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-rela ted changes in cell functions. The data support the major hypothesis t hat age-related changes are generally caused by specific physiological factors that are extrinsic to cells. The success of these manipulatio ns includes retarding or reversing specific age-related changes, and e xtending the life span. From another perspective, these findings have converted time in the analysis of senescence from an independent varia ble to a dependent variable. So far, we do not need to hypothesize any new mechanism that is not already known in disease or normal function ing.