People who develop relationships with one another are already similar at the outset, study finds

Selecting friends and partners similar to ourselves is so common that experts describe process as a 'psychological default'

Professor Bahns said the findings could be seen as a "cautionary message" (Getty Images)

It’s often said that birds of a feather flock together – now scientists are arguing they have the evidence to back up this claim. People who go on to develop friendships or romantic relationships with each other are already similar at the outset of their social connection, and their personalities, attitudes and values are unlikely to change much over time, a major study on friendship formation has suggested.

Selecting friends and partners similar to ourselves is so common that experts in the US described the process as a “psychological default”, putting paid to the notion that opposites attract.

From the very first moment two people meet, their similarities play a “powerful” role in dictating the likelihood of future interactions, according to the study from researchers at Wellesley College, in Massachusetts, and the University of Kansas.

"You try to create a social world where you're comfortable, where you succeed, where you have people you can trust and with whom you can cooperate to meet your goals," said one of the paper’s authors, Chris Crandall, professor of psychology at the university of Kansas. "To create this, similarity is very useful, and people are attracted to it most of the time."

“Selecting similar others as relationship partners is extremely common – so common and so widespread on so many dimensions that it could be described as a psychological default," said co-author, Angela Bahns, assistant professor of psychology at Wellesley College.

Friends with dissimilar points of view did not necessarily influence each other over time, according to the study, published in the Journal of Personality and Social Psychology.

Professor Bahns said these findings could be seen as a "cautionary message" for people who believe they can persuade their friends or romantic partners to come around to their way of thinking. "Change is difficult and unlikely; it's easier to select people who are compatible with your needs and goals from the beginning," she said.

The researchers noted the drive toward similarity can lead to benefits such as "stability of identity, value systems, and ideology” but that “limited exposure to different ideas and beliefs” can be a major drawback.