We tend to think of evolution as a march through time, a climb out of the primeval ooze. In reality evolution is more like an 87 dimensional game of Snakes and Ladders (also called, as I am told by those who spent their childhood in the US of A, Chutes and Ladders). There are many directions in which you can go up and many that will take you down. One important reason for this is that the evolutionary landscape is really a stormy sea. It isn't static and it isn't wholly blind to the fate of the organism. In fact major components of the environment are evolving in concert.
We think of the environment as exerting a continuous influence resulting in evolutionary peaks, analogous to this volcano in the Andes (on the left). But the biological environment is changeable, like the clouds around the mountain.
continued at Daily Kos....
