Explores the avenue of evolution that links natural selection and genetics - the effect of changes to the rates and timing of growth and development. McNamara delves into the living and fossil worlds to show how animals and plants have evolved when the carefully orchestrated pattern of embryological development is gently nudged off course - producing species that may have developed `beyond' their ancestors, or others that have developed less, looking more like overgrown juveniles. The author shows how this phenomenon - known as heterochrony - has affected many aspects of evolution, including the mechanism behind the selection of different breeds of animals, differences between sexes, and animal behaviour.