People have been looking for love potions since hunter-gatherer societies.

Real competition can drive up testosterone, which boosts libido.

Neither gender is routinely more jealous - although women are more willing to work to win back a lover, while men tend to flaunt their money and status and are more likely to walk out to protect their self-esteem or save face.

A hundred years ago, if you had a child out of marriage, you'd be a social disgrace. Today women feel comfortable enough economically and culturally to bring up a child without a recognized commitment from a man.

If we remained perpetually infatuated, we couldn't eat, sleep or work.

Romantic love allows you to focus mating energy. Attachment sustains that relationship as long as necessary to raise your baby.

The Internet lets women use words, which is their natural tool. Little girls speak in more complex, grammatical sentences than little boys do, and women never lose that superiority in verbal ability.