Even children notice that some animals age much more rapidly than others. Their pet hamster grows frail and feeble, its sight and hearing weaken, and ultimately it dies all during the time that the pet dog is growing to be a young, vigorous adult. But the dog too will grow frail and feeble, its senses will dull, and it will die before the child born at the same time graduates from college. The comparative biology of aging uses these species differences in aging rate as an investigative tool to try to understand what mechanisms govern the rate of aging.
Animals traditionally used in the laboratory are notoriously unsuccessful at aging. Mice and rats are among the shortest lived of mammals. Consider the 2-3 year life span of a mouse to the 25-30 year life span of the similar-sized naked mole-rat or the 35-40 year life span of some bats. Ask yourself, how can a bat maintain its senses, strength, and endurance for decades while a mouse loses them in a couple of years? Comparative gerontologists have a particular interest in species like bats and naked mole-rats that age exceptionally slowly.