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Data from Wright, 1991.

Data from Wright, 1991.

maximum achievable life span (MALS), mortality rate doubling time (MRDT), and maximum life span potential (MLSP/MLP) all have very specific meanings, but like aging and senescence are not always used appropriately. Expectation of life at birth or life expectancy at birth (eo) is a demographic measure of average life span resulting from the all-cause mortality of a cohort (a group of individuals born in the same year). Expectation of life (ex) at any age (x) is a well-defined basic life table (an actuarial table based on mortality statistics that follows an entire cohort from birth to death) function. Although well defined, life expectancy data may be used misleadingly in aging research because they are based on both child and adult mortality rates and are influenced by prevailing sociocultural, political, economic, and environmental factors (Olshansky et al. 1990; Olshansky and Carnes 1994). For example, comparing eo of populations in very different cultural or ecological settings, where one group experiences high and the other low infant and child mortality, reflects sociocultural and environmental factors associated with preventable diseases and illnesses, rather than processes of senescence. However, ex calculated for ages other than birth may provide more meaningful comparisons between populations and time periods (see Table 1.1 to examine e0, e40, and e85 for the U.S. population between 1900 and 2000).

MLSP and MALS are closely related theoretical concepts commonly defined as the longest known life span or the oldest living individual of a species or the maximum predicted life span (Weiss 1981; Hoffman 1984; Harper and

Table 1.2 Estimated average and maximum life spans and ages at puberty for selected mammalian species

Life span

Table 1.2 Estimated average and maximum life spans and ages at puberty for selected mammalian species

Life span

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