The Beginning of Human Life

We continue our discussion of St. Thomas’s exploration of the beginning and end of human life, and focus upon when a human person comes into existence. Our question: When does a human person come into existence? Our answer: At the moment of conception.

7.5. Parameters and Limits of the Discussion

  1. This discussion is, in a certain respect, ethically “buffered.”
  2. The discussion is, in another respect, doctrinally constrained.
  3. Our review of the debate about the beginning of a human person’s existence will not consider alternatives to hylomorphism.
  4. Our discussion will seek to preserve both good philosophy and good science.

(1) An Ethical “Buffer”

Whether delayed hominization or immediate hominization is true, abortion is gravely morally wrong. The CDF (Congregation for the Doctrine of the Faith) noted this in both 1974 and again in 1987:

This declaration expressly leaves aside the question of the moment when the spiritual soul is infused. There is not a unanimous tradition on this point and authors are as yet in disagreement. For some it dates from the first instant; for others it could not at least precede nidation. It is not within the competence of science to decide between these views, because the existence of an immortal soul is not a question in its field. It is a philosophical problem from which our moral affirmation remains independent for two reasons: (1) supposing a belated animation, there is still nothing less than a human life, preparing for and calling for a soul in which the nature received from parents is completed, (2) on the other hand, it suffices that this presence of the soul be probable (and one can never prove the contrary) in order that the taking of life involve accepting the risk of killing a man, not only waiting for, but already in possession of his soul.

 CDF, “Declaration on Procured Abortion” (18 Nov 1974); note 19

Certainly no experimental datum can be in itself sufficient to bring us to the recognition of a spiritual soul; nevertheless, the conclusions of science regarding the human embryo provide a valuable indication for discerning by the use of reason a personal presence at the moment of this first appearance of a human life: how could a human individual not be a human person? The Magisterium has not expressly committed itself to an affirmation of a philosophical nature, but it constantly reaffirms the moral condemnation of any kind of procured abortion. This teaching has not been changed and is unchangeable. Thus the fruit of human generation, from the first moment of its existence, that is to say from the moment the zygote has formed, demands the unconditional respect that is morally due to the human being in his bodily and spiritual totality.

CDF, Donum Vitae, or, “Instruction on Respect for Human Life in its Origin and on the Dignity of Procreation: Replies to Certain Questions of the Day” (22 Feb 1987); I.1

While many statements of the magisterium of the Church indicate that immediate hominization is doctrinally sound, there has been to date no dogmatic or infallible definition on this point. As noted above, St. Thomas also maintains that elective or procured abortion at any stage is a grave moral evil. So, our discussion is ethically “buffered” from sliding into such results, even if delayed hominization is true.

(2) Doctrinal Constraints

Still, there are relevant doctrinal constraints that serve to define the context of the immediate versus delayed hominization debate. As the Catechism of the Catholic Church notes (n. 365): “The unity of soul and body is so profound that one has to consider the soul to be the ‘form’ of the body: i.e., it is because of its spiritual soul that the body made of matter becomes a living, human body; spirit and matter, in man, are not two natures united, but rather their union forms a single nature.” This entry in the Catechism footnotes a certain passage from the Council of Vienne (1311–12), which rejects “as erroneous and contrary to the truth of the Catholic faith any doctrine or opinion that rashly asserts that the substance of the rational and intellectual soul is not truly and of itself the form of the human body.”See Denzinger, Enchiridion Symbolorum, n. 902. Akin to the de fide definitions of other ecumenical councils on philosophical topics, however, this does not supplant the need for properly understanding what such a claim means. Faith cannot replace reason, even as it guides it.

