Life-Span Development

Life-span developmental theory provides a framework for understanding human aging. The main purpose of theory in the study of aging is to provide a context for describing and explaining the regular transformations that occur with time to representative organisms living under representative conditions. Theories in general aid the process of articulating meaningful patterns from observations that would otherwise be disconnected pieces of a puzzle and less meaningful. In the study of aging, theories serve as frameworks for organizing research findings as well as general observations or intuitions about aging and the elderly. For example, the study of aging can be seen either as largely the inevitable accumulation of deficits and losses, or as a mixture of gains and losses that depends to some extent on the individual's actions.

Aging is universal in that similar changes in human behavior occur at about the same age for all persons. Some of these age-related changes are controlled by a "biological clock," and the term, primary aging, refers to the biologically based mechanisms that are responsible for breakdowns in particular organ systems. In contrast to the consequences of many disease processes that are relatively abrupt and that affect primarily one system or organ, primary aging eventually affects all systems within the organism, and aging occurs gradually and in a cumulative fashion. For example, it is known that all sensory systems become less acute and that the speed of processing information becomes gradually slower with advancing age. Further, there are predictable changes in physiological systems and in physical appearance with aging.

Despite the ubiquity and universality of aging processes, one of the most remarkable characteristics of human aging is the wide range of heterogeneity in the expression of the consequences of aging. Secondary aging factors such as stress, trauma, exposure to toxins, and disease exacerbate the rate of primary aging. However, it is also the case that some individuals successfully avoid disease, maintain high levels of physical and cognitive function, and continue to be actively Table 1 Themes associated with a life-span approach to the study of aging. SOURCE: Author engaged in life. Individual characteristics as well as the circumstances and the sociocultural contexts associated with particular periods of historical time (e.g., the Vietnam War era) are influential in producing distinctive patterns of aging.

No one is born old, and individuals become more unique as they grow older in part because of particular histories of life experience. During the life course, the repertoire of individuals is shaped by how the person invested time and energy. The life-span approach to the study of aging is one way of conceptualizing many of the factors that affect how individuals change as they grow older, and how different individuals show different patterns of change with aging.