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. […]

“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 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.”

Genes in common between friends are usually in areas that are changing more quickly:

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.