I'm sure diversity (mutation, asexually; allele frequency shifting, for polyploid versions of the Raws) can be arranged. But I'm less sure that a sane selection criteria can be crafted. Without 'preloading' some large assumptions. That's what kills a lot of so-called-Evolution simulations.
Actually, the one I think I liked best did the latter by crowdsourcing.
Darwinian Poetry had a simple 'breeding' system (it cross-cut poems consisting of elements A1A2A3A4A5A6... and B1B2B3B4B5B6... at random intersections to create two 'children' at a time, like A1A2B3A4B5B6... and B1B2A3B4A5A6...) and left the issue of selection (comparing a random pair and upvoting one, downvoting the other, and peridiocally culling the downvoted ones before breeding a new generation to add to the survivors) down to the whims of the visitors, who could be individially capricious/random but (as a 'crowd in the cloud') produced some good developments. Or allowed them to be produced, rather.
Now, I think that with a lot of work we could get creature-Raws into a format that can allow an allele-type analogue (for similar-enough parents, though we could fulfill the half-breeds/etc of another recent request), but I fear that the additional burden of sensibly allowing diversity to thrive and then allow a sensible (game-relevent) selectivity would create a worldgen/continuation-of-history process that was far more resource intensive and just as likely to not turn out how you want it to anyway...
Right now, I don't think DF is the game for this. Randomised tropes in the setting up of various (currently) fixed elements, maybe, as is apparently highly featured in future aims, but that isn't true evolution, and true evolution (or even a half-assed mockery of it) has the potential to be more dissapointing than the proposed permutation of building blocks only at creation, and seeing where that sends History.