This means that we cannot take our philosophical interpretations of modern science too far too quickly and see in certain magisterial statements reasons for rejecting hylomorphism. This is described by Nicanor Austriaco, O.P., “Immediate Hominization from the Systems Perspective,” The National Catholic Bioethics Quarterly 4, no. 4 (2004): 719–38, at 720: “Though the magisterium has not expressly committed itself to an affirmation of a philosophical nature regarding the [exact moment of the] ensoulment of the human person, [theologian Jean] Porter argues—correctly, in my opinion—that this current perspective favors a theory of immediate hominization that attributes personhood to the earliest stages of human embryonic life. If this is true, however, has the Church, in implicitly rejecting the theory of delayed hominization, not also rejected the hylomorphism on which this theory stands? More specifically, Porter asks, has the Church, in favoring immediate hominization, not also rejected the metaphysical principle that matter has to be disposed to form?”

(3) Focus Upon Hylomorphism

Our arguments here will exclude arguments against materialism and dualism. Rather, the goal is to see the positive case that hylomorphism can make in accounting for the beginning of human life. As others have noted, besides, many contemporary versions of materialism and dualism, when answering this question, adopt some form of a Lockean consciousness-criterion for when a person is a person, thereby also asserting that a human being can be without being a human person. (See Eberl, The Nature of Human Persons, 170, and his discussion of version of contemporary materialism and dualisms in this chapter on the beginning of human life, 142–46. If one holds that the post-mortem soul is a not a person, this would arguably be a different sort of being human without being a person, and for different reasons. )

(4) Good Philosophy and Good Science Cannot Conflict

Lastly, we assume as an operative principle that sound philosophy (in particular, the philosophy of nature and metaphysics) cannot conflict with sound science (in particular, biological investigations and human embryology). “Good science cannot replace good philosophy.” (Austriaco, “Immediate Hominization,” 721) The converse is also true, albeit good philosophy comes to be without science. In this vein, we will seek the fundamentals of good philosophy and science here, without getting into complex cases (e.g., twinning, mutations, developmental aberrations, or biotechnological manipulations).

By contrast, there have been some interpreters who maintain that the Thomistic position is chained to its metaphysics. For instance, “Donceel’s claim is that Aquinas’s conceptualization of a succession of souls [in delayed hominization] is valid regardless of the [biological] facts of generation.” (Stephen J. Heaney, “Aquinas and the Presence of the Human Rational Soul in the Early Embryo,” The Thomist 56, no. 1 (1992): 19–48, at 29) Or, again, others think that St. Thomas’s philosophical position on the beginning of human life is not a biological one but, at the same time, appear to deny that we can coherently attempt to update that philosophical position with better biology. (See Fabrizio Amerini, Aquinas on the Beginning and End of Human Life (Cambridge, MA: Harvard University Press, 2013), 229–30: “As has been emphasized many times, Thomas’s is a philosophical account, not a biological account, of the phenomena of generation, and like all philosophical accounts, his is confined to ordering phenomena according to certain general forms that claim to conform to and replicate the conceptually causal connections found at the macroscopic level among the observed phenomena.” See also 219–21.)

Instead, by seeking a harmony between natural philosophy and biological science, we will, on the one hand, attempt to preserve what is sound about hylomorphism in its fundamental principles. (See Benedict Ashley, O.P., and Albert Moraczewski, O.P., “Cloning, Aquinas, and the Embryonic Person,” The National Catholic Bioethics Quarterly 1, no. 2 (2001): 189–201 (, at 195 for a programmatic statement.) On the other hand, we will see that certain specific applications of Aquinas’s philosophical claims really do require his biological starting points. (See Carl A. Vater, “The Role of the Virtus Formativa in St. Thomas Aquinas’s Account of Embryogenesis,” The Thomist 82, no. 1 (2018): 113–32, at 114.) The old must be pruned wherever false and the new grafted to it wherever true. Let us not imitate those “philosophers, who, throwing aside the patrimony of ancient wisdom, chose rather to build up a new edifice than to strengthen and complete the old by aid of the new [vetera novis augere et perficere].” (Pope Leo XIII, Aeterni Patris, n. 24)

7.6. Central Principles of the Aristotelian-Thomistic Analysis

There are three essential principles to recall, and they imply or implicate others.

