We're apt to fall in love with those who are mysterious and challenging to us.

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.

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.

The human brain is built to compare; it's Darwinian to consider an alternative when one presents itself.

Of all the foods we share, there is nothing more primordial than meat. It's no surprise that meat-eaters still want a partner who will give, receive and share this primordial symbol of a budding partnership.

Keep an open heart. We are wired to find love.

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.