<P> Most living species have at least one upper limit on the number of times the cells of a member can divide . This is called the Hayflick limit, although number of cell divisions does not strictly control lifespan . </P> <P> 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 . </P> <P> 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 . </P> <P> The longest - living person whose dates of birth and death were verified to the modern norms of Guinness World Records and the Gerontology Research Group was Jeanne Calment (1875 - 1997), a French woman who lived to 122 . Reduction of infant mortality has accounted for most of the increased average life span longevity, but since the 1960s mortality rates among those over 80 years have decreased by about 1.5% per year . "The progress being made in lengthening lifespans and postponing senescence is entirely due to medical and public - health efforts, rising standards of living, better education, healthier nutrition and more salubrious lifestyles ." Animal studies suggest that further lengthening of human lifespan could be achieved through "calorie restriction mimetic" drugs or by directly reducing food consumption . Although calorie restriction has not been proven to extend the maximum human life span, as of 2014, results in ongoing primate studies have demonstrated that the assumptions derived from rodents are valid in primates as well (Reference: Nature 1 April 2014). </P>

The average length of life of members of a species is called