Introduction

Denckla and Bolla have postulated an aging hormone produced by the pituitary-thyroid system. Probably the most long-standing dichotomy of views about aging is between the "extrinsic" or "epi-phenomenal" theory and the "intrinsic", programmatic, or "biochronometer" theory. While this widely accepted theory may furnish an evolutionary frame-work for the study of aging, so far it has offered few clues about physiological or biochemical mechanisms. Gerontology, in the effort to gain the knowledge that will enable everyone to continue in active good health throughout the entire life span, is very much in the position of medicine before the germ theory of diseases was established. A further impediment to nutritional research, especially in relation to aging, is the apparent fact that there is no certain theory, not even an agreed-upon, most likely hypothesis, about the nature of the timing mechanism or mechanisms which set the pace for aging.