I think this discussion on ageing is interesting, but I don't really
understand why the effect of a given organism's environment has not yet been
considered. Ecologists recognize two extremes in the general approach different
organisms use in response to their environments, namely K and r strategies.
Organisms in stable, resource rich environments live longer and have fewer
offspring than those in highly unstable environments. This is the K strategy.
Sequoias and humans living in rich nations are good examples of this type. The
r strategy is something of a blitzkrieg on an environment that is only rarely
favorable. r strategy organisms have short lifespans, reproduce hugely, and eat
everything they can. An example of this is seen with certain desert shrimp that
hatch when it rains, eat and lay eggs at a ferocious rate, and die, leaving
their eggs in a "suspended state" until the next rain. Prokaryotes in general
are another example. I think differences in lifespan can be seen as the result
of natural selection pressures exerted by the environment.