should not be confused with geriatrics, which is a field of medicine that studying the treatment of existing disease in aging people, rather than the treatment of aging itself. There are numerous theories of aging, and no one theory has been entirely accepted. At their extremes, the wide spectrum of aging theories can be categorized into programmed theories - which imply that aging follows a biological timetable, and error theories - which suggest aging occurs due to cumulative damage experienced by organisms. Stochastic theories Stochastic theories of aging are theories suggesting that aging is caused by small changes in the body over time and the body's failure to restore the system and mend the damages to the body. Cells and tissues are injured due to the accumulation of damage over time resulting in the diminished functioning of organs. The notion of accumulated damage was first introduced in 1882 by biologist Dr. August Weismann as the "wear and tear" theory. Wear and tear theories Wear and tear theories of aging began to be introduced yet in 19th century. They suggest that as an individual ages, body parts such as cells and organs wear out from continued use. Wearing of the body can be attributable to internal or external causes that eventually lead to an accumulation of insults which surpasses the capacity for repair. Due to these internal and external insults, cells lose their ability to regenerate, which ultimately leads to mechanical and chemical exhaustion. Some insults include chemicals in the air, food, or smoke. Other insults may be things such as viruses, trauma, free radicals, cross-linking, and high body temperature. Accumulation Accumulation theories of aging suggest that aging is bodily decline that results from an accumulation of elements, whether introduced to the body from the environment or resulting from cell metabolism. Mutation accumulation theory Mutation accumulation theory was first proposed by Peter Medawar in 1952 as an evolutionary explanation for biological ageing and the associated decline in fitness that accompanies it. The theory explains that, in the case where harmful mutations are only expressed later in life, when reproduction has ceased and future survival is increasingly unlikely, then these mutations are likely to be unknowingly passed on to future generations. In this situation the force of natural selection will be weak, and so insufficient to consistently eliminate these mutations. Medawar posited that over time these mutations would accumulate due to genetic