Today, Public Discourse published an essay by Fr. Nicanor Austriaco, OP, “In Defense of Thomistic Evolution: A Response to Chaberek.” The essay discusses five objections proposed by Fr. Michael Chaberek, OP, in his recent book Aquinas and Evolution. The essay is very short and very interesting, and should be read by all those concerned that Thomistic philosophy is of itself incompatible with the modern science of evolution (as opposed to any ancient theories of evolution—e.g., Empedocles or Lucretius). Portions of this essay have been presented as a talk, “Toward a Thomist Idea of Snake Evolution,” which I have heard a couple times (at the conference of the American Catholic Philosophical Association and at the American Maritain Association conference). I offer the following brief comments.
- Innovation of new kinds of substances?
First, Some might think in general that since St. Thomas held an idea of the fixity of natural biological species (which is notionally distinct from the special creation of species), that this of itself would disqualify his thinking on the subject of philosophy of biology. Fr. Austriaco notes, however, that:
It is striking, however, that he did acknowledge that at least one biological natural kind, the mule, could not have been directly created by God because it is the offspring of two other natural kinds, an ass and a mare, which God had to create first (cf. Summa theologiae I.73.1 ad 3). Nonetheless, Aquinas acknowledged that the creation of the mule could still be attributed to God because mules “existed previously in their causes.”
The text of St. Thomas that Fr. Austriaco cites on this topic is the following, which arises in the context of commenting upon the completion (the perfection and end) of the work of the six days of creation:
Nothing entirely new was afterwards made by God, but all things subsequently made had in a sense been made before in the work of the six days.  Some things, indeed, had a previous existence materially, as the rib from the side of Adam out of which God formed Eve;  whilst others existed not only in matter but also in their causes, as those individual creatures that are now generated existed in the first of their kind.  Species, also, that are new, if any such appear, existed beforehand in various active powers; so that animals, and perhaps even new species of animals, are produced by putrefaction by the power which the stars and elements received at the beginning.  Again, animals of new kinds arise occasionally from the connection of individuals belonging to different species, as the mule is the offspring of an ass and a mare; but even these existed previously in their causes, in the works of the six days.  Some also existed beforehand by way of similitude, as the souls now created.
That is, St. Thomas identifies how various innovations or new beings that come to be are somehow already present in the universe, namely, present in their causes. He identifies five ways (labelled above). Fr. Austriaco discusses the third and fourth of these ways. It is the great burden of a Thomistic theory of evolution to develop the notions of universal causality (the third way), of the causality inherent in natures (the fourth way), and even material causality (the first way) such that Thomistic philosophical principles can be developed in interconnection with evolutionary biological inquiry. Fr. Austriaco’s essay proposes some of these ideas in seed-form. He mentions and uses Maritain’s essay on evolution (“Toward a Thomist Idea of Evolution”) but does not refer to De Koninck’s proposals in The Cosmos (more on this below).
In short, the perfection of the universe can be defended by Thomists today, even if the manifestation of the whole panoply of the universe’s perfections essentially requires a history. Fr. Austriaco’s comments on this topic at the end of his article (attending to the Thomistic doctrine of the end-goal and perfection of the universe) are very helpful and necessary. Indeed, the notion of the universe as a whole (including its kinds as well as its spatial and temporal extent) must be kept firmly in mind when thinking philosophically about what the modern sciences say about its various parts. For instance, in this regard, it is true to claim that, qualifiedly speaking, one species is not more perfect than another when viewed via the lens of biology and taking into account the adaptations of a given kind to its environmental niche (sharks flourish underwater, we do not), simply speaking, in the order of the universe as a whole, the ontological hierarchy of beings is still an open possibility.
- Innovation of the human species?
One should also be aware that St. Thomas, in the context of arguing against the philosophical demonstrability of the eternity of the world, allowed for the innovation of the human species itself, at some specific point in time during the universe. That is, his arguments point out to us that it is philosophically demonstrable that the human species had a beginning in time, even if it is not philosophically demonstrable how this came about.
Objection 8: Further, if the world and generation always were, there have been an infinite number of men. But man’s soul is immortal: therefore an infinite number of human souls would actually now exist, which is impossible. Therefore it can be known with certainty that the world began, and not only is it known by faith.
Reply to Objection 8: Those who hold the eternity of the world evade this reason in many ways. For some do not think it impossible for there to be an actual infinity of souls, as appears from the Metaphysics of Algazel, who says that such a thing is an accidental infinity. But this was disproved above (Q. 7, a. 4). Some say that the soul is corrupted with the body. And some say that of all souls only one will remain. But others, as Augustine says, asserted on this account a circuit of souls—viz. that souls separated from their bodies return again thither after a course of time; a fuller consideration of which matters will be given later. But be it noted that this argument considers only a particular case. Hence one might say that the world was eternal, or least some creature, as an angel, but not man. But we are considering the question in general, as to whether any creature can exist from eternity. (St. Thomas, Summa Theologiae, Ia, q. 46, a. 2)
In this reply, St. Thomas clarifies that the objection’s hypothetical major premise is in error, because it conflates the status of a part of the universe (the human species) with the whole universe. However, for the sake of completeness, we should note that St. Thomas might have changed his mind on this issue, for he writes in On the Eternity of the World (most likely written after the above quotation from the Summa):
Those who try to prove that the world could not have always existed even adduce arguments that the philosophers have considered and solved. Chief among these is the argument from the infinity of souls: if the world had always existed, these people argue, there would necessarily be an infinite number of souls. But this argument is not to the point, for God could have made the world without making men or creatures with souls, or he could have made men when in fact he did make them, even if he had made the rest of the world from eternity. In either case, an infinite number of souls would not remain after the bodies had passed away. Furthermore, it has not yet been demonstrated that God cannot cause an infinite number of things to exist simultaneously. (St. Thomas, On the Eternity of the World, final paragraph)
That is, the final sentence is the one that is disturbing in view of what St. Thomas wrote in the Summa.