(1) The Soul as the Act of the Body

The Aristotelian definition of the soul is the first act of a naturally organized body having life potentially. Recall some essential points about how to understand this definition:

  • The first act of a thing is in contrast to further acts (to be a dog is not to bark), and stands in relationship to a first potency (the potency to be a dog is not the potency to be able to bark). This first act is also unified (substantial form is one), and thus cannot be caused in a segmented or stage-like fashion.
  • Naturally organized” is in contrast to not only artifice or chance, but also the matter which is simple or homogenous.
  • Life is an operation and defined by them (e.g., eating, sleeping, seeing, etc.).
  • The “potentially” in the definition means that the body in question, due to its first act, is able to exercise the operations of life.
    • There are, however, layers of potentiality. We must keep distinct:
    • Active versus passive potentiality (or, power versus potency)
    • Remote or natural active potentiality versus proximate active potentiality (e.g., being able to learn Spanish versus being able to speak Spanish; see Eberl, The Nature of Human Persons, 149–51 for a helpful discussion.)

(2) The Matter-Form Disposition Principle

This principle has already come up in our discussion: recall ScG, II.90, where St. Thomas argues that there is a certain fitting or disposed matter for the human body. He excludes, for example, the possibility that the rational soul could be the first act of a simple body (e.g., a gas). In general, what the matter-form disposition principle means is that matter and form must be proportioned to each other. More specifically, this means that a soul cannot inform just any body: “God could not put a human soul in a rock, or a tulip, or even a kitten, because their bodies are not properly disposed to intellection.” (Vater, “The Role of the Virtus Formativa in St. Thomas Aquinas’s Account of Embryogenesis,” 115–16) (Think about how this principle is true in other areas; e.g., in art or craft.)

Recall from ScG, II.71, that the soul is united to the body without mediation. No additional accident or cause intrinsic to the composite is needed to explain why they are joined. This immediate coherence between form and matter is captured in the matter-form disposition principle: matter that is united to its form must have the proper disposition or relationship for that given level of substantial form, and to lose that disposition is to be destroyed as that kind of thing.

The matter-form disposition principle in specific details flows from Aristotle’s biological-and-philosophical analysis of living things. Considering whether or not the embryo could actually contain the vegetative, sensitive, and rational souls, Aristotle argues: “Now, that it is impossible for them all to preexist is clear from this consideration. Plainly those principles whose activity is bodily cannot exist without a body, e.g. walking cannot exist without feet. For the same reason also they cannot enter from outside.” (Aristotle, De Generatione Animalium, II.3, 736b22–25) Thus, 

It appeared to Aristotle that, at the beginning of its existence, the embryo has no organic structure—in Historia Animalium, he says that early on the embryo “consisted of a fleshlike substance without distinction of parts” [HA, VII.3, 583b9–11]—and so there is nothing to which a preexisting soul could attach itself. Nor could such a soul be introduced from without, since it would have to have in its exterior state a supporting structure; but the sperm, like the embryo itself, is (according to Aristotle) without any such structure. He goes on immediately to add that, since reason’s activity is not bodily—indeed, as he puts it, “no bodily activity has a part in the activity of reason” [GA, II.3, 736b28–29]—it alone enters from outside and so is divine.

Maureen L. Condic and Kevin L. Flannery, “A Contemporary Aristotelian Embryology,” Nova et Vetera (English Edition) 12, no. 2 (2014): 495–508, at 498.

At the same time, however, Aristotle recognizes that, even for the embryo, there must be “feet”:

When Aristotle says that the vegetative, sensitive, and rational souls cannot be present in the embryo until a supporting organ is present, he does not mean that the full organ must be there, “up and running”; he means only that there must be something there—something with organic structure—that will become such an organ and that is moving on its own in that direction.


