This book, part of a series from The Open University in the United Kingdom, is about animal behaviour. The behaviour of animals, including humans, is very diverse and often very complex. Studying behaviour draws on the work of scientists from several disciplines, including ethologists, psychologists, physiologists and biochemists. The question that most of them are interested in answering is: why does an animal behave in the way it does? The possible answers - development, survival value, evolutionary history or cause-and-effect - are the themes that run through this introduction to behaviour and evolution.