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A new lover will cost you two friends

Finding a new lover may cost you two close friends. A new boyfriend takes up so much of a woman's time, and consumes so much of her energy, that she is often too tired to invest in her platonic relationships, new research claims.

The research, led by Robin Dunbar, head of the Institute of Cognitive and Evolutionary Anthropology at Oxford University, found that men and women are equally likely to lose their closest friends when they fall in love.

Previous research by Dunbar found that people typically have five very close friendships -- that is, people they can turn to if they are in emotional or financial trouble. So how does a new relationship typically affect our attachment to old and dear friends?

The study, published in the journal Personal Relationships, investigates how people trade off spending time with one person over another when their lifestyle changes as a result of a new relationship. It found connections with family and close friends suffer when people start a new romance.

Dunbar said: "If you go into a romantic relationship, it costs you two friends. Those who have romantic relationships, instead of having the typical five 'core set' of relationships only have four. And of those, one is the new person who's come into their life."

The study used an internet questionnaire to quiz 428 women and 112 men about their relationships. In total, 363 of the participants had romantic partners.

Dunbar said, "If you don't see people, your emotional engagement with them drops off and does so quickly. What I suspect is that your attention is so wholly focused on the romantic partner you don't get to see the other folks you had a lot to do with before, and so some of those relationships start to deteriorate."

In a complementary study, Dunbar looked at how men and women maintain friendships on the social networking website Facebook.

Women's Facebook friends are usually friends from their everyday life. Whereas men tend to collect as many friends as they can, even if they hardly know them.

"Boys seem to be in a competition to see who can have the most Facebook friends and that could be a form of mate advertising.

"One of the cues women use for male quality as a mate is the number of other girls chasing them, so signing up lots of girls as Facebook friends seems to be a good idea," Dunbar said.