Evolution doesn't optimize for anything but the result are such that, to quote:
> The prevalent genes in a sexual population must be those that, as a mean condition, through a large number of genotypes in a large number of situations, have had the most favourable phenotypic effects for their own replication.
It optimizes for something, not in the sense of intent but in the sense that there's something that increases as evolution takes place. It's just pretty hard to describe exactly what. Darwin called it by the delightfully circular name "fitness", where evolution is the survival of the fittest and the fittest are those that survive.
(Of course, fitness is relative to an environment and the environment changes as things evolve, so it's not like there's some global 'fitness' property that increases. Just that, all else held constant, the thing which evolves tends to become better suited to reproducing in its environment.)
> The prevalent genes in a sexual population must be those that, as a mean condition, through a large number of genotypes in a large number of situations, have had the most favourable phenotypic effects for their own replication.