"Humans are unique in that we create long term connections with people of our species. Not only that, we prefer the company of people we resemble," said Nicholas Christakis, a social scientist at Yale University in Connecticut.

In order to arrive at this conclusion, researchers compared gene variations between 2,000 people who were not biologically related.

After analysing almost 1.5 million markers of gene variations, they found that pairs of friends had the same level of genetic relation as people did with a fourth cousin or a great-great-great grandfather that translates into about one percent of the human genome.

"Most people do not 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," Christakis contended.

The most common gene shared by friends was the ‘olfactory’ gene involved in the sense of smell. The results suggest that choosing friends who share similar genes is a behaviour that may have contributed to human evolution.

The study appeared in the journal Proceedings of the National Academy of Sciences.

(Agencies)

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