life cycles

[french at RUST.ZSO.DEC.COM]

For many organisms, a pre-programmed life-cycle
appears to dominate other components of ageing such as
damage from radicals and radiation.  For example, trout
turn ugly just before spawning and die shortly afterwards.

It seems unlikely that a trout's DNA suddenly deteriorates
from radical and radiation damage unless a repair mechanism
is turned off near the end of its life cycle.

Has anyone estimated the relative importance of DNA damage versus 
life-cycle in humans as a cause of death?  Are we close to the 
maximum possible life span allowed by our DNA repair mechanisms?