"Prime matter tends to its perfection by acquiring in act a form that it previously had in potency, although it may cease to have the other form that it previously possessed in act. For it is in this way that matter successively receives all the forms to which it is in potency, in order that all of it may be successively reduced to act, which is something that could not be done all at once."

"Whatever is moved, to the extent that it is moved, tends to the divine likeness so that it may be perfected in itself. But a thing is perfect to the extent that it is in act. The intention of everything that exists in potency must be to tend to act through movement. The more an act is poterior and perfect, therefore, the more principally is the appetite of matter directed towards it. Hence, regarding the last and most perfect act that matter can attain, the appetite of matter by which it seeks form must tend as to the ultimate end of generation. But in the acts of the forms there are various gradations. For prime matter is first in potency to the form of an element. When it has the form of an element, it is in potency to the form of a mixed body, because elements are the matter of a mixed body. Considered as having the form of a mixed body, it is in potency to a vegetative soul, for this is the soul that is the act of such a body. Likewise, the vegetative soul is in potency to a sensitive soul, and the sensitive soul to the intellectual soul. The process of generation makes this clear, for first in generation there is the living foetus possessing the kind of life proper to a plant, later that of animal life, and finally the life of a man. No later or more noble form is found in generable and corruptible things after the last form, i.e., the soul of a man. The ultimate end of all generation is, therefore, the human soul and matter tends to this as its ultiamte form. Elements, therefore, are for the sake of mixed bodies, but these latter are for the sake of mixed bodies, but these latter are for the sake of living bodies. In these latter, plants are for the sake of animals; but animals are for the sake of man. Man, therefore, is the end of all generation." (5)

He finds in it, as we have, not only a description of the hierarchy of material forms, but also the tendency among them to be transformed into higher forms until they reach their final goal in the human form. Thus, a material form has not only a natural goal of realizing itself, but a "transnatural" one in relationship to a higher form. And if this transnatural tendency were to be extended to the dimension of time - something that is not found in St. Thomas, himself - then we would have the philosophical foundations for a Thomist view of evolution. Maritain begins to develop these foundations by scrutinizing the phrase in this passage from the Summa Contra Gentiles where St. Thomas compares this ascent of the form to human generation. The foetus first has a vegetative soul, then a sensitive or animal soul, and finally, a human soul, and at each of these transitions there is, according to St. Thomas, a substantial change or transformation involved. A genuine substantial change means the vegetative soul disappears and a sensitive soul takes its place, and then the sensitive soul, in its turn, disappears, and is replaced by the human or spiritual soul. But the advent of these new forms requires the proper disposition of the body, which must be duly proportioned and disposed to receive them. The human soul, for example, demands a certain level of development of the brain and the nervous system. Therefore it cannot be formallypresent, that is, present as the substantial form of the organism from conception. When the human soul finally appears, the vegetative and sensitive soul are no longer formally present, but virtually. The whole thrust of their being is taken up and now rooted in this new formal principle. The embryo is destined from the moment of conception to become a human being, and though it it receives in passing a vegetative soul, and then an animal an soul, in a certain way the human soul is virtually present from the beginning. We have already encountered the but word virtual in the first context where it explains how egg prior forms remain present in higher subsequent forms, but what about virtual presence in the second context?

What does it mean to say the human soul is virtually present in the embryo? The human soul is present in virtue of the act of generation. The phrase "in virtue of" does not connote the physical transmission of an object, but a reality of the instrumental order. The art of Michelangelo, for example, passes as a certain kind of virtue or force or regulating power through his hand and through his chisel to his sculpture. In a similar way, the artistic vision of a conductor passes through his orchestra and becomes visible in the music created. "I will say that the virtue is a certain form transmitted or communicated, but, here is the capital point, this is not an entitative form informing a thing, (chose), a thing (res), to which it would give its constitution in being. It is a transitive form, it is the form of a movement, not of a being, it is the form of a movement by which the latter is regulated in the impermanence itself of its passage in time." (7) It is a reality that is bound up with formal causality, not efficient causality. This virtue or regulative force is "the form of a caused movement, by which the action of the efficient cause, when it is not instantaneous, regulates for as long as the process of causation endures, all the instrumentality which leads to the final effect." (8)

What does this mean? Let's put it in Norris Clarke's language of action. The action of a being is a self-revelation of its formal nature. It transmits, as it were, according to the wavelength of its own being even when it is not a case of entitative action. In the human act of generation the goal is a new human being, but it is a goal that cannot be realized all at once. Something must guide this process or evolution of motion, and inform it to be the kind of motion to produce the specific goal. Or in the language of action, the parents' action of generation has a specifically human character, a force or energy, that directs the growth of the embryo so that it can evolve through the vegetative and sensitive stages and become disposed for the reception of a human soul. This force or energy is not an efficient cause or a thing, but an information or virtue that directs the fertilized egg as its instrument.

