Unlike most lab animals, bats are excellent models for understanding human senescence and
ageing and to discover the means to improve health into old age. Although there are some merits
to mechanistic hypotheses of ageing (e.g., that life span should be inversely related to metabolic
rates, as the latter contribute to the accumulation of intracellular debris leading to ageing), the
bestsupported theory of ageing is evolutionary and linked to life history (41). According to this
theory, if adults in a population experience high extrinsic mortality (e.g., from predation),
natural selection will favor short-term reproductive success over long-term survival and
maintenance, resulting in rapid senescence after reproduction, past the age at which most
individuals would have died in a natural population . The survivorship and life history of
house mice reflect this pattern, with intrinsic mortality and morbidity rising sharply past
one year of age, even under highly favorable lab conditions. Conversely, populations with low
extrinsic mortality will experience continued selection throughout longer lifetimes, favoring
slow senescence and resulting in longer, healthier lifetimes. Because bats are both nocturnal
and capable of active flight, they have escaped the attention of most predators. This in turn
has led them to evolve the relatively unusual vertebrate combination of long life spans with small
bodies. As long-lived mammals, in some cases living >41 years, bats offer clues regarding the
mechanisms for maintaining high function across internal systems over a long life span, longer
than any similar-sized mouse can live. Natural selection over millions of generations for continued
health and reproduction throughout a long lifetime has equipped bats with excellent cellular and
system-wide mechanisms of maintenance. This is particularly impressive considering that the high
metabolic rates characteristic of bats are expected to produce reactive oxygen species, typically
causing chronic inflammation and hastening senescence (46). However, the maintenance of function
alone is not enough, as cells and tissues need constant repair over the course of a multiyear life
span. Studies focused on bats have identified suites of cellular repair mechanisms that potentially
evolved to support the unusual longevity of bats. These genes and variants can be readily compared
with human genes to discover specific features that would enable a healthy old age.