If two very different people pool their DNA, they'll create more genetic variety, and their young will come to the job of parenting with a wider array of skills.

Romantic love is an addiction.

There's magic to love... Millions of years ago we evolved three basic drives: the sex love, romantic love, and attachment to a long-term partner. These circuits are deeply embedded in the human brian. They're going to survive as long as our species survive on what Shakespeare called, this "mortal coil."

From my studies of genetics and neuroscience I have come to believe that people fall into four broad personality types - each influenced by a different brain chemical: I call them the Explorer, Builder, Director, and Negotiator.

Both sexes like the exercise and challenge of sports, but for men it's also a basic display behavior for impressing and winning a mate.

You can get into a very fancy car and know everything about the engine, but when you drive in that car, you feel that rush. In the same way, I think the more you know about love, the more you can enjoy it. And knowing about your personality type, who you are and what kind of person you're dealing with gives you a great leg up.

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.