[the_real_r2d2]

Adding some randomness could help to avoid over-fitted populations. Then you could prevent to converge to a sub-optimal state and force the system to look beyond of what it seems the best.

[bravura]

I thought mating was the main cause of genetic diversity, not mutation.

[a-priori]

Mutation introduces new alleles, and mating recombines existing alleles. Both processes increase diversity.