What a nice little generator concept!
However I cannot help myself to provide some suggestions as well.
You could rewrite some sentences to fit-in two more prompts. This is my attempt that does not change the mechanics at all, only adds climate change and passage of time.
One player is Time, the others are Species.
Species: describe yourselves.
Time decides:
- One species lives unchanged
- One evolves
- Rest extinct
Pass the Time role to next player.
Million years passes.
Climate changes.
Repeat twelve times.
Feel free to adapt.