The process and theories of aging.

A wide variety of theories to explain the aging process have been proposed including: (1) stochastic (somatic mutation, error catastrophe, protein glycosylation); (2) developmental (immune and neuroendocrine); (3) programmed (genome-based); and (4) free radical. Although no single hypothesis fully explains all aging phenomena, the genome-based and free radical theories, in particular, are supported by significant observational and experimental evidence. In addition, these two proposals are related to each other in some respects, and possibly to other theories as well. Continued basic and clinical research in this highly complex and critically important area will add to our understanding and appreciation of the theoretical and practical implications of the aging process.