This text tells how life has evolved from the simple molecules of the primaeval soup into the complex plants and animals that now inhabit the Earth's lands and seas. Each chapter is devoted to the history of the major groups of animals - insects, reptiles, birds, mammals - and each chapter gives a history of their nature rather than a conventional natural history. The chapter on reptiles shows how they evolved from their ancestors, how they spread over the land and became the rulers of the world - the dinosaurs - and how even these massive animals fell victim to some unknown mishap, leaving the earth in turn to become populated by our ancestors, the primitive mammals.