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

Women have a better sense of smell than men do, and it's even sharper in the middle of their menstrual cycle, when estrogen levels peak and women are more likely to be deciding whether a man's attractive.

In general, men are wired to notice obvious signs that convey interest in mating - a warm smile, for example - and ignore other subtleties, like if your lipstick is faded.

Psychologists maintain that the dizzy feeling of intense romantic love lasts only about 18 months to-at best-three years

Men tend to be hierarchical, but women are driven to make lateral connections so they can cooperate.

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.

I can't conceive of caring more about my president than my own partner.