WASHINGTON, July 14 (Xinhua) -- Friends who are not biologically related still tend to resemble each other when it comes to genetics, revealed a U.S. study published Monday that proved that "friends are the family you choose."
"Looking across the whole genome, we find that, on average, we are genetically similar to our friends," lead author James Fowler, professor of the University of California, San Diego, said. "We have more DNA in common with the people we pick as friends than we do with strangers in the same population."
The study, published in the U.S. journal Proceedings of the National Academy of Sciences, is based on a genome-wide analysis of nearly 1.5 million markers of gene variation from nearly 2,000 people.
On average, friends are as "related" as fourth cousins or people who share great, great, great grandparents, the researchers said. That translates to about 1 percent of our genes.
"One percent may not sound like much to the layperson," co- author Nicholas Christakis, professor of the Yale University, 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 also found that friends are most similar in genes affecting the sense of smell.
It could be, the researchers said, that our sense of smell draws us to similar environments.
It is not hard to imagine that people who like the scent of coffee, for example, hang out at cafes more and so meet and befriend each other, they said.
The opposite holds for genes controlling immunity. That is, friends are relatively more dissimilar in their genetic protection against various diseases.
The immunity finding supports what others have recently found in regards to spouses, the researchers said, adding that there is a fairly straightforward evolutionary advantage to this: having connections to people who are able to withstand different pathogens reduces interpersonal spread.
What could be the most intriguing discovery in the study is that genes that were more similar between friends seem to be evolving faster than other genes, the researchers said.
This may help to explain why human evolution appears to have speeded up over the past 30,000 years, and suggested that the social environment itself is an evolutionary force, they said.