The fertilized human egg has a vegetative soul, but human nature is virtually present in it because of the virtue of the human act of generation that passes in and through it. This virtue is the form, as it were, of the evolutionary movement. It is the energy that directs the evolution of the new organism and it directs it until this organism has properties that are such that it can no longer remain directed by its present substantial form, but needs to be informed by another and higher form. Thus, the vegetative soul gives way to a sensitive one, and the sensitive one to the ultimate disposition for a human or spiritual soul. But because this spiritual soul is not a material being - it lacks that substantial potency to substantial existence we call matter - the soul must be immediately created and infused by God. In this infusion the generative force of the parents reaches its final conclusion, and the human soul is no longer virtually present, but formally Maritain develops this theme at length because he is going to apply it to the evolution of the human species. The natural world presents us with a remarkable spectacle in which we find both the fixity of certain species over long periods of time, as well as an evolutionary movement, "which traverses or (rather) has traversed the world of living creatures..." (9) In normal animal generation the offspring are of the same species as their parents. But in animal evolution there is the generation of offspring which have sensitive souls more elevated than those of their parents, and thus are a new species. In the first case, God as the cause of all being exercises a simple directive motion, but in the second, God exercises "an elevating and transforming motion (surr!16vatrice et surformatrice)." (10) The first motion moves the animal to act to produce an animal soul like its own. The second moves the animal to become in its descendents greater than it is in itself.

To sum up: St. Thomas has described the tendency for one material form to become another. If this tendency is put in the context of time we begin to have a philosophical view of evolution. A living being strives not only to perfect itself, and perpetuate itself according to its own species, but at certain times under the influence of this elevating and transforming causality of God, it becomes more than itself in its descendents. This is a special case of the transnatural ontological aspiration that material creatures possess that urges them to become other than what they are. In normal animal embryological development the dynamism of nature suffices under the general directing motion of God - here we can recall the text of St. Thomas cited in Chapter 4 where he insists that the causality of God does not do away with the causality of creatures, but empowers it. In contrast, animal evolution presupposes a special elevating and transforming motion on the part of God which awakens in the creature the ontological possibility of transforming itself.

But when we arrive at the appearance of the first human being even this general philosophical theory of evolution is not adequate. For paleontologists the hominids seem to exhibit qualities like tool-making that exceed the abilities of animals as we know them. Must we conclude that they were human beings? If we say they were not, we seem to deny the scientific evidence. Yet, if we say that they were, we run into philosophical problems because either they do possess spiritual souls and are true humans, or they do not and are not human. For Maritain the hominids, or prehumans, were the final preparation, or we could even say the final disposition of matter, for the appearance of true human beings. These hominids, caught up in the process of evolution, had a plasticity and animal refinement that animals as we know them today do not exhibit, and they finally arrived close enough to the fundamental divide between material and spiritual creatures that human beings could be born of them. But they were superdeveloped animals, not humans, who were the ancestors of the human race in potency. When these immediate ancestors of the human race had reached their highest degree of development, God, by means of an "exceptional and absolutely unique" (11) elevating and transforming motion, infused spiritual souls into their offspring in the course of their prenatal development.

This is a rather crude sketch of what Maritain felt was a sketch, but it is enough to indicate that a Thomist view of evolution is possible. It gives us a picture of a wave or waves of evolutionary energy passing through fixed species which under this elevating and transforming motion coming from God, become more than themselves and their descendents. When the wave has served its purpose, the fixity of the species reasserts itself. The hominids rise like a special tide in order to prepare the way for the human race, and once human beings appear, that tide recedes.

Not only is a Thomist view of evolution possible, but it is rooted in the very notion of matter. It is of the essence of material creatures to be in substantial potency to their substantial existence because of the lack of intensity or density of their being. But this is the very quality that binds them together in a universe. They intereact with each other. They grow and develop out of each other. They give being and take it away from each other, but not randomly like the blind collision of independent units, but according to an overall design. The universe grows in complexity and consciousness, as Teilhard de Chardin saw so well, and it undergoes that evolutionary development in order to finally arrive at the human race. It can undergo that development only because it is material, and one thing can be in potency to another, can be transformed into another. Material beings have a fundamental plasticity in relationship to each other, for they are parts of the same whole, which is the human universe.