Last night I watched a couple of episodes of Morphed, the Nat Geo program that follows the evolution of one line of animals (dinosaur to turkey; land mammal to whale). The narrator has a gorgeous rich voice and sounds just like Worf's brother (but is not). Anyway, as a former biology major I love this kind of thing. The land mammal-to-whale story took millions of years but in Song of Scarabaeus I found a way to speed up "evolution" - quote marks used because it doesn't work the same way as normal evolution at all. It might be called "guided evolution".
And not guided in the sense of animal breeders creating new kinds of dogs through selective breeding. In Song, evolution occurs when tailor-made retroviruses alter the genes of plants and animals to change the organisms during their lifetimes. (These changes are also passed on to offspring.) This usually takes place on planets with very primitive life, organisms with short reproductive cycles, so an entire ecosystem can get a facelift in a few months or years.
The objective is to create an ecosystem suitable for human life - removing the toxins, balancing the oxygen and carbon dioxide in the atmosphere, creating topsoil and nitrogen-fixing bacteria, and so on. At least, that's when things go right.
When things go wrong, anything can happen... anything my imagination can dream up!