Other people have coverred the probability arguments against evolution, already, but I'd like to cover it from the viewpoint of an aerospace engineer. Specifically, while reading this essay, I read the line, "The numbers just don’t match up — the universe would have to be much, much older than it is for random mutations to have produced that variety of life that we see on earth," with a link to this article.
I compare these types of arguments to the one that says bees can't fly. Most people have probably heard this before, but to explain it to those that haven't, if you take standard aerodynamic theory and do a rough back of the envelope calculation applying it to a bee, you could come up with the conclusion that bee's can't fly. For the size of their wings, and the speed that they move them at, the theory predicts a lift that would actually be less than the weight of the bee.
I'll be honest, I've never actually gone through this calculation. What's the point, when you know that bees can fly, and I'm not really concerned with designing bees, anyway. But supposing I did go through with the calculation and it did predict that bees couldn't fly, would it then make sense to say that, indeed, bees can't fly? Of course not. Observation tells us that bees fly - the error would be somewhere in my theory or calculations (applying steady state, high Reynolds number aerodynamics to a non-steady state, low Reynolds number application, for those interested), but that's exactly what these probability arguments are. Evolution has occured. There's enough evidence that it's not really a question. If you have a theory that says that evolution couldn't have occurred, either you've made a mistake in your calculations or assumptions, there's a problem with your theory, or perhaps, bees can't really fly, after all.