This understanding of the matter-form disposition principle means that it is not necessary that the “having life potentially” which defines the bodily subject of the soul be the most proximate potentiality possible. Indeed, the philosophical development of this matter-form disposition principle arises from analogies to art, including both matter-form analogies and craftsman analogies, from what is better known to us to what is better known by nature or in itself, and this implies that we can reapply matter-form analogies and correct them when the need arises.

If the matter-form disposition principle can be so understood in a more flexible way than an “up and running” condition or as most proximate to active potentiality, then “The chief question to ask in understanding that theory is ‘What determines whether a human body is proportionate to ensoulment by an intellectual form so as to constitute a human person and not merely a collection of human cells with the passive potentiality to become a human person, as the theory of delayed hominization claims?’” (Ashley and Moraczewski, “Cloning, Aquinas, and the Embryonic Person,” 199)

(3) Parts of the Soul

Recall that, in ScG, II.72, St. Thomas argued that the soul is in the whole body: “That [the soul] is the substantial form both of the whole and of the parts is clear from the fact that both the whole and the parts take their species from it. Hence, when it departs, neither whole nor parts retain the same species: for the eye or flesh of a dead person are only so called equivocally.” Yet, at the same time, the soul has parts:

Nor is it inconsistent that the soul, since it is a simple form, should be the act of parts so various. For the matter of every form is adapted to it according to its requirements. Now the more noble and simple a form is, the greater is its power. Consequently, the soul, which is the noblest of the lower forms, is manifold in power and has many operations, though simple in substance. Therefore, it needs various organs in order to accomplish its operations, of which organs the various powers of the soul are said to be the acts—for instance, sight of the eye, hearing of the ears, and so forth. For this reason, perfect animals have the greatest variety of organs, while plants have the least.

Thus, we can say that there are “parts” of the soul in different organs. How should we make sense of this difference?

We could call a “composed whole” that which includes both (a) sensible wholes such as integral, quantitative wholes (as stones are the parts of a whole wall) as well as (b) the essential whole (a thing’s whole nature or essence, whether in reality, the parts being matter and form, or logically, the parts being genus or species). The soul is an essential whole (albeit just a part of the entire essential whole of the composite substance). The composed essential whole gives rise to the “intelligible whole,” which can be defined and is thus called a definable whole. This is similar to the universal whole, which is also called the predicable whole: triangle is this sort of whole, with its species as parts.

The parts of the soul are potestative parts, and in this respect the soul is a potestative whole or a whole in power. This sort of whole is a mean between the composed and the universal whole. 

  • The reason for this is that the universal whole is present to any of its parts with its whole essence and power, and hence can be predicated of its part. The presence of this whole guarantees predicable identity. For example, an equilateral triangle is a triangle, lacking nothing of the essence of triangle and nothing of what the triangle is prior to specification by the difference “having all sides equal.” 
  • The composed whole is not present to its parts with its whole essence and power. So, the stone in a wall is not, in its essence, a wall, and neither does it have the power or virtue of a wall (it cannot shield from the elements like a wall or be the side of a house). 
  • The potestative whole is present to its parts as to its whole essence but not as to all of its power. The soul is such a whole. Its whole essence belongs to each of its parts or faculties but not its whole power. Thus, the power of the human soul are specifically human, but each power does not share in the whole power of the rational soul (e.g., eyesight, digestive powers, etc.).

This idea that the soul as a form is distinct from its powers is an idea St. Thomas defends in many places. The reason is that, because the soul is by definition in act, were the soul and its powers identical, the powers of life would always be active. However, “we observe that what has a soul is not always actual with respect to its vital operations; whence also it is said in the definition of the soul, that it is the act of a body having life potentially; which potentiality, however, does not exclude the soul.” (St. Thomas, Summa Theologiae, Ia, q. 77, a. 1, c.) Thus, the powers of the soul, its potestative parts, arise from what the soul is as a form (they “flow from the essence of the soul” see ibid., a. 6.). Aristotle says this in a striking way: “If an old man should receive a certain kind of eye, he would see just like a young man.” (Aristotle, De Anima, or About the Soul, I.4, 408b21–22) That is, the soul as a formal principle retains the causal power to inform a new organ and, indeed, new matter. The soul is a form as a whole and a form with parts, but in different ways. (See the discussion of Thomas De Koninck, “Persons and Things,” in Recovering Nature: Essays in Natural Philosophy, Ethics, and Metaphysics in Honor of Ralph McInerny, ed. by J. P. O’Callaghan and T. S. Hibbs, 53–67 (South Bend, IN: University of Notre Dame Pess, 1999), at 60–62.)

