“Ensoulment” is the word which describes the point at which the body of the conceptus is said to be informed by a human soul. (The notion of a living being having “no soul” is a philosophical oxymoron, since the soul is the principle of life in a material being.) There are two basic theories of ensoulment. The first is called the “immediate animation, immediate ensoulment theory”; the second, the “immediate animation, delayed ensoulment theory” (also called the “serial ensoulment theory”). As the names suggest, the former asserts that, at the very moment of animation (when life begins), the newly conceived human is animated by a rational soul; while the latter holds that the human soul’s informing of the new body is delayed. This latter theory further holds that there is a progression from vegetative to animal to human soul as the principle of animation. Common in the middle ages, the theory was based on Aristotelian biology and is untenable considering all that is presently known from the empirical sciences. Many learned Catholic authors of the ages of Faith held this theory and advanced it in their writings because it was the accepted biology of the day.
The issue comes into the abortion debate largely by way of abortion advocates advancing the notion that, since men like St. Thomas Aquinas did not believe a human soul actually animated the newly-conceived body for a number of weeks, Catholics are hypocritical for opposing abortion on the grounds that it kills an innocent human being. Of course, this is in itself a species of hypocrisy, given that advances in the sciences of fetology and embryology (as well as genetics) have undone the earlier theory. The abortion advocate using this argument generally presents himself as an “open-minded” individual of a broad scientific culture (one who is “reasonable” as opposed to “dogmatic”), but, by advocating the delayed ensoulment theory, he falls into a senseless retrogression to primitive biology.
Among those who have recently revisited the delayed ensoulment theory are the liberal Jesuit moralist Joseph Donceel and the feminist ideologue, Rosemary Reuther.
The issue thus briefly being outlined, it would be appropriate to give a summary and refutation of the delayed ensoulment (or serial ensoulment) theory, followed by what Dr. Hogan calls “a more economical theory of ensoulment”, i.e., one consonant with science, reason, and the truths of the Faith.
From the class notes, the serial ensoulment theory is thus summarized: “First because the soul is the substantial form of the body, the rational soul cannot be present until there is a body present that is significantly complex and organized to receive the soul. Second, a formal cause is present only in a finished product. An actual human soul cannot be united with a virtual human body. Third, there is no human body in the zygote. Fourth inasmuch as all the positive features of the human body derive from the soul, until the soul is present there is no human being.”
The first point underestimates the nature of the new entity which results from syngamy. The numerous processes carried out with ordered precision (such as chromosomes borne by the pronucleus of each gamete conjugating along the mitotic spindle) present us with the new entity’s impressive complexity, something unknown before modern scientific discoveries. The second point again underestimates the zygote, the genotype of which is already established. What remains to be done after syngamy is merely the successive actualization of the active potentialities already there in this present reality, this being in act. Third, although the zygote is not a fully developed human body, that body is really present in the active natural potentiality of the zygote. The fourth point states a truism we gladly embrace. Having all the necessary genetic information and immanent activity heading towards full maturation, the full development of the human body is already in dynamic process; therefore, the human soul must be there.
We end with the “more economical theory of ensoulment”: The rational soul is present from the instant of conception as the principle which orders the complex immanent functions following syngamy. It is operating at first only with its lower faculties, anticipating the higher biological functions as it will later, in the neonate, anticipate both the use of reason and adult biological development. In the earlier stages its presence is comparable to the presence of the rational soul in one comatose. When the natural active potencies innate in the conceptus have been successively actuated, the full complement of human faculties will be manifest and the soul will be operating at the vegetative, sentient, and rational level.