people don’t even know who their fourth cousins are,” he explained. “Yet we are somehow, among a myriad of possibilities, managing to select as friends the people who resemble our kin.”

How shared DNA can keep us healthier

Sharing some DNA with our friends does offer evolutionary advantages, the researchers said. Early ancestors who had friends who had a chill at the same time they did could work together to build a fire, for example. Also, sharing a trait with others is more beneficial if people with similar genetics are around, because they’re likely to also have that same trait. Afraid of heights? You might not be fond of glass elevators in tall buildings – maybe your friend isn’t so keen on them, either.

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The findings about immunity illustrate another possible benefit of having friends with similar DNA, the researchers said – if your social pool includes people with genes protecting them against a range of diseases, everyone is better off. If you married your best friend and had children, you’ve likely passed down some good genes to help protect them from various ailments.


What is not yet known is what benefit comes from having friends who share similar genetics related to our sense of smell – or how we’re making that selection as we build relationships with people outside our own families. The finding could be an illustration of how friends often gather in the same social settings, Fowler explained, such as coffee shops.

“People who like the same smells tend to be drawn to similar environments, where they meet others with the same tendencies,” he told CBC News. However, the researchers say the underlying science behind that finding may have a more complex story to tell.

The research does promote the fact that our social ties are crucial to our health, happiness and well-being.


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