Studies of the evolution of plants and animals have focused on the dual role of genetics and natural selection. How a genetic mutation actually produces the variations in shape and size of an organism has, up until now, not been fully addressed. Recent studies have shown that relative changes in the rates and timing of growth during ontogeny, known as heterochrony, play a significant, and much underrated, role in evolution. This book presents an overview of current research in this field. Perspectives covered include molecular biology, cell biology, palaeontology, macroevolution, speciation, ecology, sexual selection and behaviour in both extinct and living organisms.