  We investigate the evolutionary dynamics of an age-structured population
under weak frequency-dependent selection. It turns out that the weak selection
is affected in a non-trivial way by the life-history trait. We can disentangle
the dynamics, based on the appearance of different time scales. These time
scales, which seem to form a universal structure in the interplay of weak
selection and life-history traits, allow us to reduce the infinite dimensional
model to a one-dimensional modified replicator equation. The modified
replicator equation is then used to investigate cooperation (the prisoner's
dilemma) by means of adaptive dynamics. We identify conditions under which age
structure is able to promote cooperation. At the end we discuss the relevance
of our findings.
