Which physical features light the flames of passion when we see a stranger across a crowded room? And why do women's faces subtly change over the course of every month?
What makes you sexy and attractive to the opposite sex?
Everyday, attraction starts the same way for millions of people around the world with a glance.
But which physical features light the flames of passion when we see a stranger across a crowded room? The signs of beauty turn out to be the same the world over and were biologically programmed to spot them. And its all because beauty is the bait we use to attract a mate.
Surprisingly, the very first impression we make on other people often has nothing to do with our faces or our figures. Its the way we move.
Good movers are sexy because they come across as fit, healthy and co-ordinated. And that means theyre likely to have good genes. Just what you want in a partner with whom you might start a family.
When it comes to beautiful faces we reveal that symmetry is the key. To prove this theory leading experts at the University of St Andrew's in Scotland analyse the faces of two models, Hannah and Jason.
Incredibly, experiments at the University of Newcastle in England have found women's faces become more symmetrical and attractive to men when they're ovulating.
Its a bombshell revealing that, like many animals, human females can become more desirable to males when they're ready to conceive.
And a woman's monthly cycle has another trick to play. It can change her taste in men. While ovulating she may find more masculine looking partners attractive, possibly because their features are associated with strong genes.
What about the future of beauty? As we make huge advances in genetic engineering and cosmetic surgery were gaining the power to completely transform the way we look.
More and more people may use this knowledge to push the rules of attraction to extremes. Fantasy will become reality - some women could even end up looking like Lara Croft
Whatever happens in the future, the best way to make a big first impression will remain the same: just smile.
Storyteller produce and distribute documentaries and factual programming specialising in animals and nature; from endangered species and what's being done to save them to mysterious animal and monster stories.