The Science of 'I Love You'

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Playboys who want short-term flings like hearing declarations of love before sex.
Corbis

THE GIST

- Most people think that women are the first to say, "I love you" in relationships, but men most often say it first.

- Women and men who value long-term relationships are happier to hear "I love you" after sex than before.

- Playboys who want short-term flings like hearing declarations of love before sex more than afterwards.

For many relationships, there is a single moment that marks a major turning point toward either a future of togetherness or one that splits into separate roads. And that moment usually involves three little words: "I love you."

In books and movies, this simple sentence may seem full of mystery and romance. But a new study suggests that science and evolution may help explain who, in the real world, declares love first and how each partner feels when he or she hears it. Many of the results defy stereotypes.

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Even though most people think that women are the romantics in a relationship, for example, men most often say "I love you" first. And most people are happier to hear those words after having sex with their partners than before -- except, that is, for playboys on the prowl for short-term hookups, who prefer to hear it beforehand.

To explain their results, the researchers invoke a time when sex inevitably meant the possibility of pregnancy. It would make sense, in that context, for women to be more cautious about expressing love and more skeptical of declarations about a man's feelings for them.

If those instincts persist in the modern age of birth control, the findings may also offer advice for singles navigating today's dating scene.

"If somebody is saying 'I love you' before sex happens, it probably does pay to be a little more skeptical about it," said Josh Ackerman, a social psychologist at the MIT Sloan School of Management in Cambridge, Mass.

"There are all of these underlying factors that go into this kind of thing that we think is very amorphous and can't be quantified, which is love," he added. "In fact, there are these very specific forces on the willingness to say love and how you feel when people say 'I love you.'"

Social psychologists have long known that men tend to express love first in relationships, even though public perception is just the opposite, and the new project started by confirming those assumptions.