The world may never know smile emoticon I like the virus angle -
  nice twist. I can picture the little virus injection needle
  thing randomly spreading across the planet, transforming certain
  species to jump to their next equilibrium point by transforming
  their internal bacteria which then will help shape the
  development of the*bacterial symbiote species in a different
  direction. I like it better than "random cosmic rays" anyway.
  "oops, flipped a bit from 0 to 1 - time to evolve!" although
  probably more likely All sci-fi but fun sci-fi == Yeah, they
  weren't doing so great by that point. I forgot why - I thought
  it was atmospheric changes but I can't remember. Long time since
  school smile emoticon ==