Men and women are just the same. Just as caring, just as promiscuous, just as good at a three point turn. Aren't they? The results of a new BBC sex survey of 500,000 people from around the globe - the largest ever carried out - provide very revealing answers. And five men and five women are put through a unique battery of experiments to uncover the real differences between the sexes.

Can science predict sexual attraction? In a ground-breaking experiment, a team of scientists orchestrate a unique speed date with a hundred singletons to test their theories - with unexpected results. The scientists analyse our speed-daters bodies, faces, and psychological and social profiles to find out what the key predictors of sexual chemistry really are.

Lyn and Alan have bickered for 21 years and are contemplating divorce. Hayley and Jay have been married for seven years, but Jay's recent affair has put their marriage under intolerable pressure. Along with starry-eyed newly weds, Steve and Donna, our warring couples go through a battery of experiments to see what's going wrong.