Joyless Moralist asks: "When did you become such an apologist for Darwin? I'm shocked!"
My position on Darwin is this. Darwin developed a very powerful concept, namely, evolution as descent with modification and natural selection, which marks an important departure in the theory of causation, applicable especially to biology but to some extent in economics as well and maybe in other fields. His mistake, which has been prevalent ever since due to man's romantic weakness for coining creation-myths, was to interpret it as a tool for discovering origins. But the Darwinian concept of descent with modification plus natural selection doesn't, strictly speaking, tell you anything at all about origins, still less that all the complexity and variety of life originated that way. Stories about origins can only be developed by combining the Darwinian mode of causation with very non-obvious, debatable, at best intuitive assumptions about the a priori probability of various potential beginning-states. When they are spun out into a comprehensive natural history, so many unwarranted (if we are to credit the reader with a high degree of philosophical maturity we can even say untenable) universal negatives must be assumed that Darwinism degenerates into mere dogmatism or myth.
The real, valid use of the Darwinian concept of causation is as a way of understanding the phenomenon of ecological equilibrium. Note first of all that ecological equilibrium is something that we actually observe in historical time, unlike evolution, of which can observe very little and only in marginal cases. Experiment can at best show the existence of Darwinian evolution, which we can deduce from logic alone, and can give us no hint of the power, versatility, creativity, etc. of this mechanism. No, the real value of Darwinism lies in the false prediction that a naive Darwinism would predict, namely, that descent with modification and natural selection should be causing constant change and biology should be in a state of flux rather than stable order. Given that descent with modification and natural selection should (be expected to) cause evolution, why do we not observe evolution in historical time, but instead, we observe species and ecosystems continuing century after century and millennium after millennium with very little change, unless they are disrupted by man? The answer to that question, the answer to which one is compelled by seriously facing that question, revolutionizes one's ideas of causation. It shows why, if the world is not simply to be in flux (as we see it is not) it must be a certain way; it must be one of a subset, large yet vanishingly small compared to the set of all conceivable biological worlds, of equilibrium ecologies in which populations and trait distributions are in a state of delicate yet stable balance.
The following world is an example of one that Darwinian reasoning might rule out. A species called the "buffalo lion" exists which, looking something like a cross between a buffalo and a lion, can eat both grass and meat, and can even tear down trees and eat wood like a termite, whch has long tunks and sharp teeth and hunts in packs, very effectively, so that it devours everything in sight, with weapons superior to the defenses of any animal. Other than that, the world looks like ours, with similar flora and fauna. A Darwinian can make an educated guess of why this world will not be observed. A species so potently all-devouring as the buffalo lion would lay waste its environment and cause an ecological catastrophe, and our flora and fauna could not survive its onslaught. The scenario could, in principle, occur briefly, but it would quickly pass away as buffalo lions drove other species to extinction.
Now, does all this "refute" Aristotelian metaphysics? On the one hand, it's true that it's not exactly clear how the scientific method, with its hypothesis and experiment, can refute a metaphysical proposition. Suppose that Aristotle says that an acorn becomes an oak because that is its telos or final cause. Suppose that we can provide a complete, experimentally supported description of why an acorn becomes an oak which relies entirely on efficient causes and makes no appeal to final causes. Is Aristotle's claim thereby refuted? I don't know. But it does seem to have been shown that it is unnecessary and unhelpful to take final causes into account to explain the acorn becoming an oak. And since telos was a scientific theory, an effort to explain the world we observe, that does seem to be a reason to abandon the concept.
One thing I've never been able to understand about final cause is: How can one speak of a cause proceeding from the future (final = end) to the past? Surely causation, like time, is one-directional, going only from past to future and not vice versa! But maybe final cause can be consistent with the idea that causes must precede effects if the final cause, as a goal or purpose, pre-existed the effect. And that is easy enough to understand if we're talking about a human being with a plan or purpose: the human being conceives the plan first, then engages in actions to bring it about. Aristotle sees purposes at work in biology too: a rabbit's long ears have the purpose (i.e. telos, final cause) of hearing predators. Observation gave abundant reason to think this way; as indeed does casual language. But how can the "purpose" of a rabbit's ears be the same sort of thing, metaphysically, as a "purpose" conceived in a human mind as a motive for action? In what mind does the purpose reside (for it certainly does not reside in the rabbit's!)? It might sound appealing to a partisan of Christianity to say "God," but that is a false move, for we know what "purposes" are from our human experience, and this does not give us the right to extend the concept or purpose to God. And if He does have purposes, our access to knowing them is limited at best. If one is forced to ask foolish questions like, "Why does God, when equipping rabbits with long ears, value the rabbit's safety over the wolf's supper? Why does God exhibit the opposite preference when designing the wolf's fangs?", it is a sign one is on the wrong track.
A concept of evolutionary causation dispenses with the need for any concept of "purpose" in biology as something basic or fundamentally causal. To say that the purpose of an acorn is to become an oak comes to seem merely poetic, even anthropomorphic, as if an acorn wants to become an oak in the way a boy might want to become a priest. To create a concept of telos by conflating human purposes with "purpose" as exhibited in the way animals and plants are adapted to their environment then appears to be a mere mistake.