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maximum life span
Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death. The term can also denote an estimate of the maximum amount of time that a member of a given species could survive between life and death, provided circumstances that are optimal to their longevity.
Most living species have at least one upper limit on the number of times cells can divide. This is called the Hayflick limit, although number of cell divisions does not strictly control lifespan (non-dividing cells and dividing cells lived over 122 years in the oldest known human).
==Definition==
In animal studies, maximum span is often taken to be the mean life span of the most long-lived 10% of a given cohort. By another definition, however, maximum life span corresponds to the age at which the oldest known member of a species or experimental group has died. Calculation of the maximum life span in the latter sense depends upon initial sample size.
''Maximum life span'' contrasts with ''mean life span (average life span'', ''life expectancy)'', and ''longevity''. Mean life span varies with susceptibility to disease, accident, suicide and homicide, whereas maximum life span is determined by "rate of aging". Longevity refers only to the characteristics of the especially long lived members of a population, such as infirmities as they age or ''compression of morbidity'', and not the specific life span of an individual.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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