It is not my intention, herewith, to offer a supporting addendum to Sam Brownback’s New York Times piece about evolution, although I think his gist is surpassingly reasonable. Rather, in reading the discussion of that piece in the Corner — which I’m sure is, or might as well be, playing out in various venues across the country — it seems to me that an important point is being missed.
To begin, John Derbyshire (amidst a collection of phrases that followers of the debate will recognize as puffed feathers) offers the following explanation of his scientist response to Brownback’s scientific understanding (all emphases in original):

The problem with this position is, that you need to observe — or at least, darn it, hypothesize — some mechanism that stops the micro before it goes macro. (Not to mention that you have to posit some mechanism, other than macro-evolution, for the origin of species… But leave that aside for the moment.)
Take, for example, allopatric (“different homeland”) speciation. You have a population of living, sexually-reproducing organisms, all belonging to the same species (i.e. able to mate with each other). You observe variations within the population. You further observe, watching across several generations, that some variations (red hair, schizophrenia) are heritable in whole or part, some (appendectomy scars) are not heritable at all.
Now you divide your population in two: Population A and Population B. You separate them geographically. (Hence “diferent homelands.”) You observe that A and B have different “menus” of heritable variation (A has more redheads, B more schizophrenics). You further observe that A’s and B’s environments are different — A’s is hot and dry, B’s cool and wet.
You sit back and observe for a few thousand generations. Yep, microevolution goes on. A changes, B changes. Because they started out with different menus of heritable variations, and because environmental pressures in the two places are different, they change differently. They diverge. A thousand generations on, the two populations look and behave differently from each other. Ten thousand generations on, they look and behave way differently. Orthodox biology (“Darwinism”) says that eventually they will be so different, they can no longer interbreed. Speciation will have occurred. A and B are now two species.
Under Brownbackian evolution — micro yes, macro no — this can’t happen. They can’t go on diverging. They can only get so different, no more. The divergence must slow down and stop. But… what stops it? What’s the mechanism?

The accumulating Corner posts (here, here, here, here, here, and here) get all the way to a philosopher’s suggestion that “unless we can make a convincing case that the choice is not between relativism or dogmatism, more and more people will reject the former and embrace the latter,” but at no point does anybody address what the average person will find objectionable (even if unarticulatedly so) in Derbyshire’s explanation. How is it — why is it — that hot/dry versus cool/wet conditions ought to be expected to transform hair color and psychosis into biological differences so vast that sperm and egg will no longer function together? An equatorial African human being can still, as far as I know, mate with an Eskimo, and yet chimpanzees would be schtupped to no avail.
Now, I’m absolutely positive that there’s a very clever and ever ready response that I haven’t the time, just now, to read with the merited attention, but my experience leads me to predict that the back and forth would — not unlike the hypothesis of “micro yes, macro no” — merely change the terms of the debate, without substantially altering the beliefs of those involved. I’m not saying that those beliefs are stubbornly unreachable, but taking the discussion to the boundaries of my comprehension, I’ve always found the assumption (e.g.) that it’s just so darn logical for environmental factors to change organisms in more and more dramatic ways to dominate the details. Meaning that the details appear proposed mainly to illustrate how the assumption could be true.
To some degree, this is just how science must function. “So far, x has provided predictive information with respect to question y, and if we were able to prove that it functions also as X, then we could explain Y, or even Z.” Perhaps what’s so frustrating about the whole dispute is that rational religion functions in much the same way, just with a broader class of considerations. “Yes, but the way in which I understand 7 has a certain relevance to question y, and given millennia of compelling thought about numbers (and your certainty that X proves the whole effort to have been misdirected), I’m going to insist that there is something of 2 in Z, regardless of the alphabet.” I’m not one to disclaim science’s ability to explain the world in which we live, but to the extent that it smuggles in a philosophical materialism, one must risk accusations of creationism to state with certainty, as Brownback does, that “man was not an accident and reflects an image and likeness unique in the created order.” Simply put, there is a form of comprehension distinct from scientific thought without which no understanding of the world is complete.
Julian Baggini, the aforementioned philosopher, writes the following in the piece to which Derbyshire and Jonah Goldberg tread in their conversation:

