Aging is the process of growing old. As adults age, they become increasingly vulnerable to injury, illness, and death. Aging is a characteristic of almost all living things. The rate at which it occurs, however, varies within and across species. The biological changes associated with aging begin at the moment of conception (fertilization). In most human beings, the changes do not become visible until individuals reach 30 to 40 years of age. Age-related changes include graying or loss of hair, weakened muscles, wrinkled skin, and diminished sense of hearing and vision.
Why people age.
Early scientists and philosophers viewed aging as a natural process that removed the elderly to make room for the young. This idea suggests that the natural lifespan of an organism is fixed and determined by genetic instructions that are present at birth. However, many scientists now believe that aging is the result of various natural biological processes rather than a predetermined genetic program. Most scientists think that aging and death occur at different rates and times among individuals because of a combination of genetic variation, differences in the way people live their lives, and the random nature of the biological processes that contribute to aging.
For most organisms, the timing of death is linked to the time in the life span when reproduction occurs. The timing of puberty and menopause is particularly important. After the reproductive period, the cells, tissues, and other components of the body have accumulated so much damage that they can no longer function as well as before. This loss of function is expressed in the form of a wide range of diseases and disorders associated with aging.
How aging occurs.
Scientists do not fully understand the precise biological changes in cells, tissues, and organs that contribute to aging. One important mechanism involved in aging is the damage that accumulates in cells from unstable molecules called free radicals. These molecules are produced by natural biological processes as the body works to maintain a constant temperature and level of functioning.
The human body has many biological defense mechanisms designed to prevent or minimize free-radical damage and repair the damage that does occur. Over time, however, the damage caused by free radicals accumulates and contributes to the many processes associated with aging. Scientists are looking for ways in which they can reduce or postpone the damage caused by free radicals and possibly delay the aging process.
Overcoming aging.
Some of the effects of aging can be masked through the use of cosmetics, creams, lotions, and plastic surgery. Many people claim that vitamins, antioxidants, hormones, and various other substances have antiaging properties (see Antioxidant; Vitamin). Scientific research on these claims has yet to be completed, and most scientists doubt that the substances will work. However, scientific experiments have shown that it is possible to make some animals live longer by reducing their intake of food. Researchers are trying to understand how and why this method, called caloric restriction, works. Most scientists, however, believe that it is impossible to stop or reverse the process of aging.
