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The following are excerpts from “The Zygote and Personhood” written by Dr. Donald DeMarco. These excerpts address the philosophical and scientific questions surrounding the issue of personhood.

Dr. Donald DeMarco is professor emeritus at St. Jerome’s University and an adjunct professor at Holy Apostles College. He is a regular columnist for the St. Austin Review and is the author of 42 books. Some of his latest books, including The 12 Supporting Pillars of the Culture of Life and Why They Are Crumbling are available on Amazon.

Human life begins at fertilization1 when the spermatazoon fuses with the ovum to form a zygote containing 46 chromosomes that bear a genetic code that is different from those of the new human being’s parents. Unlike the gametes from which it was formed, the zygote has the power to, and immediately begins to direct itself through a process of continuous development to become one day what it had begun to be from the outset, namely, a complete human person.

When the zygote has been allowed to have its time, when its potency has become sufficiently translated into act that the organism is recognizable as a human adult, it is clearly a person. But it was a person from the outset in the depths of its being. Throughout the course of its extraordinary development, it was always the same being. There was never the cessation of one being and the commencement of a different being. Continuity marked the essence of its intrinsic development. In this regard, Sir William Liley has stated that “The division of intrauterine life into segments (zygote, fetus, etc.) is a semantic phenomenon, and is in no way supported by biological or medical fact.”2

The human zygote is indeed a prodigious entity. Although it is no larger than a grain of sugar,3 it contains a complete genetic code, all the DNA and all the genes that a complete human being will ever need. The single-cell zygote initiates a development that progresses to the 30-trillion-cell adult.4 At the same time, it exerts biochemical and hormonal influences on the mother as it begins to control and direct the process of pregnancy, a power amplification, considering its minuscule size in relation to that of the mother, that is utterly astonishing. Moreover, it will impress itself, through its DNA, on all the generations of its descendants just as all the generations of its ancestors have impressed their own genotype on it.

The male and female gametes-the male spermatozoon and the female ovum-have a very brief life span. If fertilization does not take place, they soon die. If fertilization does occur, they do not continue their existence as gametes (sperm and ovum) but collaborate to form a new being that possesses within itself a new destiny.

Every being of a biological nature (which is to say, every organism) has an intrinsically ordered relationship between its state at inception and its state at completion. When T. S. Eliot says, “In my end is my beginning,”5 he is echoing the thought of Aristotle and Aquinas, who also understood that what is last in attainment must have been present in some inchoate way at the very outset. Inception and fulfillment are held together by an abiding continuity. Life unfolds, it does not leap (Natura non facit saltus). The zygote is not followed by a series of new natures that represent a juxtaposition of different beings. Rather, it proceeds in its development in an unbroken manner.

In our modern Einsteinian world, the notion of a human zygote unfolding in the context of a space-time continuum, manifesting, with increasingly clear realizations and revelations, the fullness of its being, makes perfect sense.

A zygote neither has consciousness nor resembles an adult human. But consciousness is not a substance but an attribute or function of something that has consciousness. One cannot be consciousness (despite Descartes). One is a being that possesses consciousness. Moreover, appearance is not the same as reality. Richard John Neuhaus exposes the folly of expecting the young embryo to look like the mature adult: “If someone objects that, at five or 15 days, the embryo does not look like a human being, one has only to point out that this is precisely what a human being looks like at five or 15 days of development.”6 Philosopher Stephen Schwarz elaborates:

A person at an earlier stage of his development, say at 4, and later, say 24, is the same person, and is equally a person at both stages. In fact, the whole notion of development here means the development of a person. It is not the development of something into a person . . . but a development within a person who is already there. Thus, the objection that the zygote cannot be a person because it is too undeveloped rests on a false assumption; namely, that to be a person, one must already have reached a certain level of development. On the contrary, if there is development, then the being who reaches it must already be a person. It cannot be that a nonperson reaches this level of development and then becomes a person.7

Development presupposes the existence of that which is undergoing the development. It should be no surprise whatsoever that as a being goes through different stages of development it will look different. If it always looked the same, there could hardly have been any development going on.

In the words of geneticist Jerome Lejeune, “As no other information will enter later into the zygote, the fertilized egg, one is forced to admit that all the necessary and sufficient information to define that particular creature is found together at fertilization.”8

Donald DeMarco, “The Zygote and Personhood,” The Human Life Review, 25th Anniversary Issue Vol. XXVI, No. 2 & 3 (Spring/Summer 2000): 91-98,


  1. The citations from the world of science are innumerable in support of this point. Consider the following: 1) “The fertilized egg is a living entity, a human being, a human individual, and a person, all one and inseparable.” Ward Kischer, “Is the Embryo a Living Human Being? A Human Embryologist Responds,” Social Justice Review, Jan/Feb. 1995, p.16. 2) “It is the penetration of the ovum by the spermatazoon and the resultant mingling of the nuclear material each brings to the union that constitutes the culmination of the process of fertilization and marks the initiation of the life of a new individual.” Bradley Patten, Human Embryology (New York, NY: McGraw Hill, 1968), p. 43a. 3) “A human being does not become a human being but rather is such from the instant of its fertilization.” E. Blechschmidt, “Human Being from the Very First,” eds. Hilgers et aI., Abortion and Social Justice (New York, NY: Sheed & Ward, 1972), p. 7. 4) “Fertilization takes place when the living sperm and living egg cells fuse,” James Bohan, The House of Atreus (Westport, CT: Prager, 1999), p. 25. 5) “This cell [the zygote] results from fertilization of an ovum by a sperm and is the beginning of a human being.” Keith Moore, The Developing Human: Clinically Oriented Embryology (Philadelphia, PA: W. B. Saunders, 1973), p. I.
  2. Robert S. Sassone, The Tiniest Humans, based on interviews with Prof. Jerome Lejeune and Sir William Liley (Stafford, VA: American Life League, 1977), p. 9.
  3. The size of the zygote is 1×10-7 of an inch in diameter. Cf. Edward J. Schwoegler, Ph.D., Human Life: Our Real Beginning, Based on Scientific Evidence (Munster, IN: Schwoegler, 1991), p. 107.
  4. Sassone, 1977, p. 1.
  5. 5. T. S. Eliot, the last line of “East Coker” from his Four Quartets.
  6. Richard John Neuhaus, “Don’t Cross This Threshold,” Wall Street Journal, Oct. 27, 1994, A20.
  7. Stephen Schwarz, The Moral Question of Abortion (Chicago, IL: Loyola University Press, 1990), p. 71.
  8. Jerome Lejeune, The Concentration Can (San Francisco, CA: Ignatius Press, 1990), p. 112.