Seven-Year Friendships

When it comes to marriage, the seven year-itch is many things: a truism, a cliche, an evolutionary adaptation, a joke. When it comes to friendship, however, it is very, very real.

According to a recent study conducted by Dutch sociologist Gerald Mollenhurst, we cycle through half of our friendships every seven years. The study's larger implications upend the idea that we carefully select and solicit who we befriend. It's so random as to seem almost cruel. Your best friendship, it turns out, may owe more to convenience than commonalities. And the clock may be ticking on it.

After surveying 1,007 people between the ages of 18-65, Mollenhurst re-interviewed them seven years later, and found that despite the friendships shucked and gained, most people counted the same number of friends in their network. But only 48% of the social network remained from seven years before, and only 30 percent had the same status.

Also: We draw from a limited selection of people, making new friends under the same circumstances in which we found former friends. And we find a way, however Darwinian, to make room for them.

Or, as Audrey Hepburn said to the approaching Cary Grant in "Charade": "I'm afraid I already know a great many people. Until one of them dies I couldn't possibly meet anyone else."