This increase is due to improvements in sanitation, medical care, and the discovery of antibiotics. The increase in the number of older people is changing the makeup of society. There are two major theories on aging. People who follow the program theory think that aging is based on a biological timetable. Others who believe in the damage or error theory say that aging occurs as the environment assaults the body and causes it to age.
Many people believe it is a combination of biology and environment that causes aging.
Organ systems in each person can age at different rates. This slows down the body's processes and the body begins to age. The organs eventually stop working. Faulty proteins are developed and cause damage to cells, tissues, and organs. Experts used to believe that chronic disease and disability always accompanied aging.