Paul Orwin (via Charles Murtaugh) has an interesting post on the cosmological argument for God's existence:

Well, I always find it a bit humorous how people with intense mathematical training can blithely state something like "the chance of human beings arising from Evolution are infinitesimal" or "the chance of all of these physical constants being just so, allowing for us to exist, is very small". Any time someone invokes an argument of this type, they are making a serious logical error. How many times have the physical constants of the universe been set? How many times has life on Earth evolved (ok, there can be some debate on this one, given the history of cosmic catastrophe on the earth's surface)? The answer, in both cases, is once. Not to put too fine a point on it, but you simply can't argue "What are the odds?" about something that has only, and can only, happen once! It is simply not a useful discussion.

Well why not? Orwin doesn't explain. Let's take a non-controversial example: The chances that I, as an individual, would be born. Here I am -- I was indeed born, and that was something that could only happen once. Does that really mean that it is meaningless to ask, "What were the odds that the individual Stuart Buck would ever exist"? It might be difficult to measure the odds -- you would have to estimate odds for my parents' meeting, for their mating at the exact moment that would produce me, and so on for all my ancestors. But the mere fact that I could only be born once is irrelevant, isn't it?