DNA tests prove your close friends are probably distant relatives

You can choose your friends, but you can't choose your family, or so says the adage. But scientists have found that by choosing friends we may also be unwittingly choosing the company of distant relatives.

A study into the genetic nature of friendship has found that, on average, close friends are likely to be as genetically related to one another as fourth cousins who share the same great, great, great grandparents.

The findings suggest there is an unexplained mechanism that helps us to choose our friends based on how similar they are to us in terms of their DNA, said James Fowler, professor of medical genetics at the University of California, San Diego.

"Looking across the whole genome 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," Prof Fowler said.

The phenomenon may have arisen as part of an evolutionary process, he said.

"The first mutant to speak needed someone else to speak to. The ability is useless if there's no-one who shares it," he said.

"These types of traits in people are a kind of social network effect." The research involved genome-wide studies of nearly 2,000 people who were part of a larger, long-term investigation into the factors that influence heart disease and who, as a result, had already had their DNA analysed for the smallest mutations. Prof Fowler and his colleague Nicholas Christakis of Yale University took pairs of individuals based simply on whether they were friends or total strangers and analysed their DNA to see how different or similar each member of a pair was to one another.

- The Independent