Women are naturally prone to compete over their mates.

Real competition can drive up testosterone, which boosts libido.

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.

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.

I don’t think we’re an animal that was built to be happy; we are an animal that was built to reproduce.

Research shows that couples who have a lot of similarities, including intellectual compatibility, end up staying together.

Hair that gleams can send a clear sign that you're young and in your prime, whatever your actual age.