I’ve finished a booklet on evolution and creation, which should be published soon. In the next few posts I’ll be putting up some selections from it.
St. Thomas Aquinas gives precise formulation to the scriptural and patristic teaching: to call God the Creator means that all “being” comes from him, that is, the existence of anything whatsoever comes from God, and depends essentially upon him. “Being” here includes being active, and so the activity and power of everything derives from God’s creative action.
St. Thomas sees the power of God’s creative action not only in making things exist, but above all in making them be causes of other things. The production of one creature by another does not compete with God’s causality, as though a creature had to be either from God or from another creature. Rather, whatever is produced by a creature comes from God as the first and ultimate cause of it, and from the creature as a secondary cause. (We are speaking, of course, about real beings that are produced; sin, as a moral defect and privation, is not from God.) Since God is the cause of all other causes, his causality includes even chance events, which occur by the coincidence of two causes.
St. Thomas sees the ability of one natural being to be generated by another natural being as rooted in “first matter,” the radical possibility of a material being to become one thing or another. When a natural agent forms a structure suited for the living activities of growth, etc., the result is not merely a complex structure, like a machine, but really becomes a living being. Yet while matter is necessary for this change, the change itself cannot be attributed only to the matter, which is merely the inner root of the possibility of being a living being; the change must ultimately be attributed to the cause of matter, which is God. This is true not only of the human soul, which in a certain manner transcends material reality, but of every nature, which is something more than the stuff in which it is found. The existence of a natural being cannot be attributed only to that which materially formed it, but must also be attributed to the author of nature.
Since created things receive from God not only existence, but also the power to be causes of other things, Thomas’s view of creation leaves room for a natural sequence such as evolution in the created world, whereby one type of living being comes from another. We cannot determine a priori the extent to which this can or does happen concretely. We cannot say a priori, for example, that a living being can only produce something essentially like itself, but can only make a judgment about this on the basis of experience. St. Thomas, in fact, following Aristotle and the common scientific opinion, held that simpler living beings are generated by the powers of the heavens (we might say, by “natural forces”) acting upon inanimate substances, while more complex living beings are generated by other living beings like them in kind. He believed this not for purely theoretical reasons, but because he saw it as the best account given the data available. This particular account of abiogenesis (“spontaneous generation”) has been falsified, at least as regards the living beings we see commonly around us. But the general possibility of life being generated through natural forces remains open, as does the possibility of one kind of organism generating another kind. It is the task of empirical science to determine whether, when, and how this actually happens.