EVERY time you fall in love, it costs you two close friends, according to British research out today that suggests the human capacity for intimate relationships is strictly limited.

While adults boast an average of six people in their inner circle of intimates, when they form a romantic attachment this drops to five, one of whom is their new partner, a study led by Professor Robin Dunbar, of the University of Oxford, has suggested.

This means that two people who were once counted as best friends are demoted to the second rank, he said.

"We have just shown that if you have a romantic relationship, it actually costs you two friends," said Professor Dunbar, who is director of Oxford's Institute of Cognitive and Evolutionary Anthropology.

Love's damaging impact on friendship, however, does not apply when somebody starts an affair while keeping up a long-term relationship.

"Some people in the study had formed a secondary relationship too, and we asked whether that also cuts your friends down but it doesn't," Professor Dunbar said.



"When we looked at the data, it turned out that the legal partner no longer belongs to the inner circle."

Professor Dunbar told the British Science Festival in Birmingham that while he has yet to explain the results fully, he believes they reflect the way in which the all-consuming nature of a new romance leaves less time for other close friends and crowds them out.

"We have quite literally only just discovered that, and it was a bit of a surprise. Probably the reason is that intimacy correlates very tightly with frequency of interaction, and I think what's happening is that is destabilised.

"If you don't see someone, your emotional engagement with them drops off with time. What I suspect happens is your attention is so wholly focused on your romantic partner that you just don't get to see friends you had a lot to do with before."

Previous research has shown that most people have about five or six very close friends - those they see daily, or to whom they would turn in a crisis - though women generally have slightly more than men.

People generally have another 12 to 15 very good friends, who they see at least once a month or whose death would cause them great distress.

There is then a wider friendship circle of about 50 people, and a more extended social group of about 150 people who a person knows well.



The figure of 150 is sometimes known as "Dunbar's number" - the maximum number of people with whom one can sustain meaningful social relationships - which matches the typical size of hunter-gatherer communities.

Originally published as Falling in love 'costs you two mates'