Ed Feser has a helpful discussion on the way that, in Aristotelianism-Thomism, efficient causes can both be real, and subject to God as teleological first cause. In this way, the concept of evolution can be perfectly compatible with the God of Chriostianity who disposes all things according to his will.
A big part of his reasoning is to draw the distinction between the intrinsic nature of something, and its fashioning into an artifact. One example he gives is the liana vine that by nature grows through the tree canopy so that Tarzan can swing on it, and the hammock Tarzan makes from it, which derives only from the artifice of the man. Its “hammockness” is an accident of the vine rather than a result of its nature.
Feser goes on to repeat (and unpack) his disagreement with Intelligent Design, the big problem being that if God “imposes” on, say, living matter, something that turns the reptile into a bird, then the bird is not a creature with its own nature, but a mere artifact. That argument has some force from a number of points of view. However, it necessarily implies that in evolution the reptile, within its own nature, has the potential to become a bird, which is not a great problem if God created it thus.
At one level, the question being begged is whether the reptile indeed has that capacity in its nature, or more generally whether the capacity for evolution is a part of life – and beyond that, perhaps, a capacity of nature. For the whole question of first and efficient causes depends on the sufficiency of the latter. In classic Thomism, one assumes that the nature of a reptile has no potential to become that of a bird, which is why they remain separate species in experience. Thomas, no doubt, was happy to assume God created them separately, without stumbling over their being in some way mere artifacts. So Feser’s position depends on our discovering something new about the nature of reptiles, and the whole of reality, whether that be just the propensity of organisms to generate random mutations and be subject to natural selection, or an entirely new realm of physics by which complex natures emerge from simple ones. That, of course, is the factual controversy over Darwinism and Feser’s philosophical position does nothing to solve it.
But what I have said above also raises doubts for me over how valid the rest of his argument is. If, as Thomas probably believed, God created natures separately rather than by evolution, then the question of artifacts is a separate one. The limiting case is the original creation, which we can take to be the Big Bang for discussion purposes. At that point, we assume, God created the entire Universe, perhaps with all its potential to diversify and evolve, from nothing. In other words, there was, at the start, no “natural” efficient cause, and God simply imposed its existence upon it.
Does that, then, make the Universe a mere artifact – like Feser’s intelligently-designed reptile upgrade? Clearly not, for he created it with a real (Universal) nature to do all that it does and will do. But if, in Aquinas’ time, one wondered about the six day Genesis creation, one would simply say that God imparted new kinds of nature to each new kind of object. The fact that he caused the earth to bring forth vegetation does not necessitate evolution by natural efficient causes, but allows for God’s imposition of a new form on existing matter to create a true vegetable nature.
Or one could look at the creative miracles of Jesus, which though unique nevertheless raise the same issues. Water has no intrinisc tendency to become wine: so did the wine that Jesus created at Cana have the true nature of wine, or was it a mere artifact? One may assume that, once in existence, it did all the things that wine by nature does – it metabolised and intoxicated in the drinkers, and the dregs in the glasses degraded to vinegar and entered the food chain. The same is surely true of the loaves and fishes, which certainly didn’t appear by the usual natural processes of growth from seed or from egg. Yet once created, they did nothing but what such things always do by nature. It was as if Tarzan made not a hammock from vines, but a vine indistinguishable from the real thing from raw materials. Jesus did not transubstantiate his raw materials, but transform them: their wineness, breadness and fishyness were not “accidents” but true natures.
So were God to have acted in geological time to create the species we now have – whether by special creation, or by the addition of new information in some way either at the time of speciation or at the beginning, that “intervention” is not what determines the difference between a mere artifact and a true nature, but rather the way in which what he created unfolds.
So I conclude that whilst Thomism leaves room for both Creationist and Evolutionary explanations of life under God’s sovereignty (and all things in between), it does not, actually, decide between them. What it does do is exclude unguided evolution and autonomous nature – which is as salutory to some forms of engineering-biased ID as it is to materialistic Darwinism.