If we accept, a priori, the view that natural processes cannot be sufficient to account for our presence in the world, we've got some serious decision-making to do.
We could, for example, allow that evolution might have produced every species except for us. Even the staunchest opponents of evolution do not take this position, and for very good reason. We humans are living creatures and share nearly every aspect of our biological existence with other living things. ... There just isn't enough about us that is biologically different from other animals to say that evolution applies to them, but not to us.
We have to find another place to draw the line.
We could, if we were especially cautious, draw that line in a way that includes as much science as possible. We might, for example, accept the general picture that historical geology has given us for the age of the earth. That would put us at peace with the physical sciences. We might further agree to the general validity of the fossil record and its sweeping pattern of descent with modification. That would keep the paleontologists off our backs, and save us from repeated attack as new discoveries flesh out further detail in evolutionary history. But we would still have to find at least one essential event in the history of life to stand outside these natural processes - one thing that must have been done by the Creator. And ideally, we'd make this an event so tiny and so distant in the past history of life that no historical record of how it actually occurred could ever be found. We could, following this strategy, argue that evolution cannot account for the biochemical machinery of the living cell. That's where we could claim that a designer is required, and that's how we would protect our worldview against the ravages of evolution. Such is the viewpoint espoused by Michael Behe and others, who hold up the lofty banner of "intelligent design".
- Kenneth Miller, Finding Darwin's God, pp 59-60