Vox has, by his own accounts, been trying to fight off illness, so he's rather graciously refrained from posting until I could finish up. (rueful grin) And I intend to finish up, after this post. In the meantime, Vox, hope you have a speedy recovery.

First of all, I’d like to note some points of agreement with Vox, lest any be led astray:

"I have no alternative to offer TENS subscribers at this point in time, nor do I think I am likely to in the future, but Scott's juxtaposition of my position with Kepler's regarding the Ptolemic model----no doubt made with tongue firmly in cheek---is correct in the sense that there is no reason for scientists to abandon TENS at this point in time. It is, as he and others have said, the best model they've got right now, and it's a perfectly reasonable thing to continue to use it to look for ancient bear-whales and fruit flies that can't breed with other fruit flies."

I admire Vox’s candor, and his pluck. In a zero-sum game, this concession could be beat like a drum, constantly reminding him of his failure to provide another model, much less evidence for that model. I’ll pass, in favor of treating his conclusion:

"I don't object to that, but I'm not particularly interested in it either. Let me know when you're ready to test it instead of using it as a historical dowsing device."

Well, I’m ready to test it and I’m going to demonstrate such a test in the next post in this series, but first honesty requires me to acknowledge a conceptual muddle.

At one level, I know that TENS has been tested, and that this is the best scientific explanation for life’s diversity—as Vox conceded. Strictly speaking, TENS is a theory about the dominant role of natural selection in driving evolution. There are factors other than natural selection known to lead to evolution (such as genetic drift), so TENS is not held dogmatically in individual cases in the absence of data; it's simply the hypothesis of first resort. But, happily for us Darwinians, when individual cases are examined, we typically (but not always) find clear evidence that evolution has occurred, even to the point of leading to a new species, and that natural selection of some kind is involved.

The muddle emerges, however, not in the test of nature (which TENS itself passes with flying colors!), but when TENS is taken to serve as the explanatory framework of modern biology, the ‘big idea’ that unites all sorts of observations from different research programs. There is always the possibility that forces or agents other than natural selection could’ve been involved in individual cases, and so if we are going to start inferring that the large-scale changes we see in the fossil record are the sum of countless individual acts of selection which are themselves impossible to verify, we can sympathize with Vox’s skepticism. I’m even willing to give him the benefit of the doubt for his claim that this skepticism predates and is independent of his conversion to Christianity.

Ideally, what we would want is a method of independently confirming that the morphological changes we see in the fossil record are actually the result of changes in the genetic makeup of the population, and clear evidence that these changes support an inference of common descent between different species. Happily, with the emerging science of genomics, we can do just that with many large-scale events. In my next post, I’m going to choose precisely such an example, one that creationists will feel compelled to admit that, if true, must be one of the large-scale events, and an illustration of the ‘macroevolution’ so many of them are so keen to deny.

As a sneak preview, consider the magazine cover above.

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