Indeed, the soul as a form with certain parts also happens in diverse ways:

As we have said already [aa. 5, 6, 7], all the powers of the soul belong to the soul alone as their principle. But some powers belong to the soul alone as their subject; as the intelligence and the will. These powers must remain in the soul, after the destruction of the body. But other powers are subjected in the composite; as all the powers of the sensitive and nutritive parts. Now accidents cannot remain after the destruction of the subject. Wherefore, the composite being destroyed, such powers do not remain actually; but they remain virtually in the soul, as in their principle or root [sed virtute tantum manent in anima, sicut in principio vel radice].

St. Thomas, Summa Theologiae, Ia, q. 77, a. 8, c.

That is, the soul can lose some of its parts, or powers, but those parts remain virtually present. They could be regained if lost—or, as I will argue, gained in the first place.

7.7. Aquinas’s Embryology

St. Thomas’s account of conception and pregnancy follows in its details Aristotle’s biology. Here is one helpful summary:

Following Aristotle, Thomas says that conception comes about from the combination of the man’s sperm and the woman’s menstrual blood. New life begins at the moment of conception, but this life cannot yet be called human life because body of the embryo is not yet organized enough to perform the tasks of a rational, or even sentient, being. Yet, Thomas maintains that the embryo actively performs the acts of nutrition from the beginning and therefore has a nutritive or vegetative soul. From this point, the virtus formativa forms the embryo’s body so that the body begins to develop sense organs. Once these organs develop, a sentient soul is drawn out of the matter, which soul replaces the vegetative soul. It is necessary that the sentient soul replace the vegetative soul because, for Thomas, the soul is the form of the body, and there can only be one form. If there were two forms, as a Platonic separate-forms theory suggests, they would need a third unitary form above them, and since this unifying form is not to be found in a Platonic system, there would be nothing to make things one.15 Having become an animal, the body of the fetus continues to develop, and when it has been properly organized by the virtus formativa God immediately infuses the rational soul into it. Only God can infuse the rational soul because of the immateriality of the soul. Prior to the infusion of the rational soul, all of the development has been able to happen naturally as in the animals, but since this development has been worked by a material power it cannot reach to the level of immateriality, because no effect can be more immaterial than its cause. Thomas concludes that “the generation of an animal is not simply one generation only, but many generations and corruptions succeed one another.”

Vater, “The Role of the Virtus Formativa in St. Thomas Aquinas’s Account of Embryogenesis,” 117–18.

We could arrange St. Thomas’s overall account in the following schema.

