Although our main focus in this thesis is on the thought of St. Thomas himself in its historical context, the scientific theory of evolution in our own day appears, at least, to pose so serious a challenge to the Thomistic doctrine of intelligence as the ground of all natural forms that it seems to us appropriate to consider briefly here whether the two positions are compatible and if so what adaptations would have to be made in St. Thomas' teaching to accommodate the data of evolution. The point of conflict arises in the explanation of the origin of new biological forms. According to the most widely accepted evolutionary theory new biological forms emerge throughout the history of the cosmos out of previous ones due, at least in large part, to the interplay of chance factors, the survival of the fittest, etc. Yet, according to the doctrine of St. Thomas which we have just expounded, no natural form can be set up with its intrinsic finality save through the causality of an intelligence, which alone can ground the future-oriented dynamic intentionality of any active nature. There is also no doubt that St. Thomas, following the science of his time–what else could he do?–believed as a matter of fact in the fixity of species, as did the vast majority of scientists right down till the time of Darwin. Hence he had no difficulty in assigning God as the immediate cause of the various species of living beings in the world, following the guidance of the biblical account in the book of Genesis. The opposition between the Thomistic metaphysics of final causality and the theory of evolution seems to be clear-cut.
We have no intention of denying the well-grounded character of the theory of evolution in general. It has fought its way successfully into our contemporary scientific view of the world as the most fruitful hypothesis for explaining the emergence of new biological forms throughout the billions of years of earth's history. Any metaphysical doctrine which found itself in principle opposed to such a well-grounded theory would have to be considered gravely suspect. However, it can be seriously questioned whether such a general theory of evolution requires or has provided–indeed, could provide–any convincing evidence that the process of emergence of new forms takes place totally and exclusively by the working of chance. It would seem to be enough to hold that the interplay of chance factors in the environment plays at least some significant role. Whether or not a provident God, once His existence has been established, actually guides the overall process or intervenes unobtrusively at crucial turning points would be beyond the ability of any scientific techniques or theories either to prove or disprove. What does seem clear, however, is that the constitution of every new living form need not be attributed solely to the direct and immediate intervention of a divine or other supra-cosmic intelligent cause. The fixity of species and the immediate origin of all natural forms from God cannot be made part of a viable metaphysics today.
What adaptations does this require in St. Thomas' doctrine? Although St. Thomas himself undoubtedly did hold as a matter of fact the fixity of species and their direct origin from higher intelligence, there is nothing in his metaphysical principles as such which necessarily requires such a conclusion. Finality, as we have seen, must ultimately be grounded in some intelligent cause as its adequate sufficient reason. But there is no intrinsic reason why this ultimate causality cannot be mediated through other secondary causes, including the interplay of chance factors for the details of evolution, leaving the overall general lines of the whole process intact according to the plan of God. Thus it seems to us that a consistent Thomist could admit as a minimum hypothesis that at least the primary elements of the world-system would have to be set up in their original state by an intelligent cause, which would order their dynamic potentialities and properties toward each other in mutual correlation so that there could be a world at all. Otherwise no interactions could occur at all since there would be no determinate properties; every element would remain in total isolation and nothing further could happen. This basic constitution of the original elements would thereby set up the range of potentialities of these elements to enter into combinations with others, and these combinations in turn to enter into more complex unities, and so forth, thus opening up a vast spectrum of possible future developments, given the appropriate circumstances. The actual detailed working out in space and time of some segment of this range of potentialities could be left in whole or in part to the interplay of chance factors within the context of this basic matrix of intrinsically finalized original elements. This would be a rational way of planning the development of the universe, incorporating into the plan chance factors working according to statistical law, instead of rigidly deterministic laws pre-planning everything in detail. Thus St. Thomas' demand for intelligence at the root of all finality would be preserved intact, but the causality of intelligence would be less direct and immediate, more mediated through non-rational causes, than he himself held. Exactly how much in this whole process, however, would be left to secondary and non-rational causes and how much directly guided and planned by God would be a mystery beyond the penetration of either science or metaphysics.
1 De principiis naturae, c. 31: Efficiens vero dicitur causa respectu finis, cum finis non sit in actu nisi per operationem agentis; sed finis dicitur causa efficientis cum efficiency non operetur nisi per intentionem finis. Et ideo non est causa causalitatis finis, id est, non facit finem esse causam finalem.
2 Paul Alexandre Janet, Final Causes (Edinburgh: T. and T. Clarke, 1883), p. 33: is therefore a sort of cause, but a cause which acts in some fashion before existing; it is an effect which foreseen or predetermined by the efficient cause, has obliged it to take one direction rather than another, it is an end. Paul Janet continues, p. 32: “From all this it follows that the sought for criterion of the final cause is the agreement of the present with the future, the determination of the one by the other.”
3 Summa theologica I, q. 28, a. 2.
5 Schmitz, Disput uber das Teleologische Denken, p. 171.
6 de Régnon, La métaphysique des causes d'après Saint Thomas et Albert Le Grand as quoted by de Raeymaeker, The Philosophy of Being, p. 272: “Hence the intention and the action are united in one and the same term. Thus the end is the bond between the intentional and the efficient order and consequently belongs to both orders. In the efficient order the end is the goal of the operation, finis in re, but antecedently it was in the intentional order …the purpose of the operation, finis in intentione.”
7 Summa theologica, I, q. 44, a. 7; q. 105, a. 5; also, I, q. 2, 5; Summa contra gentiles, III, cc. 2, 3, 16, 18, 22, 24-25, 112.
8 Quaest. disp. de Veritate, q. 22, a. 4.
9 Summa theologica, Ia-IIae, q. 12, a. 5: “prout scilicet ordinat motum alicuius, vel sui vel alterius in finem, quod est rationis tantum.” Cf. also Ia-IIae, q. 12, a. 2; Quaest disp. de Ver., q. 24, a. 2.