Largely undirected rant warning!
There's one annoying thing that often comes along with a fair number evolution discussions out there: Why do things evolve and why do things evolve?
The former has a fairly simple short answer (PZ and friends are more qualified to give the long answer): Critters come up with new genes, traits, and so forth (mutation, etcetera), and some of them help produce more offspring (natural selection). Because the critters with the 'good' genes reproduce more, those genes become more common. The process continues over several changes in what makes a gene 'good'.
The latter, as far as we can tell, has no answer: Things evolve because that's how the process goes on. There's no 'big' answer to 'why'. There's no end goal to evolution, just like there's no end goal to gravity. Despite what the comic books tell you, there's no drive towards a 'perfect' being. One annoyance I had during a Voyager episode involved a race of dinosaur-descended 'aliens': To confirm the origin of the dino-aliens, Captain Janewry and The Doctor (did they ever get that guy a name?) went into the holodeck and at one point asked the computer "If the hadrosaurus had continued to evolve, what would it evolve into?" and the computer responded by making a dino-alien hologram. I would think that calculating the evolution of a species would require extensive description of the circumstances.
And don't get me started on "Threshold." I erased that extra-painful episode from memory up until Agony Booth reminded me.
I think (based on gut feelings at the moment, so feel free to dismiss them) this straw man version of evolution grew from religious concepts like 'the great chain of being' and efforts to claim that evolution put man on a exalted pedestal as the ultimate being (despite contradictory claims that evolution says we're 'merely' animals), instead of god. Sorry. Humans are really nifty, but the universe didn't assign any special treatment to them, unlike gods, who seem to have humans first and foremost on their minds, almost as if they were designed to stroke our egos half the time (and crush them the other half: Deities often seem to be schizophrenic or something). Seems that humility is equally as sinful as arrogance to Creationists, except when they commit them. (I doubt they do much of the former, though)