StageTexts & Comments
ParentsThe father is the main agent; he provides the semen with the capacity to initiate the process leading up to generation of the human person (boys, day 40; girls, day 90). The mother provides only the matter, her soul play no active role in the generative process or growth.
“Seeds”The soul is not actually in the semen (they had no conception of sperm or ovum), and it only has the power to initiate the material stages of the process leading to the generation of the human being.
“Consequently, the soul is not actually in the semen before the organization of the body, but only potentially or virtually.” (II.89.2a)
“… the semen contains virtually whatever does not surpass a corporeal power.” (II.89.ad8)
Process of GenerationBecause of their observational evidence, the embryo did not gestate but prior stages led to the eventual generation of the embryo, which then grew to its birth size. One could not hold that a posterior soul generated itself. So, a virtus formativa was needed to explain the process of stage-like generation.
“[The virtus formativa] causes the formation of the body insofar as it operates by power of the father’s soul, to whom generation is ascribed as the principal agent, and not by power of the soul of the person conceived, even after the soul is in that person: for the subject conceived does not generate itself, but is generated by the father.” (II.89.6)
“Accordingly, this formative power remains the same in the aforesaid spirit from the beginning of the formation until the end.” (II.89.7)
The “Embryo” and Stages of Ensoulment“Yet the species of the subject formed does not remain the same, because at first it has the form of semen, afterwards of blood, and so onwards until it arrives at its final complement. … therefore there are a number of generations and corruptions following one another.” (II.89.7)
“Accordingly, the human body precedes the soul in point of time, considered as in potency to the soul and as not yet having a soul, but then it is human not actually, but only potentially. On the other hand, when it is human actually as being perfected by the human soul, it neither precedes nor follows the soul, but is simultaneous with it.” (II.89.ad6)
“Nor is it unreasonable if one of the intermediates be generated and then at once interrupted, because the intermediate stages do not have a complete species but are on the way to a species: hence they are generated not so that they may remain, but that the final term of generation may be reached through them.” (II.89.8)
Infusion of Rational Soul“Therefore, the vegetative soul, which comes first when the embryo lives the life of a plant, is corrupted, and is succeeded by a more perfect soul which is both nutritive and sensitive, and then the embryo lives an animal life. When this is corrupted, it is succeeded by the rational soul introduced from without, although the preceding souls were produced by the power in the semen.” (II.89.9)
“Since, then, every active force of nature is compared to God as an instrument is compared to the first and principal agent, nothing hinders the action of nature from terminating in a part of man and not in the whole (which is the effect of God’s action) in one and the same subject generated which is a man. Accordingly, the human body is fashioned at the same time both by the power of God as the principal and first agent, and by the power of the semen as secondary agent, but God’s action produces the human soul, which the seminal power cannot produce, but to which it disposes.” (II.89.ad3)

From this, note in particular (1) how the species of the embryo is incomplete, (2) that it is not literally a plant or an animal in the stages preceding the rational soul, and (3) that the rational soul contains and subsumes all the life activities of the prior souls.

One key idea to realize is that the process crucially depends upon the virtus formativa, for one soul cannot of itself naturally develop into a higher form of soul. The virtus formativa was essentially the instrumental agent cause that guided the stage-like process of preparations for the final generation of the human being and the infusion of the rational soul. If the prior souls did this, the process would be unnatural or violent.

Without the virtus formativa, Thomas’s system of successive generations and corruptions of souls in the embryo cannot account for the continued development of the body that leads to the successive generations and corruptions. The vegetative soul of the embryo will not cause the embryo to develop sense organs. If the embryo does not already have a rational soul at conception, then some power must be present to guide its development beyond what is necessary for vegetative life.

Vater, ibid., 130–31.

Other authors note this problem as well. (See Heaney, “Aquinas and the Presence of the Human Rational Soul in the Early Embryo,” 27–31; the difficulties are also discussed in many places by Amerini in Aquinas on the Beginning and End of Human Life.) Indeed, “Without the power of the soul of the begetter [and thus the virtus formativa], Aquinas clearly would have nowhere else to turn but to the soul of the begotten to explain this development.” (Heaney, “Aquinas and the Presence of the Human Rational Soul in the Early Embryo,” 31.)

According to Aquinas, the early embryo is not an organism gestating but an organism undergoing a preparatory process for generation. Thus, if we can (1) redeploy the matter-form disposition principle based upon (2) updated biological data which includes (3) the requisite causal power for gestation of a fully-human organism (albeit at an early stage of development), then we could conclude that the human soul is present from conception (what Aquinas would have considered the initial animation).

7.8. Immediate Hominization and Modern Embryology

The thesis will be sketched in what follows. The account will follow various authors in defending the idea that the human rational soul is present from the moment of conception.

