Physical Changes in Late Adulthood
Aging brings about physiological changes. Or put another way, people get old. There are two dominant theories of aging:
1. The genetic preprogramming theory of aging holds that human cells have built-in "self-destruct" mechanisms. In fact, however, programmed cell death (called apoptosis) happens throughout the life cycle. The cells of the body are replaced on a regular basis; old cells die as new cells are born. Presumably, however, if this theory is correct, the body is also preprogrammed to shut down the cell replacement process after some period of time. (In princi- ple, under ideal conditions, human physiology should be self-sustaining up to the age of 120.)
2. The wear-and-tear theory simply maintains that the mechanical functions of the body work less efficiently as years go by. Joints creak and give out. Muscles wear out. Digestive processes work less well. In short, our bodies, like that of a used Chevy, are good for only a limited number of miles.
Cognitive Changes in Later Adulthood
The cognitive effects of aging vary, but they aren't very pro- nounced. The brain doesn't shrink, for example, and while memory may not work quite as well as it did, the capacity for abstract and creative thought may actually increase. Many successful novelists are over the age of 50. The idea that the mind remains active throughout the life cycle recently has received scientific support. You'll recall the concept of neurogenesis, the finding that cerebral neurons continue to develop even as we age. Of course, there's also evidence that people either use it or lose it. Being mentally active goes along with successful thinking and high levels of creativity, like those found among many artists and active intellectuals.
The Social World of Later Adulthood
According to the disengagement theory of aging, people gradually withdraw from the world-physically, socially, and psychologically.
Withdrawal permits more time for reflection, and decreased emotional investment in relationships, after all, must end in death.
By contrast, the activity theory of aging maintains that people who age successfully keep up the active life and social rela- tionships of middle adulthood. Instead of withdrawing, one keeps on keeping on. However, it seems that either keeping it going or withdrawing will accompany a process of life review. We examine and evaluate our lives, maybe a bit like a film critic.