Robert Winston hosts this exploration of the automatic reflexes that keep humans alive without their noticing, from the flinch at a sudden loud noise to the surge of disgust at spoiled food. The film moves through staged experiments and field observation to test how much of everyday behavior is hard-wired rather than chosen: volunteers are put through fear triggers, attraction and mate-choice scenarios, and situations designed to provoke aggression or cooperation, while researchers explain the evolutionary pressures that built each response. Winston connects lab results to real survival stories, using them to argue that instincts shaped for a much older environment still fire inside modern life, sometimes helpfully and sometimes not. The tone stays plain and demonstrative, letting the experiments carry the argument rather than dramatic narration. By tracking instinct through fear, disgust, attraction, and social bonding in turn, the film builds a picture of a species still largely run by machinery it rarely notices operating underneath conscious decisions.