Similarity is key to romance or friendship and is hard-wired into our brains, a study found.
It could lead to a fundamental change in understanding affairs of the heart – and also sounds a warning for the idea that couples can change each other over time.
Psychologists looked at romantic couples, friends and acquaintances.
They found, contrary to popular belief, partners are already alike at the outset.
Professor Angela Bahns, of Wellesley College, Massachusetts, said: “Picture two strangers striking up a conversation on a plane, or a couple on a blind date.
“From the very first moments of awkward banter, how similar the two people are is immediately and powerfully playing a role in future interactions.
“Will they connect? Or walk away? Those early recognitions of similarity are really consequential in that decision.”
Researcher Chris Crandall, of the University of Kansas, in the US, said: “You try to create a social world where you are comfortable, where you succeed, where you have people you trust and with whom you can cooperate to meet your goals. “To create this, similarity is very useful.”
The research is published in the Journal Of Personality And Social Psychology.