Until recently, we regarded love as supernatural. We were willing to study the brain chemistry of fear and depression and anger but not love.

Your sweetheart calls you by another's name. His eyes linger too long on your best friend. He talks with excitement about a girl at work. And the fire catches. Jealousy - that sickening combination of possessiveness, suspicion, rage, and humiliation - can overtake your mind and threaten your very core as you contemplate your rival.

Romantic love is an obsession. It possesses you. You lose your sense of self. You can’t stop thinking about another human being.

It certainly would have been adaptive for ancestral man to have a chubby wife during stressful times of famine. Not only would she have had more calories to burn, and thus more energy and endurance, but since fat stores estrogen, she would have remained fertile for longer.

Whether you're married or not, relationships - and the satisfaction tied to them - are extremely important for increasing men's and women's quality of life.

Anthropologists have found evidence of romantic love in 170 societies. They've never found a society that did not have it.

When you're in the throes of this romantic love, it's overwhelming - you're out of control, you're irrational, you're going to the gym at 6 A.M. every day - Why? Because she's there.