For the past year I’ve been blogging about how we can prove the theory of evolution with Bayes’ theorem plus the evidence we have available. To see all the posts on that subject, please visit the Index. In a nutshell, I’ve argued that the prior probability of evolution is at least 50% (arguably much higher), and that there are six lines of evidence (the fossil record, embryology, the ‘tree of life,’ vestigial organs, biogeography, and Endogenous retroviruses) that are almost 100% likely to exist if evolution happened, but have a less than fifty percent chance (in some cases, much less) of existing if creationism or “spontaneous generation” is true. Please see my previous posts “Ground Rules” and “Math and Tomatoes” if you need help understanding how I came up with the numbers. Anyway, let us generously assume that each line of evidence is only predicted with 90% accuracy under the theory of evolution (which is downplaying the probability quite a bit, each line of evidence arguably is predicted with over 99% accuracy). Let us also generously assume that creationism predicts each line of evidence with fifty percent accuracy, even though I have repeatedly argued that it doesn’t even predict the evidence that well. Plugging in these numbers to Bayes’ theorem, we find that evolution is over 97% likely overall (and remember, this is supposed to be an underestimate generous towards creationists, so the odds are actually much better than that!).
There are, however, two important caveats I have left out so far: is there any evidence that is better explained or predicted by creationism than by intelligent design? Creationists and IDers mostly just dispute the evidence for evolution, and I’ve tried to implicitly or explicitly take apart their contentions in my posts on the subject. However, there are two points that I know of in which they’ve tried to make a positive argument for design. The first is their claim that they “predicted” the functionality of junk DNA, which talk.origins debunks nicely and which I have debunked even further here. Their main argument, though, is that evolution cannot produce complex, functional structures. One of their primary examples is the blood clotting cascade and bacterial flagellum. The blood clotting cascade is an especially interesting example, as the research on its origins have not only shown how it could evolve step by step, but if read what we know about it closely, you’ll realize that what we’ve found out by looking at the blood clotting mechanisms of distantly related species like the lamprey has produced even more evidence of common descent! (See Kenneth Miller’s three part series on this here, here, and here). The bacterial flagellum has suffered a similar fate, as Nick Matzke has written about how it could have evolved, and Miller again takes it apart in the PBS NOVA special Judgment Day: Intelligent Design on Trial. Similar claims, like “the skunk could not have evolved” (yes, they have made this argument!) have been debunked as well, and in a very predicatable way.
The only other thing that might possibly need covering is this: I assumed from the beginning that the earth was old and that the fossil record represents a very long history of life. Questions about the age of the earth and whether the fossil record is the result of millions of years or a flood like creationists think can be answered with Roger Wiens’ article Radiometric Dating: A Christian Perspective and Stephen Jay Gould’s essay Genesis and Geology.
And that’s it! I’d love to hear from creationists and ID proponents who take the time to read this entire document: what do you guys think about this?