Theoreticians in the 1960s who were trying to wrap their heads around the principles of why and how animals on this planet age argued that senescence is "inevitable." As time goes by, organisms grow old, and their probability of dying increases, they said.
But research into a wide range of organisms suggests this almost definitely isn't the case: there's a growing variety in how creatures grow old. On all branches of the evolutionary tree, some animals live fast and die young and those that are so old we don't even know how to measure their age.
Female sand-burrowing mayflies have about five minutes to two hours to mate before they die. Giant Sunda rats live about half a year, while the Rougheye rockfish can live over 200.
While many evolutionary principles behind this baffling discrepancy have started to surface, the molecular and biological reasons for aging — and why different animals do it at different rates — still baffles scientists daily.
