Comment by Ben10 on Life's Story Continues · 2008-11-22T01:31:57.000Z · LW · GW

Evolution is optimizing fitness as defined by the ability to survive and replicate in the organism's environment.

During periods of great change in the environment, we see great changes in the fossil record. So often, evolution "speeds up" and "slows down" for no other reason than the underlying region changed (not just environmental region, but search region). After environment change, there may be new low hanging fruit (once again, in search space, not just actual fruits).