Abstract
In 1991, the book Evolutionary Biology of Aging offered the following definition of aging: a persistent decline in the age-specific fitness components of an organism due to internal physiological deterioration (Rose, 1991). This definition has since been used by others a number of times. However, it was only a modest generalization of a definition proffered by Alex Comfort over three editions (1956–1979) of his key book The Biology of Senescence (Comfort, 1979): “a progressive increase throughout life, or after a given stadium, in the likelihood that a given individual will die, during the next succeeding unit of time, from randomly distributed causes.” The 1991 definition chiefly added reproductive fitness components to Comfort's definition, while adding the qualifiers that the fitness-component decline should be persistent and should be “due to internal physiological deterioration,” where the latter phrase was meant fairly broadly. Thus increases in mortality with age due to chronic infections such as HIV/AIDS were excluded by the 1991 definition.
Highlights
A mere definition does not necessarily tell a scientist what causally underlies the phenomenon that is so defined
Evolutionary biologists further thought that this inexorable deterioration was brought about by the progressive decline in Hamilton’s forces of natural selection (Hamilton, 1966; Rose et al, 2007)
The aforementioned 1991 book accommodated commonly inferred physiological mechanisms of aging within an overarching evolutionary framework, delineating an“evolutionary biology of aging”that subsumed conventional gerontological thinking, rejecting only those parts that were inconsistent with evolutionary theory
Summary
A mere definition does not necessarily tell a scientist what causally underlies the phenomenon that is so defined. Evolutionary biologists further thought that this inexorable deterioration was brought about by the progressive decline in Hamilton’s forces of natural selection (Hamilton, 1966; Rose et al, 2007).
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