Friends Found To Be Genetically More Similar Than Strangers
July 15, 2014

Friends Found To Be Genetically More Similar Than Strangers

Brett Smith for - Your Universe Online

If you’ve ever thought of your circle of friends as a second family, you may be on to something as a new study has found that on a population-wide level friends are more closely related to each other than strangers.

Published in the in the Proceedings of the National Academy of Sciences, the study indicated that friends who are not biologically related, may be similar to each other genetically.

"Looking across the whole genome," said study author James Fowler, a professor of medical genetics at the University of California - San Diego, "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."

The new research is based on data from the Massachusetts-based Framingham Heart Study – which contains both detailed genetic data and information on participants’ friendships. The study team started by identifying over 1,900 unique participants and examined pairs of unrelated friends against pairs of unrelated strangers. The same people, who are neither family nor romantic partners, were used within both kinds of samples. The only difference was their social relationship.

The researchers found that friends are about as "related" as people who share great-great-great grandparents, also known as fourth cousins. This is the equivalency of about one percent of our genes.

"One percent may not sound like much to the layperson, but to geneticists it is a significant number,” said study author Nicholas Christakis, professor of sociology, evolutionary biology, and medicine at Yale. “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 looked at specific sets of genes and found friends are most comparable in genes affecting the sense of smell. The contrary holds for genetic protections against disease, which makes sense the researchers said. They pointed out that having different immunities around you reduces the chances of interpersonal spread.

The researchers also developed a "friendship score” as part of their research to predict who will be friends at around the same level of assurance that scientists currently have for using genetics to predict a person’s chances of obesity or schizophrenia.

The study team pointed out that there are numerous advantages to having a friend with a genetic resemblance, such as having the same instincts or abilities for a particular situation.

"The first mutant to speak needed someone else to speak to,” Fowler said. “The ability is useless if there's no one who shares it. These types of traits in people are a kind of social network effect."

Finally, the researchers noted genes that were very similar between friends seem to be evolving quicker than other genes. They said this may explain why human evolution appears to have accelerated over the last 30,000 years, and they indicate that the social ecosystem itself is an evolutionary drive.

“It seems that our fitness depends not only on our own genetic constitutions, but also on the genetic constitutions of our friends,” Christakis said.


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