FRAR course on laboratory approaches to aging. Theories of aging.

This review of gerontological theory cites diverse examples of neural and endocrine involvement in the senescence of mammals and some other multicellular species that suggest fundamental involvement in age-related changes in cell functions. The data support the major hypothesis that age-related changes are generally caused by specific physiological factors that are extrinsic to cells. The success of these manipulations includes retarding or reversing specific age-related changes, and extending the life span. From another perspective, these findings have converted time in the analysis of senescence from an independent variable to a dependent variable. So far, we do not need to hypothesize any new mechanism that is not already known in disease or normal functioning.