Question: Why do some animals live for longer than others?

Kevin Mahon answered on 20 Jun 2012:

The evolution of lifespan is still somewhat mysterious and unknown to us, although we have some theories as to why some live longer than others – some have proposed that it is directly related to the animals size (I’m not really sure about this) but a good theory is that it is due to the animals metabolism – which is the collection of chemical reactions in the body that allow us all to live!

Small mammals are comparitively short lived compared to us and bigger mammals because they have a high metabolism, due to excessive loss of heat energy which must be replaced.

Since insects are cold blooded, they can’t control their metabolism, so their life success is wholly dependent on external temperatures. If these are favourable, the insect will live for quite a while. The most short lived insects are normally those which lack the ability to feed as adults, as evolution has designed them with dysfunctional mouths so they simply breed, then die.

Reptiles, which have an extremely slow metabolism, tend to live longer since their organs are not overworked for long periods of time.

Of course, there are other factors – importantly most of these species don’t get to live and die entirely by their metabolism, predation for example is greatly going to affect a life expectancy – if you are prey and have a fierce predator, there isa good chance you will die! Likewise disease and even more complex things like social structure (you may get eaten by your parents/sexual partner!) can all play a role!

Makes you glad to be human!