SHAPES OF TIME. The Evolution of Growth and Development.

Have you ever wondered how evolution produced the wing of a bat, the foot of the first amphibian, the tiny arms of the Tyrannosaurus, or the eye and brain that allow you to read these words? Conventional wisdom would say natural selection. But can this alone explain the subtle nuances and wonders of evolution?

Shapes of Time explores evolution down another, much neglected avenue that links natural selection and genetics -- the effect of changes to the rates and timing of growth and development. Kenneth J. 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.

McNamara 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 behavior. Heterochrony accounts for the "Peter Pan syndrome," in which some species look like their ancestors' children. It explains what was really behind the evolution of flightless birds, how the dinosaurs got so big, how pterosaurs managed to produce a wing supported only by their fourth fingers, and what has driven the evolution of the animal closest to our hearts -- the largest primate species with the biggest brain and longest childhood -- Homo sapiens.

Kenneth J. McNamara is senior curator of invertebrate paleontology at the Western Australian Museum in Perth. He has investigated the role of heterochrony in evolution in a wide range of living and fossil animals in Europe, Australia, China, and Africa. He is co-author of Heterochrony: The Evolution of Ontogeny.