In this edition, he reveals that our instincts are honed to survive in a world far riskier than the one we inhabit today, and that this is why we often crave food high in calories, reject food that could be poisonous, and react to primeval dangers such as snakes.

In this last programme, Professor Robert Winston discovers why we do so much for friends and family, and will even risk our lives for complete strangers, often on split-second instinct.

Professor Robert Winston examines human instincts and patterns of behaviour. He explores the drive to succeed, looking at how different chemicals are released into the brain when we win or lose, and learning about the impact of being a younger sibling on behaviour patterns.

Professor Robert Winston explores the complex world of sexual attraction, investigating why men are more open to casual sex, what drives women to be unfaithful and what can ignite male sexual jealousy.