Human embryos, too tiny to see with the naked eye, have been at the center of significant debate in both the scientific and political arena since the legalization of abortion. That debate has only intensified since the introduction of in vitro fertilization and more recently the demand from many corners for wide-open embryonic stem cell research.

Since the defense of the human embryo is our major concern in these ongoing controversies, I think that it would be extremely valuable for us to examine and clarify for ourselves the Church's teaching about the moral status of the human embryo. What does the Church say about the human embryo and why?

Let's get right to the heart of the issue. Is the human embryo a human being? It may not surprise you to hear that the answer is an unequivocal yes! Of course the human embryo is a human being. What may surprise you is that in proclaiming this truth the Church does not refer to scriptural revelation but to clear scientific evidence.

Let's divide the question: Is it human? What else might it be? It has a uniquely human genetic signature. No scientist could examine the chromosomes of the human embryo and come to any conclusion other than it is human. It's certainly not an aardvark or a polar bear.

Second question: Is it a being? Some have argued that it is "part of the mother's body" and simply akin to any other body cell that has the full complement of human DNA in its nucleus. They argue that nobody would call a skin or hair cell a human being, even though it is a human cell.

However, again, we can simply refer to science. In any solid biological curriculum, embryology is studied as a separate discipline from cell biology. Why? Because science has recognized for decades that the embryo is a different entity than a cell. A human skin cell, in and of itself remains a skin cell, it cannot become a human being. An embryo rather has both the genetic directions and the self-organization to mature. It therefore is a being, not simply a part of a being. Left to itself in its proper environment it will develop into an adult human being, not something other than a human being and not a part of a human being.

This teaching was beautifully summed up in the church's Declaration on Procured Abortion (1974):

"…from the time that the ovum is fertilized, a life is begun which is neither that of the father nor the mother; it is rather the life of a new human being with his/her own growth. It would never be made human if it were not human already. This has always been clear and…modern genetic science offers clear confirmation…from the first instant there is established the program of what this living being will be: a person… Right from fertilization the adventure of a human life begins…"(nos. 12-13).

You may have heard some critics of the Church's defense of the human embryo speak of a something known as "delayed hominisation." The term refers to the theory that God does not infuse a soul into the human embryo until some time after it has been conceived. Such critics claim that such a theory might allow for the abortion of an embryo prior to its reception of a soul.

In fact, our critics are correct only to the extent that such a theory does exist in the teachings of some Catholic theologians, including, surprisingly to many, of St. Thomas Aquinas himself. Such theologians taught that the early embryo needed a time of material development in order to be disposed to receive a soul. Hence they believed there could be a delay between the conception of the human embryo and the presence of a human person (a human being with a soul).

What does the Church say about such a theory? Was St. Thomas a heretic? In fact, in the same document quoted above, the Church replies to this issue, again in what may seem to be a surprising manner: The present Declaration deliberately leaves untouched the question of the moment when the spiritual soul is infused. The tradition is not unanimous in its answer and authors hold different views… (footnote n. 19).

Nevertheless, while the Church in her own words, "leaves untouched the question of the moment when the spiritual soul is infused" our critics are wrong in believing that such a theory might open the door to abortion. In fact, the church remains unambiguous about the moral status of the human embryo. The human embryo is a human being and as such demands unconditional protection. While there have been various theological discussions in the Church over the centuries about the moment of ensoulment, there has been a constant, unconditional and unwavering condemnation of abortion.

The first non-biblical Christian text, the Didaché, which dates from the end of the first century, makes it clear that for the Christian abortion is forbidden. Even if the soul is infused after conception, the church defends the human embryo because 1) it is a human being (as even science makes clear), and 2) if the infusion of the soul at conception is even probable (which it certainly is), then abortion kills a human being already in possession of a soul.

In our defense of the human embryo, we Catholics need not deny a tradition that includes those who have made a distinction between a human being (pre-soul) and a human person (ensouled) because this philosophical debate does not now, nor has it ever affected the Catholic understanding of moral status of the embryo. Perhaps this is best summed up in the words of Pope John Paul II:

"…Over and above all scientific debates and those philosophical affirmations to which the Magisterium has not expressly committed itself, the Church has always taught and continues to teach that the result of human procreation, from the first moment of its existence, must be guaranteed that unconditional respect which is morally due to the human being in his or her totality… The human being is to be respected and treated as a human person from the moment of conception" (Evangelium Vitae, 60).

Vincentian Father Richard Benson is academic dean and professor of moral theology at St. John's Seminary, Camarillo. His column appears monthly in The Tidings