Senescence in Natural Populations of Mammals: A Comparative Study

Here, I use published mortality data from 56 natural populations of mammals to examine evidence for senescence, an increase in the probability of mortality with age. Data on extent of senescence and life history characteristics are compared across taxa in an attempt to test theories for the evolution of senescence in natural populations. In accord with theoretical expectation, senescence is highest in short-lived species with short generation times. In contrast to theoretical expectation, however, senescent increases in mortality rate do not begin until well after age at maturity in most cases. I also present evidence in support of the hypothesis that senescence will be lower in large-brained taxa.