Every one of us possesses an armoury of instincts which keep us alive. We are often barely aware of them, but they act every day to protect us from danger and keep us fit and healthy. Babies alter the pitch and volume of their screams depending on how urgently they need help. In the first programme of the Human Instinct series we explore how this most basic of instincts means we're all born to survive. A Baby's Cry Within a few hours of birth, many animals are not only feeding but standing up and walking around. By comparison human babies are virtually useless. So the most important weapon in a baby's survival armoury is an astounding scream. It can reach 97 decibels - equivalent to a pneumatic drill. Babies alter both the pitch and volume depending on how urgent their need of help. The louder and more piercing the scream the quicker the response. With this simple tactic a human baby ensures it gets all it needs - attention, loving care and of course food. A Question of Taste Without food we die. But can our instinct to eat explain why we all crave fatty, often unhealthy, food? Like all our instincts, our appetites were formed millions of years ago. In this uncertain world, laying down fat was the perfect way to ensure against times when food was scarce. Robert Winston inspects a human parasitic roundworm. Our ancestors who craved food which was high in calories and rich in fat lived and passed on their genes to their children - those who didn't, died and left no descendents. Gradually, over millions of years, that craving for calories became instinctive behaviour. But there's an even more sophisticated side to our craving for food. We also instinctively know what is safe to eat and what is not. Our tongue has evolved to have 5,000 taste buds - letting us know what to swallow, and what to spit out. And we also have an instinctive reaction to things which could give us a disease or make us sick. At the London School of Hygiene an