One branch of investigation into the mechanisms and progression of aging uses comparisons between species of differing longevity as a way to identify where to work. The ultimate aim is to narrow down the exact biological differences between short-lived and long-lived species, a process that can probably be simplified by focusing first on the exceptional cases.
Surveys and theorizing of the sort quoted below are a part of the process of deciding which of the thousands of readily available species to study are most likely to yield useful information:
Maximum lifespan in birds and mammals varies strongly with body mass such that large species tend to live longer than smaller species. However, many species live far longer than expected given their body mass. This may reflect interspecific variation in extrinsic mortality, as life-history theory predicts investment in long-term survival is under positive selection when extrinsic mortality is reduced. Here, we investigate how multiple ecological and mode-of-life traits that should reduce extrinsic mortality (including volancy (flight capability), activity period, foraging environment and fossoriality), simultaneously influence lifespan across endotherms.
Using novel phylogenetic comparative analyses and to our knowledge, the most species analysed to date (n = 1368), we show that, over and above the effect of body mass, the most important factor enabling longer lifespan is the ability to fly. Within volant species, lifespan depended upon when (day, night, dusk or dawn), but not where (in the air, in trees or on the ground), species are active. However, the opposite was true for non-volant species, where lifespan correlated positively with both arboreality and fossoriality. Our results highlight that when studying the molecular basis behind cellular processes such as those underlying lifespan, it is important to consider the ecological selection pressures that shaped them over evolutionary time.
Those of you following along over the past decade or so as researchers picked out exceptional species in order to investigate the details of their biochemistry will not be too surprised to see flight linked with longevity. Bats and birds feature prominently in the lists of species with unusual longevity for their size, and there are a range of theories as to how the metabolic demands of flight might lead to the evolution of a longer-lived species.