(1) Redeploying the Matter-Form Disposition Principle

First, I note that Aquinas himself shows us how flexible the matter-form disposition principle is: “‘[T]he fetal matter is provided by the female. In this matter there is already from the beginning a vegetative soul, not according to second act, but according to first act, like the sensitive soul in one who is sleeping.’ . . . [This text] is saying that it is possible for a soul to be present even though there are no actual organs present.” (Heaney, ibid., 35, 36. Heaney quotes Summa Theologiae, Ia, q. 118, a. 1, ad 4.)

If this is the case, then “In order to account for the required perfections of matter, it does not seem necessary to posit additional substantial forms as preparatives of the matter of the soul. Rather, it would suffice to consider the soul as a causally complex form which itself prepares matter for those operations.” (Ibid., 36. Heaney quotes Rudolph Joseph Gerber, “When Is the Human Soul Infused?” Laval Théologique et Philosophique 22, no. 2 (1966): 234–47 (, at 244.)

(2) Updated Biological Data

It is now a commonplace to say that, from the moment of conception, the human zygote has all sufficient biological resources (DNA, biomolecules, etc.) that are at least intrinsically required for its development. Austriaco develops an argument from systems biology to assist in understanding how the matter-form disposition principle can be redeployed.

From the systems perspective, this particular pattern, this organization of the molecules of the human being, would be a manifestation of his immaterial soul. 

To see how the network of molecular interactions can be said to reflect and manifest the soul, note the parallels between three functions associated with this network and the three functions traditionally associated with the formal principle of an organism. First, the soul makes an organism what it is and determines its end. From a physiological perspective, the net of molecular interactions makes the man what he is and distinguishes him from a lion or a lima bean plant or some other living thing. Furthermore, since life is a deterministic process of molecular transformations, these molecular interactions also define his developmental trajectory and determine his biological end. Second, the soul unifies and integrates an organism, maintaining its identity through changes. As noted above, the human body is in a constant state of molecular flux. Every two years, nearly all of its atoms are replaced. However, the pattern of the molecular interactions remains the same, providing a ground for the substantial unity and identity of an individual with a life span of eighty or more years. Finally, to the ancients, the soul is the source for the powers and capacities of the organism. It is the principle of the being’s nature. Analogously, the net of molecular interactions can also be said to ground the human being’s physiological capacities. To illustrate this, everyone knows that a man is able to see because he has eyes. However, from the systems perspective a man only has eyes because there are molecules in his body that interact to form these eyes. Thus, in the lingo of systems theory, vision is a capacity that emerges from the network of molecular interactions that define the man as a human being. It is also rooted in the soul. With all this in mind, it should be easy to see how the systems perspective can envision a human being as a substance consisting of informed matter, here seen as a single dynamic system of molecules organized in a species-specific configuration.

Austriaco, “Immediate Hominization from the Systems Perspective,” 726–27.

Because the biomolecular network or system is human-specific, and in its development during gestation lacks any systems biology equivalent of substantial changes at stages later than conception itself, Austriaco argues that this is the material disposition requisite for a human soul. As Jason Eberl puts it when discussing a similar line of argument, “The crucial premise here is the claim that possessing the intrinsic potentiality to develop oneself into a fully actualized person suffices for an organism to be a person already.” (Eberl, The Nature of Human Persons, 165.)

(3) Requisite Causal Power

Finally, we need an account of the causal power which guides not generation but gestation. Condic and Flannery argue that this is present in the developmental program of the embryo.

Yet what are the organic parts that constitute the primordia of the nervous system? And is this organic material present from the very beginning? The zygote exists in a very specific state that is uniquely capable of development. There are three basic components of the “program” for development. First, the zygote has specific molecules (transcription factors, enzymes, DNA binding proteins, etc.) that are unique to the embryo and required for a normal pattern of development. Second, the zygote has uniquely modified DNA and associated proteins (i.e., a specific epigenetic state) that is not found in other cell types. Finally, the DNA derived from sperm and egg each carries a particular pattern of maternal and paternal “imprinting” (i.e., chemical alterations to the DNA that regulate how it is used). These three components work together in complex ways to generate all of the cells, tissues, structures, and organs required for life, including the nervous system.

