Biology of Aging

The study of the biology of aging, or biogerontology, has as its primary objective understanding the basic processes that underlie aging and agerelated disease. For some this means increasing human life span, for others it means increasing human health-span. In either case, the ultimate objective is to reduce human suffering. Whether one wishes to extend human life span or alleviate age-related disease, understanding the underlying processes of aging is essential. Aging is not simply the result of the passage of time. Think of the life spans of guppies, dogs, horses, and humans. All age at a regular rate, but the rate of aging is vastly different from one species to another. Is aging different in each species, or does the same set of processes run at different speeds in different species? What do we actually mean by aging? The simplest definition is the loss of homeostatic ability with the passage of time. Homeostatic ability is the ability to maintain internal stability. That is, the ability of an organism to maintain a stable internal environment in the face of environmental challenges such as changes in temperature, humidity, air quality, and so on. At the most basic level, the loss of this ability is the primary deficit of aging.

What most of us think of as aging, however, is the loss of teeth, hair, muscle strength, memory, and reproductive ability, as well as the accumulation of wrinkles, joint pain, and what are commonly called the infirmities of old age. These changes are age related, but are not aging itself. They are not the inevitable consequence of aging, but rather the often-observed accompaniments of aging. The concept of "normal aging" is used to try to distinguish between aging as a process or set of processes, from aging as the result of the accumulation of damage from environmental insult, the ravages of disease, and the wear and tear of living. Normal aging is assumed to mean the age changes that result from basic biological processes. Whether normal aging actually can be studied is a matter of some controversy, although most gerontologists believe that the concept is meaningful.

The details of normal versus disease-related (or pathological) aging are the grist for biological theories of aging. These theories are attempts to explain the data we observe as we study aging organisms of many species and to construct frameworks that relate these explanations to a basic understanding of what aging means. Some of these theories assume that aging processes are not the same as wear and tear or the consequence of disease, while others assume that aging is essentially the result of these factors. The major biological theories of aging are described in a separate entry on theories.

Other approaches to the study of aging look at age-related diseases directly (geriatric medicine), at the aging of populations and incidence of age-related diseases in these populations (demography and epidemiology), and at the social and behavioral changes that characterize aging (social gerontology and gerontological psychology).