Hans Vodder is a careful thinker, with graduate degrees from the University of St. Andrews (philosophy) and Northwest University (theology) to prove it. I met him a couple of months ago, just before I spoke at the community center in Port Townsend, Washington. Having read my book — Undeniable — Hans was instrumental in setting up that event to foster critical dialog over the book’s message.

Although we’re both people of faith, Hans favors the view that God used the evolutionary process to do his work of creating. In other words, while we agree that life is to be attributed to God, we disagree on the plausibility of the evolutionary explanation of life.

When disagreement leads to genuine dialogue, good things are bound to follow. Recognizing this, Hans and I agreed to convert our recent exchange of emails into a public discussion. We don’t know yet whether our conversation will bring us closer to agreement, but even if it doesn’t, each of us will have benefitted from understanding the other better. And we hope you will benefit as well by following the conversation.

Hans started by expressing the following concern about how I use probabilistic reasoning to argue against the standard evolutionary view:

It seems to me (Hans) that the probability distribution might make a big difference if the search has cumulative power and the search space is constrained by environmental factors. Whatever the situation was on early Earth, the specificity of certain features (geographical, climatological, chemical, etc.) would have favored certain outcomes over others: it wouldn’t have been a “level playing field” where any abstract possibility would have had just as much an opportunity for being realized as any other. In other words, might not the environment constrain the search space? If that’s right, the effective search map might be much smaller than a full-blown egg-hunt search.

How much smaller? It’s hard to say, as it seems very difficult to assign probabilistic values for historical events in general. I don’t think these considerations make the probabilistic arguments against evolution go away entirely: the odds do still seem against it. However, I remain extremely doubtful that one can assign anything like an accurate probability value to the historical circumstances under which life, if it evolved on Earth, would have emerged. From where I stand, considering the odds is a cause for caution and humility, but I think we’d be hard pressed to say whether or not a given biological event was “fantastically improbable” or merely “highly improbable.” The calculations cannot be precise enough, so far as I see, to constitute a knock-down argument against evolution.

I (Doug) answered:

I hope I can give you enough of my thinking on the probability question that we can understand each other iteratively.

Let me start by giving you an alternative to the single-sentence summary of the argument I make in Undeniable (see page 160). I could have summarized the argument this way: “Accidental explanations for life necessarily invoke unbelievable coincidences.”

To see why this has to be true, suppose I were to place a small diamond just below the surface of the sand in the Sahara Desert, and you were to set out to find it, knowing nothing other than that it’s in the Sahara. I think we can agree that the challenge for you is nearly impossible. Yes?

We come to that conclusion just by knowing how unsearchably large the Sahara is and how small the thing to be found is. We don’t have to make any assumptions about how you go about searching. Whether you devote years or decades to the diamond hunt, you can’t feasibly search more than an infinitesimal fraction of the Sahara. The fact that this one crucial resource – time — is in limited supply therefore tells us you have only an infinitesimal chance of success.

For example, if a third party (ignorant of the diamond’s location) were to impose geographical constraints on you by saying you can only look in a particular small patch of the Sahara, that wouldn’t help you at all — unless this happened to be the right patch. But for it to be the right patch would be a remarkable coincidence in itself.

The problem with all accidental explanations of life is like this, but far more extreme. You don’t need accurate measurements of probability any more than you needed an accurate measurement of the Sahara. Accuracy is only needed for judging close calls, and this isn’t a close call.

In the end, there’s no way around the fact that for any accidental causes to produce life amounts to a coincidence that’s far too extreme to be credible.

Or at least that’s how I’m thinking of it.

Editor’s note: The conversation continues on Monday.

Photo: Man searching for a diamond in the Sahara Desert, by Luca Galuzzi [CC BY-SA 2.5], via Wikimedia Commons.