It seems to be a law of nature that order does arise from chaos. In fact, I might propose that it is one of only two things I can think of right now that really are laws of nature,** in the sense of universal truths that we see ordering creation. Both of them are strangely linked to scale. One of them is the law of non-contradiction, which applies with iron force at levels above the quantum, but seems subject to looseness in the absence of observers at the smaller levels. The other is that irreducibly probabilistic features at this smaller level prove to give rise to remarkable order at the highest scales.
But let's start with the objection. One of the things that 'everybody knows' about evolution (and the closely allied theory of natural selection) is that Darwin is the starting point for it. This well known fact, however, is not at all true. The theory that the vast profusion of strange forms in nature arose accidentally over time is one that Aristotle argues against in the Physics II, in a context that makes it clear that it was popularly held among some Greek thinkers. Let's look at the argument, because it's actually a pretty plausible one. He is arguing that Nature acts for a cause, and he treats the counterargument:
A difficulty presents itself: why should not nature work, not for the sake of something, nor because it is better so, but just as the sky rains, not in order to make the corn grow, but of necessity? What is drawn up must cool, and what has been cooled must become water and descend, the result of this being that the corn grows. Similarly if a man's crop is spoiled on the threshing-floor, the rain did not fall for the sake of this-in order that the crop might be spoiled-but that result just followed. Why then should it not be the same with the parts in nature, e.g. that our teeth should come up of necessity-the front teeth sharp, fitted for tearing, the molars broad and useful for grinding down the food-since they did not arise for this end, but it was merely a coincident result; and so with all other parts in which we suppose that there is purpose? Wherever then all the parts came about just what they would have been if they had come be for an end, such things survived, being organized spontaneously in a fitting way; whereas those which grew otherwise perished and continue to perish, as Empedocles says his 'man-faced ox-progeny' did.This argument should make clear that our modern deniers of evolutionary theory -- though many of them do not know it -- are inheritors of Aristotle's view. This is not a surprise, since most of them are devout Christians, and Aristotle's view was brought into the Catholic doctrine before the Reformation.
Such are the arguments (and others of the kind) which may cause difficulty on this point. Yet it is impossible that this should be the true view. For teeth and all other natural things either invariably or normally come about in a given way; but of not one of the results of chance or spontaneity is this true.
Still, we now know that Aristotle is just wrong about this, right? That's the point we started with. Things that come about by chance do exhibit extraordinary order, at least when viewed at the proper scale. Far from being evidence of purpose in Nature, this is simply a law of nature. Wait, what? Read that again: why should a purposeless nature have laws? Because it does, that's all, goes the argument. We observe them, and we aren't going to deny the plain evidence of our eyes.
There is another problem, though, which is that evolutionary theorists still need purpose in nature. It is, in fact, their explanations of this sort that strike us as least plausible -- but they are indispensable. Observe:
Once upon a time, there was an ape that stood up. Why it stood up nobody knows, but once upright it found it could use its hands to fashion tools from sticks and stones. So it stayed standing up. And once it decided to stay standing up, its brain started to grow. Why its brain started to grow nobody knows, but with a bigger brain the ape, which was by now an ape-man, could make better tools and even speak. Why it started to speak nobody knows. And by then it wasn’t an ape-man any more, but a human. And those humans with the most developed brains – Homo sapiens – used their cunning to spread throughout the world. All the many other kinds of human and ape-man died. Why they died nobody knows. When the Homo sapiens were lords of all, some of them became curious about where they had come from. Having a poor collective memory, they at first thought the world had simply been handed to them by a god who happened to look just like they did. But a few began using their inflated brains to try to piece together a story about how it had all begun with an ape that had once stood up....This is the very problem Aristotle was pointing out as a proof that this kind of explanation could not be correct. His example is your teeth: your mouth is very well ordered for the kind of food you need to eat. Things that happen randomly do not give rise to such perfect order: it would be like a rockslide just happening to give rise to a perfectly-formed house, and not once, but over and over. If we observed such rockslides making houses for men, we would have to say that there was some reason for it -- something informing the process that was directed at house-building.
There remains something about the evolutionary account of our origins that sounds a little like a just-so story.
Evolutionary theory argues that there is something directing the process: survival. Most of the random mutations prove not to be any good, and are discarded via the simple means of death. Some of them are -- so the theory goes -- and by providing an evolutionary advantage, they are sometimes retained and forwarded. At the proper scale, it ends up looking like excellent design, but the only purpose directing the order was survival.
But this is inadequate, and not merely for the reasons that our feminist readers keep mentioning (i.e., that most of these arguments for why a given natural quality is 'advantageous' could just as easily be built out the other way). It's not just that the explanations read like 'just so stories' that are demonstrably inadequate. It's also that we see similar patters of order arising from chaos in things that are inorganic, and not at all motivated by survival.
That suggests that there is something else at work -- something that (if we view the scale in a way that favors the large scale) appears to be an ordering principle in Nature itself. It could be a unifying principle that explains the rise of life, as well as why the survival principle falls in so nicely with the inorganic ordering principles. That's just what Aristotle was talking about, and it's what our modern Christian objectors see also.
Alternatively, it could prove to be multiple causes that happen to align in effect. In any case, we ought not to shove aside the objection as meaningless or empty. There is a problem there, and it's based on a very old argument with a very respectable pedigree. I think it deserves to be considered more carefully, even if its principle proponents don't always quite know why they object as they do.
* Why "chaos" when there seems to be some level of order, i.e., probabilistic order? I'm using the term to indicate where even orderly behavior is nevertheless irreducibly contaminated with randomness: the best we can do is to provide a waveform of possibilities, but any of these can be realized. As D. M. Armstrong points out, a probabilistic "law" permits even the most improbable outcome -- in theory, in fact, it does so infinitely, so that every single case ordered by the law could turn out to be the most improbable outcome. That's a pretty chaotic kind of law!
** One might argue for things like the Second Law of Thermodynamics or the law of gravity, but these cases are more problematic than they appear. In addition to a certain odd paradox of observations, a law that implies increasing order on higher levels of scale is not necessarily compatible with the Second Law; it may be that the appearance of increasing entropy is related to the scale of observations. In terms of gravity, the proponents of the Higgs field argue that it is not a law of nature, but a function of the existence of the Higgs Boson, which particle physicists think they have demonstrated. If that is the case, gravity arose shortly after the Big Bang, and is not a product of "Nature" on the grand scale, except insofar as nature is permeated by the Higgs field.
Of course, much of this is quite speculative physics. I don't take a firm position on any of it, because my training is in philosophy and history; there is always more to learn.