Nonetheless, the commentary tradition picks up on this argument from the Summa Theologiae and parallel passages in the Summa contra Gentiles (see Book II, ch. 81) and provides grounds for a philosophical argument that the human species cannot be eternal. Having observed that St. Thomas has distinguished between arguing that the whole universe had a beginning in time from arguing that a part of the universe began in time, Cajetan writes:
For given that man’s having a temporal beginning [hominem incoepisse] is demonstrable, this doubt would yet remain as to whether the beginning of the universe is demonstrable: because the eternity of the world or angels is compatible with the temporal beginning [incoeptione] of man, as is said in the text. (Cajetan, In Ia Summam Theologiam, ad loc.)
And Sylvester of Ferrara writes:
Give then supposition that the world is eternal (and likewise the generation of human beings)—since these three propositions are mutually inconsistent: 1) the world and generation of human beings is eternal, 2) the human soul is immortal, 3) an actually existing infinite is impossible even among things existing apart from matter—it must be said that God had contrived some way in which to avoid the dilemma and not admit of an actually existing infinite, namely: by making [a finite number of] souls circulate from one body to another; or by making souls cease to exist by withdrawing his causal influence (granted that according to their natures they are immortal and incorruptible and intellectual); or by imposing upon things some other order unknown to us. For, just as we say that the world was able to be created from eternity, not on account of some real potency in the world itself to its current existence, but because the power of God alone is able to do so, so also it is not unfitting to say that some other order in created things than exists now could exist through divine power, although we are unable to know that order distinctly. Nor it is necessary to be troubled about what in the world such an order would be. (Sylvester of Ferrara, In Summam contra Gentiles, II.81, n. 6)
Of course, in the era after Darwin, we do indeed worry about what in the world such an order would be!
- The cosmos and secondary causality
Elsewhere in his essay, Fr. Austriaco notes that, in order to preserve the principle of causality, either divine or angelic causality would have to be invoked for how a new species is truly innovated. While he does not cite Charles De Koninck’s essay on evolution (The Cosmos), it bears noting that De Koninck likewise favored a more robust defense of intra- and supra-cosmic agent causality in an evolving cosmos.
Furthermore, De Koninck somewhat modifies the notion of species such that the minute changes discussed in Fr. Austriaco’s article (the steps from a lizard to a snake, for instance) are intra-species changes. That is, De Koninck proposed that only four real species exist (what he calls “philosophical species): the inorganic, the living kind with plant life, with animal life, and the human. Of course, this itself is controversial, and it seems more adequate to the truth of things to fine-grain the divisions a bit more.
Yet based upon this fourfold division, De Koninck requires primary divine causality to sustain the agent causality behind the innovation of any given instance of substantial form (as St. Thomas does; see objection 3 in Fr. Austriaco’s essay) or the innovation of a new substantial form, or evolution. That is, De Koninck recognizes the divine concurrence with secondary agents. Secondary causality can be utilized to explain generation of what would essentially be “philosophical varieties,” while the “leap” from one philosophical species to the other requires divine causality (see objection 1). Nonetheless, the secondary causality of causes within the entire created universe (angels) act upon the physical universe (the cosmos) in order to dispose secondary matter to innovation of these philosophical varieties. (Fr. Austriaco’s use of the notion of the disposition of matter is good, with the exception that he does not explicitly distinguish between secondary and prime matter. Without this distinction the discussion could become muddled.) Thus, on De Koninck’s view, the second objection that Fr. Austriaco answers would be answered in a different way, namely, by denying that the innovation of a snake-kind from a lizard-kind is a substantial innovation in kind.
Nonetheless, this account is less than satisfactory today, given what is known about DNA. De Koninck’s essay The Cosmos, unpublished during his lifetime, was written about two decades before the discovery of DNA, although the “hereditary molecule” had already been discussed by H. J. Muller in 1922. In this respect, and especially with regard to Fr. Austriaco’s reference to his work on the connection between hylomorphism and systems biology (see also the work of Christopher Austin; here, here, and here), the essay deserves a wide readership. Readers should also consider Fr. Austriaco’s recent article in the ACPQ, “Defending Adam After Darwin: On the Origin of Sapiens as a Natural Kind,” and his website (co-authored with other Dominican confreres), Thomistic Evolution.