Some questions never go away, even those we think we’ve answered once and for all. One of those questions concerns the beginning of human life: when we as human beings actually come into existence. This is a biological issue, intimately linked to, yet independent of, the philosophical or theological matter of when the child in utero can be judged to be a “person.”

Any number of answers have been given to the question of when life begins. Alternatives are at fertilization, with formation of the one-celled zygote; at implantation, when the developing embryo attaches to the uterine wall and undergoes a radical change known as gastrulation or organogenesis; at quickening, when the mother first feels the child move in her womb; at birth, as the newborn infant gulps his or her first lungful of air; or at some later date, once the child has proven itself free of genetic and other disabilities and can lead a “productive” life.

Only the first two of these deserve to be taken seriously.

Christians of all traditions are divided over whether animation is immediate or delayed: whether the embryo is ensouled from fertilization, or whether it becomes ensouled (and hence truly human) only with implantation. Orthodox Christians tend to favor the former view; many Roman Catholics and Protestants hold the latter.

At the end of a talk I gave recently on the manipulation of embryos, a woman approached me and identified herself as a Catholic bioethicist who had long worked in the field of embryology. In her view, the embryo prior to implantation is properly referred to as a “pre-embryo,” since it is characterized by two conditions that are lost with implantation. First, the individual cells or blastomeres are “totipotent”; that is, each one contains the full complement of DNA—the entire, unique genome—and is potentially able to grow independently into a living being. Second, there is a huge percentage of “wastage” among pre-implantation embryos. Between 55% and 75% of all embryos are expelled spontaneously from the mother’s body, without her ever knowing she was pregnant. These “mini-miscarriages,” coupled with the phenomenon of “totipotency,” lead many, if not most people today to regard the pre-implantation embryo as (in this bioethicist’s terms) a “substratum” of human existence, but not as actual human life. It is the essential precondition for the development of human life, but it is wrong to confuse it with an individual human being as such, particularly since twinning can occur during the pre-implantation period.

This understanding is based on sound scientific evidence. A radical transformation in embryonic life does in fact occur with implantation and the appearance of the “primitive streak” or body axis that will form the central nervous system. From this point on, twinning is no longer possible, cellular totipotency is lost, and “wastage” is reduced to occasional miscarriages.

If this view of the matter is correct, then we can have little or no ethical objection to the manipulation of embryos, created for purposes of in vitro fertilization (IVF) or stem-cell research. Presently there are hundreds of thousands of embryos throughout the world that have been produced this way. In IVF procedures, these spare embryos are usually frozen for future use, or given over to scientific research. Some are donated to couples who, for various reasons, cannot produce their own. If these embryos are not human beings, then why not use their stem cells for medical purposes, even if harvesting those cells means the embryo dies?

There are many reasons why most people today want to consider the “pre-embryo” to be less than human: a mere substratum of human life, but not life itself. On the one hand, it allows unfettered research on embryos for reproductive and therapeutic purposes, including cloning. It also allows victims of rape and incest to take whatever measures might be necessary to guard against pregnancy, with no moral consequences (that is, expelling a “pre-embryo” would not count as an abortion).

Most Orthodox, together with other pro-life people, reject the notion of delayed animation and hold that human life begins with fertilization. I have argued this position myself and remain convinced that it is correct: that full human existence—both genetic and developmental individuality—is given with syngamy, the fusion of the nuclei of the parental gametes.

Yet by defending this position, we also set up a major obstacle to research that could lead to the development of medicines and other therapies that could potentially lead to the cure of neurological and other diseases (Parkinson’s, Alzheimer’s, etc.). Even though adult stem cells hold extraordinary potential, embryonic stem cells are easier and cheaper to harvest. Does God call us to oppose this potentially life-saving and life-enhancing research? Or is our opposition simply a replay of the Church’s response to the Copernican revolution: a well-meaning but misinformed and misguided reaction against what science has discovered about the way God governs the universe?

From both a theological and a scientific point of view, the real question is not: “When does human life begin?” The gametes themselves are alive; thus the question is a false one, since it implies that there is no “life” prior to the fusion of the nuclei of sperm and ovum. Human life is a continuum, from generation to generation, from the creation of the First Adam until the coming again of the Last Adam.

The question we really need to address is: “At what point in the continuum that leads from the union of gametes, through implantation and gastrulation, does God bestow on the biological entity we call the embryo the physiological and moral status of human being?” Is it at fertilization or at implantation? This is the decidedly larger question. It is another way of asking just when God endows this new creation with the Divine Image, which implies “personhood.”

With this in mind, Orthodox theologians and medical professionals need to explore in depth both the theological and biological justification for the view that life actually begins with fertilization, and to do so in concert with specialists in embryology and fetal development. We need to explore together what God is disclosing to us concerning the mystery of life itself, particularly at its initial stage. In a world marred by terrorism, poverty and a general disregard for the sacredness of human life, as well as by widespread but potentially curable disease, there is hardly a more urgent question.