This book describes the experimental study of evolution and adaptation, carried out by means of combined field-work and laboratory genetics. That technique has been developed during the last forty years or so by my colleagues and myself, and by a small but increasing number of geneticists throughout the world. In discussing what has been achieved by these means many relevant pieces of work familiar to me have been omitted, while doubtless there are others that have escaped my attention. To those who have thus laboured without recognition here, I offer my apologies. Yet I would not include...