Substance first, style later. Darwin proposed a "reasonable hypothesis" to account for the pattern of similarities that naturalists had discerned among living things: Common structures, especially when they are apparently constraints on the organism's ability to adapt to its environment, indicate descent from a common ancestor. What's the alternative? A whimsical or a sadistic Creator?
Far from "hardening into a dogma," what happened in subsequent research is that more and more evidence showed up in support of common ancestry. As we engage in our antiquated debate, molecular biologists are sequencing genomes and discovering just how much of the residues of the DNA of organisms past survives in organisms present. As more of the data become publicly available, I hope that the Kansas students will tap into the appropriate sites on the Web and see the evidence for themselves.
Johnson's latest alludes to the fossil record, so perhaps he's gearing up for a final salvo on the notorious "gaps." As many Darwinians have noted, the fossil record shows some fine-grained transitions, for example the evolution of mammals from reptiles. In Darwin on Trial, Johnson obfuscates this issue by pointing out that there are debates about just which mammals are ancestral to which. It's fair enough to recognize those debates, but one should recognize the central point: There's no doubt that all these organisms (some mammals, some reptiles), are related, but the tricky part is telling the daughters from the sisters and the cousins and the aunts.
Of course, there are lots of transitions that are less well documented. Fossilization is a chancy business and one can't simply demand that intermediates should be found. Johnson presumably believes that there was a continuous sequence of sacred texts extending from the last decades of the first century to the editions of the Gospels we have today. But I could challenge him with the "gappiness" of the text record. He'd reasonably reply that the ancient world was an insecure place, that cities were pillaged, libraries burned, and so forth. Just so. Equally, the processes of geological formation make the chances that organisms will survive as fossils extremely low. We should be thankful that enough survives to show the kinds of intermediate forms that Darwinians hypothesize.
There's a lovely example from entomology. E.O. Wilson and some of his colleagues once predicted what the ant ancestor would look like. There's very little chance of preserving an ant, but one form did turn up in some amber. It was strikingly close to the predicted form.
The evidence for the relatedness of living things is just overwhelming. So, how do they get modified? Johnson pooh-poohs "natural selection" on the grounds of some ill-defined information explosion. But we can observe the operation of natural selection on laboratory populations of organisms, most dramatically in microorganisms. What's the problem in thinking that complex organisms, particularly at times of changing environments, might not have acquired favorable mutations, even mutations that modified their patterns of development, giving rise to new forms? Absolutely none. Our increasing molecular knowledge will help us to understand how this works, and may well enrich and revise contemporary understandings of natural selection, but, even before we have the details, there's no reason for thinking that natural selection doesn't do on a large scale what we can see on a small scale.
The analogy with stuttering radios is misleading. Johnson ought to know enough about genetics to appreciate that mutations typically modify DNA by deletion, insertion, or base change. Those modifications may result in an altered form of a protein. The altered form may make different reactions possible. The different reactions may make a developmental process go slower or faster. And that may result in a new trait--occasionally even a beneficial trait. But, as I noted from the beginning of our discussion, until we have a firm grasp of the molecular details, our claims about the modes of operation of natural selection should be tentative.
The children of Kansas ought to be told that. They should also be given the evidence for the age of the earth, and shown the evidence for common descent. They should learn what natural selection has been observed to do, and how contemporary Darwinian biology extrapolates from it. They should not be left in the dark because some people want to make the classrooms safe for doctrines that thoughtful religious people abandoned a century ago.
A last note on tone. Unlike some of my friends (who are convinced that creos make up the rules as they go along), I think anti-Darwinian arguments should be answered. But nobody ought to pretend that this is a serious, ponderous, academic debate. Hence I prefer some light-hearted raillery ("creo" for example, is good Australian banter). The ideal would be to emulate Monty Python, and nail creationism to its perch. I apologize for falling short.