Many From One: The Metaphysics of Human Genesis

The debate over the research use of human embryonic stem cells rages. I have little new to say about it. But I would like to correct one nearly ubiquitous mistake. It is that a human being begins to exist when sperm fertilizes ovum. (In what follows, when I speak of sperm, ovum and zygote, I mean the human variety.)

Of course I do not dispute that the fertilized ovum, i.e. the zygote, is alive. Nor do I dispute that it is human. But it is not yet the human being that will come to exist.

How can it be human and not a human being? It is human but not a human being in precisely the sense that a sperm or an ovum is human but not a human being. (For simplicity, consider only the example of a sperm cell.) A sperm is human in the sense that it originates in a human male. It is thus human and not, say, bovine or canine. But of course it not a human being.

Note that the indefinite article 'a' is crucial here. A sperm is human but is not a human. (Of course a human is human. But a thing might be human and not a human.)

What I've said so far is beyond dispute. If you think it false, or do not understand, give it another go. Do not continue on until you understand.

Now begins the metaphysics. I've said that a zygote is human but not a human being, and I've explained what I mean by this. But I've not yet given my reason. The reason takes us into the metaphysics of identity.

When the zygote divides, it gives rise to a pair of new cells. Does the zygote survive its division? If it does, it is either one or the other of the pair of cells to which it gives rise. (It cannot be both, for one thing cannot become two things.) But since the two cells to which it gives rise are exactly similar, we can have no more reason to say that the zygote becomes this one than that it becomes that one. Thus neither of the pair of child cells is the proper successor to the parent zygote cell, i.e. neither is identical to the parent. Conclusion: when the zygote divides, it ceases to exist.

Note that a human zygote is in this regard precisely similar to all cells that undergo division. When an amoeba divides, it ceases to exist. When a bacterium divides, it ceases to exist. Cell division is, in all cases, at once both destructive and generative. The parent cell ceases to exist. The child cells begin to exist.

Now, assume for the sake of reductio ad absurdum that a zygote is already a human being is not a mere precursor thereof. (Reductio ad absurdum is a form of argument in which a certain assumption is show false by the deduction of an absurdity from it). As argued, when the zygote divides, it ceases to exist. Thus when the zygote divides, the human being that by assumption it was ceases to exist. Of course if this were so, we must say at some point in time either at or after zygotic division, a new human being comes to exist, for of course pregnancy does end in the birth of a human being.

This is absurd. Pregnancy does not progress through the creation of one human being, its destruction, and the creation of a new. Rather there is only ever one human being within the womb. Thus the assumption with which be began must be false. It must be false that a zygote is already a human being.

This leaves us with the question of just when a human being does in fact begin to exist. Is it when the zygote divides, or is it after? I suspect that it's not at the time of division but rather some days after. I'll return to the issue in a later post, but do note that the door has been opened for even the most ardent defender of the sanctity of human life to endorse embryonic stem cell research.