"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 [implantation]. 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 else 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."
Sacred Congregation for the Doctrine of the Faith, Declaration on Procured Abortion (November 18, 1974), note 19. See 4 Origins 385-392 (December 12, 1974) at 392.
"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."
Congregation for the Doctrine of the Faith, Instruction on Respect for Human Life in its Origin and on the Dignity of Procreation, March 10, 1987. See 16 Origins 697-711 (March 19, 1987) at 701.
"We share the conviction expressed last year by the select committee commissioned by the Australian Parliament to study this issue that 'no one event succeeding fertilization is such that it can bear the weight that some would attach to it' for the purpose of justifying harmful experiments prior to that event. The newly conceived member of the human species should be accorded the respect due to a human subject at every stage."
Richard Doerflinger, Testimony on behalf of the NCCB Committee for Pro-Life Activities before the House Select Committee on Children, Youth and Families, May 21, 1987 [citing Senate Select Committee on the Human Embryo Experimentation Bill 1985, Human Embryo Experimentation in Australia (Australian Government Publishing Service, Canberra 1986), p. 26, No. 3.9]. See 17 Origins 143-4 (July 30, 1987) at 143.
"The formation of the embryonic disk, and within that disk the epiblast, at about day seven, is a differentiation at least equally significant [as that occurring at about day 14]; in the epiblast are all or virtually all the 'embryo proper' cells. Indeed, the inner cell mass has differentiated from other parts of the embryo by about day five, and functional differentiation of the cells in the embryo begins even earlier...The fact that some days elapse before one can identify which cells will become placenta and which 'embryo proper' in no way justifies any claim that during those days there is something other than an individual, self-developing human organism, fully continuous with -- the very same individual being as -- the adult human organism."
Joint Committee on Bioethical Issues of the Catholic Bishops of Great Britain, Statement responding to recommendations of the British government's Warnock Committee, July 9, 1987. See 17 Origins 144-7 (July 30, 1987) at 145.
"Despite the facts about twinning, chimeras, and so on, most unborn babies with their accessory tissues develop from a single zygote and are alone in developing from that zygote. Unless the facts support [the] theory that the baby is formed at the primitive streak stage from a few thousand distinct individuals (the "mass" of cells), in most cases individuality will have to be admitted to appear to be continuous, and there will be no reason to deny it, unless the arguments from twinning, chimeras, and so on by themselves plainly show that a substantial change is absolutely required -- for example, at the primitive streak stage...Now, the evidence does not support [the] theory that cell division gives rise to really distinct individuals until a small army of them form the true human individual...[T]he cells and tissues...are always working together harmoniously, which is to be expected if they are, not a mass of distinct individuals, but integral parts of one developing individual."
Germain Grisez, "When Do People Begin?", in Schrenk (ed.), The Ethics of Having Children, 63 Proceedings of the American Catholic Philosophical Association 27-47 (1989) at 37-38.
[Regarding the claim that even the "biologically perfect" preimplantation embryo cannot yet be a human individual because it can sometimes develop into a hydatidiform mole]: "The suggestion that CHM [complete hydatidiform moles] originate from "biologically perfect" embryos, i.e., from embryos which could as well develop into a human adult...is falsified by observations. Eggs which develop into CHM carry a gross chromosomal aberration and are from the point of view of the developing capacity equivalent to sperms, oocytes, or isolated epithelial cells, i.e., on principle they cannot develop to term; the same is true of the majority of eggs which are spontaneously aborted: it is well known today that such eggs cannot develop to term because of gross chromosomal or structural anomalies...Such eggs should not be called embryos...The preimplantation embryo is the same individual of the human species (the same human animal) as the adult into whom the preimplantation embryo can in principle develop."
Antoine Suarez, Dr.sc.nat. ETH (Interdisciplinary Study Center The Human Embryo, Zürich, Switzerland), "Hydatidiform Moles and Teratomas Confirm the Human Identity of the Preimplantation Embryo," 15 The Journal of Medicine and Philosophy 627-35 (December 1990) at 629-31.
"The very young human being, just after fertilization...has split in two cells and then in three cells...curiously we do not split ourselves in two, four, eight and continue like that...We split in two cells of roughly equal dimension and one of the two cells splits in two...after that stage of three cells, it starts again, it comes to four, and it continues by multiples of two...[W]hen we split at the beginning of our life (two cells and then one cell in two), we go at a three cell stage. It's probably at that time that a message goes from one cell to the two other cells, come back to the first one and suddenly realize we are not a population of cells. We are bound to be an individual. That is individualization, that makes a difference between a population of cells which is just tissue culture and an individual which will build himself according to his own rule, is demonstrated at the three cell stage, that is very soon after fertilization has occurred."
Jerome Lejeune, M.D., Ph.D., Testimony in Davis v. Davis (Circuit Court for Blount County, Tennessee at Maryville, Equity Division (Div. I), No. E-14496), August 10, 1989.