This book discusses the controversial issue of whether animals are designed according to the same rules that engineers use in building machines, namely that materials and energy are used economically while attempting to achieve a high level of performance. There is considerable scientific controversy surrounding this question because, although there is much evidence suggesting that animals are indeed well designed, evolutionary biology tells us that animals are not engineered but result from evolution by natural selection. In this volume these highly controversial questions are debated by eminent experts on the basis of a wealth of evidence ranging from the molecular biology and biochemistry of enzyme systems through the study of bone and muscle to the design and function of integrated systems of energy supply and the nervous system. The authors have made a special effort to present the chapters in a form that is accessible to a broad readership of biologists interested in basic principles.