First in the three part BBC special, RT 50:03. 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. Engineer Lloyd finds out what's missing in him. Bickering couple Liz and Craig squabble over who's the most empathic - until a stunning brain scan settles the argument. And in a television first we reveal the true effects of sex hormones on the brain by following 29-year-old Max as, under the influence of monthly testosterone injections, she turns from a woman into a man.