Importantly, this developmental program does not come into existence gradually, but rather all three necessary components are present from the instant of sperm-egg fusion. Further, this program is specifically human (human embryos do not develop into monkeys or oak trees), and uniquely individual (even identical twins do not have identical developmental programs).14 Thus that which is physically required for movement toward the maturation of a particular human body (the primordia of an individual’s mature state) exists from the moment of sperm-egg fusion onward. This program, inherently bound to the very structures of the embryo itself, is the “organ” that contains the principle of movement for the zygote’s subsequent maturation.

 Condic and Flannery, “A Contemporary Aristotelian Embryology,” 500–501. In Maureen L Condic and Samuel B Condic, “Defining Organisms by Organization,” The National Catholic Bioethics Quarterly 5, no. 2 (2005): 331–53 (, at 336n10 they observe: “The systems perspective [of Austriaco] focuses on the molecular composition of the interactive system that constitutes an organism, while the discussion here focuses on organismal function at the cellular level, but the arguments are logically compatible and mutually supportive.”

In other words, “From this fact [all intrinsic causes present for such development], one can infer than an embryo, well before it forms a functioning cerebrum, possesses an active potentiality for rational thought insofar as it has a natural potentiality to develop a capacity in hand to engage in such operations.” (Eberl, The Nature of Human Persons, 153.)

7.9. Further Conclusions

  1. The argument from systems biology is one which we can hold as true with probability (at the very least). We should note carefully how Austriaco emphasizes that “this particular pattern, this organization of the molecules of the human being, would be a manifestation of his immaterial soul.” The pattern is not the soul, yet focusing upon the human-specific biomolecular network is necessary to identify the relevant, disposed matter for the soul. Someone might object that the additions of further “centers” in the network represent substantial changes (and, thus, delayed hominization could be defended), but to my knowledge this is not a necessarily true objection.
  2. The argument made for immediate hominization requires us to say that the intellect is present prior to the existence of the matter that is most proximate to and necessary for its organic instruments, viz., the brain. However, the matter that is present is still specifically human matter and the remote natural potentiality for such organs. It is determined in such a nature as to develop the requisite organs and not others, and no further substantial change is needed for this to happen. (Objection: Is there too much “walking without feet” going on here?)
  3. This argument also requires us to say that—mirroring the post-mortem soul in which the organic powers remain in the essence of the soul in principle or in radice—the various powers of the human soul exist virtually in the zygote, embryo, and fetus throughout gestation as the corresponding organs are developed. (Objection: Is this too much “walking without feet”?)
  4. Generally, we much avoid thinking of the argument as an a prioristic deduction. Rather, working through and extending the analogical structure of potency and act as principles discovered in natural things, we find a natural developmental integrity and fittingness to the existence of a human person from its earliest moments. The “timeline” of the nature and existence of a human person might contain odd stages, but a philosophical analysis of “the truth of human nature” is preferable to an aesthetically or logically “tidy” account. (St. Thomas, Summa Theologiae, Suppl. IIIa, q. 80, a. 4, c.: “A thing is said to belong to the truth of human nature because it belongs properly to the being of human nature, and this is what shares the form of human nature.”)
  5. The assent we can have to the conclusion of the argument is notional assent. It is difficult to comprehend our human nature at its endpoints, at the beginning and end of our earthly lives. We might apply Aristotle’s observation about the heavens to ourselves: “Though we have to pursue our inquiries at a distance—a distance created not so much by our spatial position as by the fact that our senses enable us to perceive very few of the attributes” of such things. (Aristotle, On the Heavens, II.3, 286a4–7) We are so distant from ourselves in our beginnings and endings.

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