Question: How come some animals have the capability of leading far longer lives than other animals?

Kevin Arbuckle answered on 14 Mar 2014:

This is a question with lots of possible answers, and we are still very unsure which one (or combination of answers) are correct. Lots of things are related to how long a species lives including intelligence, how many children it has (and how much energy it puts into each one), body size and even toxins and other defences against predators.

One idea is that in species that are very likely to be eaten by predators or die from disease or something similar, long lifespans won’t evolve. This is because lifespan is how long it takes us to die of ‘old age’, and if an animal (or plant) almost always dies before reaching ‘old age’ then evolution has no reason to cause them to have a bigger lifespan (because they won’t reach it anyway). This seems to make sense in some cases because if you think of really long-lived animals like tortoises, trees, whales, and humans they are all good at not getting eaten by predators and things. Tortoises have tough shells, trees have tough bark, whales are too big for many things to eat them, and humans have weapons and (to stop dying from disease) medicines. So it could well be that in species that usually don’t die from ‘external’ causes (i.e. not from old age but something attacking it) then evolution acts to make them live longer.