Let's face it: in the game of life, familiarity breeds trust

People are more likely to give one another the benefit of the doubt if they have similar faces, a scientific study says.

People are more likely to give one another the benefit of the doubt if they have similar faces, a scientific study says.

The findings might also explain why youngsters tend to make friends with people who look the same and why couples often resemble one another in physical appearance.

A psychologist studying the degree to which people are prepared to put faith in total strangers has found that opponents in a game are more likely to be trusted if they share similar facial features, such as the shape of the mouth or width of the nose.

Lisa DeBruine of McMaster University in Hamilton, Ontario, said the results demonstrate a form of biological nepotism, which involves people having an innate tendency to share favours with strangers who might be distant relatives.

Her experiment involved games of bargaining between volunteers playing with an unseen opponent whose picture was displayed on a computer screen. The participants did not know the picture was sometimes a computer-generated "morph" of their own face.

As part of the game, players could choose to act selfishly by dividing a small reward equitably or to trust their opponents to divide a much bigger reward equitably.

Game theory suggests that acting selfishly should confer an advantage. But Ms DeBruine found that when the human guinea pigs unwittingly played against their own morphed image, they were much more inclined to be generous. When the same people played against opponents who did not resemble themselves, they were far more selfish and less trusting.

The guinea pigs "believed that they were playing against pictured opponents while unaware that information from their own faces had been incorporated into the 'morphed' faces of some their supposed opponents", Ms DeBruine said in a study published in the Proceedings of the Royal Society of London.

"[They] trusted opponents who resembled themselves significantly more than they trusted other opponents, but did not reward trusting moves by their opponents differentially."

One possibility is that "self-morphs are perceived as more attractive by the subjects and that more attractive people are trusted more", she said.

She ruled out the suggestion that people were merely responding favourably to familiar features because they were deemed more attractive and trustworthy. Pictures of attractive people were not trusted as much as the computer morphs, she said.

Another explanation could be that the players were merely reacting to facial features because they were familiar. However, when she used faces of famous people the participants treated them with just as much distrust as pictures of total strangers.

Ms DeBruine believes that the findings lend support to the idea of some evolutionary theorists who believe that humans, like some species of animals, are biologically programmed to identify physical traits that could indicate close genetic ties.

The study may show, she said, an innate ability to identify and favour distant family members which would have been advantageous in early human evolution when social groups were based around small bands of interrelated hunter-gatherers.

"Our human ancestors did not have mirrors until relatively recently and reflections in water would provide quite degraded information," she said.

Looking at facial features would be the most straighforward method of identifying genetic relations.

Oliver James, a clinical psychologist and author of Britain on the Couch, is not convinced that genes can explain the tendency of people to look favourably on strangers who resemble them.

"The evolutionary interpretation is impossible to prove or to disprove," he said.