One further discussion point is whether evolution is or is not purposeful (teleology). - Evolution certainly looks purposeful in the sense that it continuously changes toward the more complex. Complexity does not guarantee survivability, the key to natural selection. Gould in 'Full House' defends this by first pointing out that the only direction for random mutations is away from bacteria (one-celled animals or plants) to something more complex. (My feeling is why should bacteria became more complex; they have been successful as they are for 3.6 billion years? That supports the idea there is a drive to complexity in the evolutionary process.) For randomness Gould points out the 'drunkard's walk' and 'random walk' math to match random mutation. This certainly supports all the various banches of evolution in plants and animals. But the drunk has a purpose. He is trying to get home, and the odds are with him to a degree that he will get to his front door. - But if one looks at a diagram of random walk, the path can circle around, back up on itself. To me evolution doesn't seem to do that. How often are branches found that circle back to become less complex? - So I am not sure that Gould has really clearly removed teleology from evolution. I hope our resident math expert, Matt, would comment.