In the landmark Supreme Court decision of Roe versus Wade, the majority opinion stated that we “need not answer the difficult question of when life begins.” It seems however that this in fact is the fundamental question upon which the abortion debate hinges. As proof that the inmates are running the asylum, the same decision concedes that “(If the) suggestion of personhood [of the preborn] is established, the [abortion rights] case, of course, collapses, for the fetus’ right to life is then guaranteed specifically by the [14th] Amendment.” For those who are in favor of abortion, they often will answer the question of when life begins by making a distinction between a human being and a person. This distinction usually rests upon the presence of the soul in the person. Rarely however is this premise attacked. By using simple philosophy and modern embryology we can find where this assumption is flawed.
To begin it is important to mention that the question of the morality of abortion does not rest upon the question of when the human body is infused with a soul. The Church has always taught that abortion is morally wrong. She has affirmed that “the reality of the human being for the entire span of life, both before and after birth, does not allow us to posit either a change in nature or a gradation in moral value, since it possesses full anthropological and ethical status. The human embryo has, therefore, from the very beginning, the dignity proper to a person” (Dignitatis Personae, 5)
Secondly, from a philosophical point of view there is no such thing as a living being that does not have a soul. The soul is the animating principle of all living things. The Church has baptized Aristotle’s notion of the three types of souls that exist in a nested hierarchy: vegetative, sensitive, and intellectual. Each of these has specific functions. The vegetative soul is concerned with growth, nutrition and reproduction, the sensitive soul is concerned with locomotion and perception and the intellectual soul is concerned with rational thought. These are nested in the sense that anything that has a higher degree of soul also has all of the lower degrees. All living things grow, nourish themselves, and reproduce. Animals not only do that, but also move and perceive. Finally, man does all of the above in addition to reasoning (Aristotle, De Anima¸413, a.23).
With this foundation in place, we can begin to look at the different theories of ensoulment that have been adopted throughout the course of history. These theories fall into two broad categories. The first is usually referred to as “delayed hominization” (or “serial ensoulment theory”) while the second is called “immediate ensoulment theory.” As the name suggests, “immediate ensoulment” refers to the infusion of the soul at conception.
The argument for “Serial ensoulment” is summarized as follows: First, because the soul is the form of the body (i.e. makes the body human), the rational soul cannot be present until there is a body present that is significantly complex and organized to receive the soul. A mere “clump of cells” would not constitute a human body and thus could not receive a human soul. Third, the claim is that there is no human body in the zygote. Therefore the conclusion is that until the soul is present there is no human being. It was Aristotle who first proposed this theory and called it “delayed hominization.”
He speculated that the human soul was received only after the body was properly prepared for it. He thought that the embryo was formed from homogenous menstrual blood of the mother by the action of the semen that remained in the womb for at least forty days. Since this matter was not sufficient enough for the infusion of a human soul, it formed a “pre-person” that had only vegetative functions with a vegetative soul. Once it developed a heart and brain it then became an animal with an animal soul and eventually progressed into a true human being with an intellectual soul. This is similar to what many people argue today when they call the child a “potential person.”
One could also find support based on this idea of delayed hominization for the position of someone like Peter Singer who says that a child may be killed up to 18 months old because they are not yet a person. If we must wait until some (it would have to be arbitrary) milestone of growth is reached before the infusion of a soul then that could happen at any point during development, even outside the womb.
St. Thomas Aquinas agreed with Aristotle and many Catholic thinkers followed his thought. Because Aquinas also had inadequate biological knowledge he thought that the body that was first formed was vegetative in nature and later underwent a substantial change with a new body in which it was animated by an animal soul. A substantial change is one in which a whole new entity comes into existence. It is not mere growth, but the bringing about of a new substance. Finally there was another substantial change that occurred and the now human body was infused with an intellectual soul. It is important to note however that for St. Thomas the infusion of the soul happens at the origin of the human body.
If we apply the principles of modern embryology we can then show where the theory of serial ensoulment is lacking. To say that the body is not “significantly complex and organized to receive the soul” is to grossly misrepresent the nature of the being that results from syngamy. From the moment of fertilization, the new entity carries out precise, self-directed processes. From then on, the only thing necessary for growth and development is the same thing we need—water, food, oxygen and a healthy interaction with its natural environment.
Secondly, to say that “a formal cause is present only in a finished product,” is rather vague. There is no such thing as a “finished product” in the truest sense. Everything is journeying toward perfection. However what does remain to be done in the embryo in order to reach perfection is the successive carrying out of inherent potentialities that are already present in the newly conceived person. Because it has its own unique DNA that is different from either parent and possesses a full genetic program, from this point forward no new genetic info needed to make it into an individual human being. It already is a human being, just at a particular stage of development. Also, because the human body has all of the necessary genetic information and internally directed activity to lead to full development then the human soul must be present.
Although the Church has not definitively rejected the theory of delayed hominization, she teaches with relative confidence that theories of delayed hominization are in fact scientifically obsolete. As the Instruction on Respect for Human Life in Its Origin says, “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?”
There are some today that have speculated ensoulment does not occur until implantation because of the possibility of twinning that occurs between the time of fertilization and implantation. However this viewpoint is implausible because the early embryos develop continuously as individuals during that time. There is not an active potentiality to develop into twins and all of the scientific data points to the possibility of twinning as a passive potentiality. What this means is that there is nothing in the DNA of the child itself to suggest that it will twin. Instead it is acted upon from the outside and performs as a mode of asexual reproduction, akin to cloning.
In conclusion, with the increase in biological knowledge (and St. Thomas would have likely agreed) most Catholic thinkers abandoned the delayed ensoulment theory because they recognized that the body that is formed at conception is a human body. This seems the most reasonable because if the newly conceived child really has a human nature and does not undergo a substantial change then he must have an intellectual soul. Arming ourselves with both philosophy and modern scientific knowledge we can attack this hidden premise and protect human life at its most hidden and vulnerable stage.