While aging is familiar to all of us, exactly how it occurs on a molecular basis has been an area of intense study and interest. We take it for granted that different species age at different rates, yet we do not have a good understanding of why and how. Most mammals have similar numbers of genes, many of which show conserved function, yet there are several orders of magnitude differences in lifespan across mammals. For instance, mice and small animals live shorter lifespans, yet other animals such as bats, naked mole rats, whales, elephants and primates age significantly slower.