December 12, 2008

Theistic evolution

John Wilkins, blogger, philosopher of biology, and agnostic, has a post up on theistic evolution -- the view that natural selection (`Darwinism') and theism are compatible, because God can (somehow) use the mechanisms of natural selection to achieve God's ends, whatever those happen to be. Wilkins' argument is that theistic evolution, in order to be based on natural selection as biologists actually understand it, must include some rather stringent criteria that have some strong theological implications. In particular, he argues against a view he calls interventionist evolutionism, on which God is actively involved as a proximate efficient cause of at least some part of the process of natural selection. The alternative view -- which he doesn't name, but we can call non-interventionist evolutionism -- has God involved only insofar as God chooses to create a world in which random events turn out in such a way that the natural laws lead to the realisation of God's ends.

That will probably make sense only if you know a fair bit about how natural selection works and have read Augustine on free will. So, imagine natural selection as an extremely complicated progressive betting dice game. Every round, the dice are rolled, and your payoff (or loss) depends on the number showing and how you and the other players have done in the last few rounds. The interventionist God fixes the dice and makes players bet certain ways on every single round, while the non-interventionist God chooses the players (based on their betting habits) and loaded dice before the game starts, and then steps backs and lets things run of their own accord.

Wilkins' argument that interventionism `establishes a limitation to science, and is indistinguishable from special creation' and that, on the interventionist view, `to be a theist is necessarily to give up some of the explanatory power of science in favour of a providential account (which we cannot know anyway, because God's Ways are Mysterious)'. The idea seems to be that the interventionist God amounts to a supernatural black-box, into which natural science can never peer, and hence can never explain in full detail how an organism came to have this or that feature. Meanwhile, secular biology (and non-interventionism) can give these sorts of full-detail explanations, at least in principle, and so interventionism comes with the price of not being able to do everything secular biology (and non-interventionism) can do.

Those of you who were at UPS with me might remember a similar argument against creationism and intelligent design. (Yes, I know I made some pretty ridiculous claims in that paper. I was young, give me a break.) I still think this argument (suitably rewritten) is a strong one against creationism and intelligent design. But I don't think it's strong against interventionism. Wilkins is playing a double standard here, requiring the interventionist to give explanations that are very different from those of secular biology itself.

Let's consider how a creationist, an interventionist, and a secular biologist would all explain the evolution of the human eye. The creationist claims that God simply created humans, eyes and all, in one fell swoop. This is, as per my old paper, a completely unexplanatory `explanation'. God simply acts, and we can go into no further detail. The secular biologist gives us an elaborate structural narrative, describing the different structures of the human eye, the order in which they developed, and the selection pressures that lead them to have the features they do.

Such an explanation leaves open a lot of details for further research, while still being satisfying at a certain level. It does better, in both respects, than the creationist account. However, it does not offer an account of the history of the eye that can even hope to be accurate down to the last detail. What we will never get in this explanation is an account of the causal factors of the point-mutations in the DNA of our ancestors. Even if paleontology could give us the DNA of every single animal that was an ancestor of contemporary humanity, the causes of the genetic differences between those animals (errant high-energy photons, for example, or some virus) are lost forever. To go back to the gambling example, even if we knew the rules by which the gamblers bet and the result of every single dice roll, we could never hope to explain why the dice came up with the result they did. We will never get what we might call a complete causal history, either of the dice game or the human eye. While we can hope to get a structural explanation of incredible detail, we cannot hope to get a causal explanation.

Finally, note that the interventionist God is involved only at the causal level, not the structural level. Like rigging the dice on every round to get a specific result, this God fiddles with the DNA of creatures at the level of point-mutations. Hence, the interventionist can still hope to give a structural explanation at exactly the same level of detail as the secular biologist; similarly, her theological commitments imply that her hopes of giving a causal explanation break down at the same level of detail as those of the secular biologist, albeit for different (or additional) reasons.

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