When does life begin? Two prolife philosophers disagree.

My esteemed Notre Dame colleague, John Finnis, will receive the third annual Paul Ramsey Award for Excellence in Bioethics from the Center for Bioethics and Culture (CBC), a conservative Christian think tank. Paul Ramsey (1913-88) was a pioneer in the field of bioethics. He was also one of my teachers at Princeton. I wonder whether the CBC would consider Ramsey himself suitable for the award it issues in his name? Firmly prolife, Ramsey still considered some questions--such as the status of the early human embryo--to be legitimately debatable by committed Christians. I'm not sure the CBC feels the same way. The chair of its nominating committee, C. Ben Mitchel, has said that denying that the early embryo is a human being is analogous to denying the humanity of Jews and slaves. Would Paul Ramsey agree?

I don't think so. In fact, Ramsey had serious reservations about the position that individual human life starts at fertilization--an opinion Finnis shares with the worthy previous recipients of the Ramsey Award, Germain Grisez and Edmund Pellegrino--both Catholics. In Ramsey's classic and wide-ranging essay "Abortion: A Review Article" (The Thomist, 1973), he engages in vigorous, detailed, and still-relevant debate with Grisez's Abortion: The Myths, the Realities, the Arguments (1970).

In that book, Grisez argues that individual human life begins when egg and sperm unite, creating a fertilized ovum (a zygote) with a full complement of forty-six chromosomes. That zygote then undergoes cell division, becoming an embryo. But there is a wrinkle to the argument: for about two weeks after fertilization, that embryo may split, resulting in identical twins. Less commonly, two embryos may combine, resulting in one individual. As Ramsey notes, "there is fluidity and indeterminacy in either direction during the earliest days following conception." So how do we think about the various entities involved in twinning and combination?

In the case of twinning, Grisez argues, we must think in terms of three distinct human individuals. The original embryo--let's call it A--is a human individual distinct from its parents. The twins--let's call them B and C--are human individuals distinct from each other and from the fertilized egg from which they sprang. What is the relationship among A, B, and C? Grisez explains that "we should think of the twins as the grandchildren of their putative parents, the individual that divided being the true offspring, and the identical twins of that offspring by atypical reproduction." In other words, A is the child of the parents, and B and C are the grandchildren. This is odd, since A neither died nor gave birth. Rather, A split through a form of asexual reproduction. Grisez likens the split to the way in which "two individual animals of many lower forms of life can develop by the division of a single, existing individual." In his article, Ramsey conjectures, with a note of incredulity, that Grisez must be talking about halved earthworms.

What about two embryos combining to form one? Grisez says this involves two individuals, A and B, combining to form C, who is a distinct new individual. He suggests this scenario is analogous to that of "a grafted plant." Ramsey's response: "With considerable astonishment we may ask whether any such 'individuality' is the life we should respect and protect from conception. In trying to prove too much, Grisez has proved too little of ethical import."

Analogies to earthworms and plants seemed implausible to Ramsey. So did Grisez's invitation to think of identical twins as the grandchildren of the woman who gave birth to them. Grisez's attempt to preserve the claim that individuated human life begins at fertilization sacrifices too much of what we know about human nature--both from a Christian perspective and a scientific one. After all, human beings reproduce sexually, not asexually. Humans are mortal; they die and their bodies disintegrate. They don't split neatly into two with no loss, cost, or remainder (as in twinning), nor do they merge fluidly into one another (as in combination).

Ramsey thought it plausible that an individuated human life does not begin until the possibility for twinning and combination has passed, a stage called restriction, about two weeks after fertilization. Assuming Ramsey was right, what does that mean for research on human embryos that destroys them in the process? If the embryos have not reached the stage of restriction, such research would not count as homicide, because it wouldn't involve killing a human being.

If it's not homicide, is such research morally permissible? Perhaps, given its potential benefits. But not necessarily. Ramsey was deeply suspicious of the scientific imperative to manipulate human destiny in the name of progress. He was keenly aware of the slippery slope such research puts us on. Should the research prove effective, the inevitable temptation will be to use more developed embryos and even fetuses in our research to get better results. On his view, that would be homicide.

Paul Ramsey's powerful and fearless intellect led him to differ not only from secular liberals, but also from religious conservatives. If the CBC issues an award in his name, its leaders ought to refrain from demonizing as Nazis or slaveholders those who hold positions that Ramsey himself considered defensible.