Richard Rorty, for example, argues against Truth brilliantly, and it is far from clear that he is simply wrong. The problem is that he does not concede as unequivocally as he should that in practice his theories usually leave the world more or less as it is. Rorty believes as much as anyone else that the Holocaust happened more or less as described in history books, he just refuses to use an allegedly outmoded vocabulary of truth to say so. It is not quite fair to call his refusal in such contexts a pose, but it is certainly not quite what it seems.
Ironically, like many left-leaning intellectuals, Rorty thinks that denying objectivity and truth is politically important, as a way of liberating people from the ways of seeing the world promoted as the Truth by the powerful. However, it turns out that Rorty and his ilk seriously misjudged what happens if intellectuals deny truth stridently and frequently enough. Far from making liberal openness more attractive, such denials actually make it appear empty, repugnant and weak compared to the crystalline clarity and certainty of dogma.

Stepping back from the glint of ivory, one can see that the masses do not, in their ignorance, cling to dogma because the academics have left them no middle ground. Those academics aren’t making liberal openness seem “empty, repugnant and weak” — language that inherently buys into the academics’ elevation of power as the driving force of all human behavior — but that they make it seem wrong, or at least so unbelievable that those who profess it don’t actually behave as if it is true.
Such declarations, for all their dogmatic certainty, merely resonate all the more loudly as the bunk that they are. The more monolithic the proclamation, the more apparent it is that the intellectuals, at some point en route to their PhDs, underwent an amputation of the intrinsic human sense that that which has been created likely has a creator, that the miraculous appearance of deliberateness, joined with a longing for and feeling of purpose, is at least suggestive of deliberate purposefulness.
Too often, the purpose of denying truth appears to be the otherwise unjustified allowance of preferences that “the world promoted as the Truth by the powerful” would treat as suspect. Too often the attacks on certainty give the impression of a strategy to promote the power of those who specialize in obscurity. “You’re deluded,” they say, “in thinking that there’s any objective truth, so you should indulge my various urges and subscribe to my political solution to the world’s ills, all perpetuating a system that allows me to make a comfortable living explaining why boogers are actually lint when removed from my naval, while you toil in the fields.” They are clever enough to prance around any old Truth that might be mentioned, and they insist that the rest of us must be able to reassert those Truths in a way acceptable to them. Otherwise, we are merely retreating to the comfort of certainty, and if we begin to think that a society that devotes its resources to meaningless nonsense could use some reworking, we’re reactionary barbarians lashing out at our own insecurities.
Without drawing too close of a comparison between academics defending a philosophy and scientists defending a theory, this leads us back to suspicion of evolution. I don’t think it necessarily indicates a “new position” to which “creationists have retreated” to wonder why the burden is on believers (who often would scoff at being called creationists) to explain why humidity wouldn’t eventually make a sperm and an egg incompatible. Derbyshire does a bit of weaseling of his own when he assumes that the unlimited capacity of heritable tendencies and “environmental pressures” to change a species is so obvious that it cannot be questioned without the development of an alternative mechanism that is science-like in its exclusion of anything that is not materialistic.
Layer on enough environmental pressures, and the environment begins to look more like an oven that a wildfire, and heritable tendencies more like ingredients than random minerals. Indeed, mutations and unique natural events begin to give the impression of stirring. Thus we arrive at Brownback’s bottom line:

If belief in evolution means simply assenting to microevolution, small changes over time within a species, I am happy to say, as I have in the past, that I believe it to be true. If, on the other hand, it means assenting to an exclusively materialistic, deterministic vision of the world that holds no place for a guiding intelligence, then I reject it.

Even Goldberg argues that this sets up a “strawman… saying that if you believe in anything more than ‘microevolution’ you’re buying into a cold, godless, materialistic universe,” but that attributes more weight to Brownback’s positive argument than appears to be intended. The question that he’s answering is why he would raise his hand when asked whether he did not “believe in evolution.” His explanation is that he believes in evolution as a natural process of relatively minor differentiation, but not (as the question is often meant to imply) as a way for all life to have developed under the indifferent eye of randomness. Anything between must be specified — although the discussion is not likely to fit in an opinion column, much less a debate — so that the believer has the opportunity to specify where the proposed pressures do not appear sufficient to change the very character of the creature and where the mechanisms have begun to give the impression of design.