This unique book looks at the biology of aging from a fundamentally new perspective, one based on evolutionary theory rather than traditional concepts which emphasize molecular and cellular processes. The basis for this approach lies in the fact that natural selection, as a powerful determining force, tends to decline in importance with age. Many of the characteristics we associate with aging, the author argues, are more the result of this decline than any mechanical imperative contained within organic structures. This theory in turn yields the most fruitful avenues for seeking answers to the problem of aging, and should be recognized as the intellectual core of gerontology and the foundation for future research. The author ably surveys the vast literature on aging, presenting mathematical, experimental, and comparative findings to illustrate and support the central thesis. The result is the first complete synthesis of this vital field. Evolutionary biologists, gerontologists, and all those concerned with the science of aging will find it a stimulating, strongly argued account.