aging, in biology, cumulative changes in an organism, organ, tissue, or cell leading to a decrease in functional capacity. In humans, aging is associated with degenerative changes in the skin, bones, heart, blood vessels, lungs, nerves, and other organs and tissues. The branch of medicine that deals with the disorders of aging in humans is geriatrics.

Biologists have advanced a variety of theories to explain aging, but most of them agree that this process is largely determined by genes. This view is suggested by the great range of lifespans among different animal species—from a few days in the fruit fly to more than 100 years in some tortoises. Scientists have recently learned how to double the lifespans of such laboratory organisms as roundworms and fruit flies through genetic manipulation, and mutant genes in mice have been observed to have a comparable effect in postponing aging.

At the cellular level, an important recent finding has been that the lifespans of cells in the human body are determined by strings of DNA (genetic material) called telomeres, which are located at the ends of the chromosomes. Each time a cell divides, the telomere becomes shorter; the senescence and death of the cell is triggered when the telomere is reduced to a certain critical length. Telomerase, an enzyme that can intervene in this process, is being closely studied in relation to cancer as well as aging.

Environmental factors have been observed to affect aging as well. Scientists have discovered that they can significantly postpone aging in mice by providing them with very low-calorie diets, and recent studies of rhesus monkeys on low-calorie diets appear to be having the same results. It is believed that these diets slow the aging process by lowering the rate at which tissue-damaging substances called free radicals are produced in the body. One aim of these studies is the development of antioxidant drugs that could slow the aging process in humans by protecting against free radicals. The use of testosterone, melatonin, human growth hormone, and other hormones as "anti-aging" treatments is medically unproven and potentially dangerous, as the hormones can have damaging side effects.

See L. Hayflick, How and Why We Age (1994); J. Silvertown, The Long and the Short of It: The Science of Life Span and Aging (2013); publications of the National Institute on Aging.

The Columbia Encyclopedia, 6th ed. Copyright© 2018, The Columbia University Press.

Aging: Selected full-text books and articles

The International Handbook on Aging: Current Research and Developments By Erdman B. Palmore; Frank Whittington; Suzanne Kunkel Praeger, 2009 (3rd edition)
Rethinking Aging: Growing Old and Living Well in an Overtreated Society By Nortin M. Hadler University of North Carolina Press, 2011
The Psychology of Ageing: An Introduction By Ian Stuart-Hamilton Jessica Kingsley, 2006
The Biology of Aging: Observations and Principles By Robert Arking Oxford University Press, 2006 (3rd edition)
Cognitive Neuroscience of Aging: Linking Cognitive and Cerebral Aging By Roberto Cabeza; Lars Nyberg; Denise Park Oxford University Press, 2005
Handbook of Communication and Aging Research By Jon F. Nussbaum; Justine Coupland Lawrence Erlbaum Associates, 2004 (2nd edition)
Social Theory, Social Policy and Ageing By Carroll L. Estes; Simon Biggs; Chris Phillipson Open University Press, 2003
Behavior, Health, and Aging By Stephen B. Manuck; Richard Jennings; Bruce S. Rabin; Andrew Baum Lawrence Erlbaum Associates, 2000
Handbook on Ethical Issues in Aging By Tanya Fusco Johnson Greenwood Press, 1999
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