It is often argued that the early (pre-implantation, human) embryo does not have a right to life because it is capable of twinning. The question is important, because if such an embryo does have a right to life, then embryo-destructive research (such as stem cell extraction) at this stage is wrong, and forms of birth control that can prevent implantation (e.g., the IUD, and perhaps hormonal contraception) are problematic.
I am going to try to reconstruct the best argument for this position, and then shoot it down. As an initial attempt, consider this:
- Early embryos can split in two.
- Something that can split in two lacks a definite identity.
- Something that lacks a definite identity lacks a right to life.
- Therefore, early embryos lack a right to life.
This argument is unsound. Each of us can split in two, for instance if we find ourselves victims of the guillotine. Yet we have a definite identity. So (2) is false. (It wouldn't help to add "naturally" to "split in two". First, we don't know that the embryo's splitting is "natural"—it might be an accident of some sort. Second, we can easily imagine critters that have a definite identity, but die by breaking up into two pieces.)
To fix the argument, we need to improve on premise (1) by saying something more about how early embryos can split in two. They do simply split in two: they twin. One way to formulate this is by saying that an embryo can split into two "entities" (I will use the term "entity" very widely, to include non-substances, heaps, etc.) of the same kind as it. But that won't be enough. For suppose that George is a member of a species that reproduces by growing a new member of the species as a bud on the shoulder. Then George can twin, but the ability to bud in this way is no threat to his definite identity or his right to life (if it's a species of persons). The issue, rather, seems to be with symmetric splitting.
So now our first premise is:
- Early embryos can symmetrically split into two entities of the same kind as themselves.
- Anything of the same kind as an entity that can symmetrically split into two entities of the same kind lacks a definite identity
- All early embryos are of the same kind.
Thus, the quantification in our initial premise needs to be over all early embryos. Or, maybe, all "normal" early embryos, allowing for the possibility that some early embryos might suffer from a splitting-disability. The argument now is:
- Every normal early embryo can symmetrically split into two entities of the same kind as itself.
- Something that can split into two entities of the same kind as itself lacks a definite identity.
- Something that lacks a definite identity lacks a right to life.
- Therefore, a normal early embryo lacks a right to life.
Indeed, (11) follows logically from (8)-(10). So the question is whether (8)-(10) are true.
Now, a glaring problem is that we do not at present know (8) to be true. There are two parts of this problem. The first part is that, last time I checked, we did not actually know that embryonic splitting is in fact symmetric. If it turns out that embryonic splitting proceeds by budding, the argument falls flat. Thus, the argument rests on an empirical hypothesis which is merely speculative. This is a problem: obviously, if the case for the lack of a right to life on the part of some organism is based on a merely speculative hypothesis, we should treat the organism as if it had a right to life until that speculative hypothesis is checked.
The second part of the problem with (8) is that we do not in fact know that all normal early embryos have the capability for splitting. The alternative view is that only some early embryos have a special characteristic in virtue of which they are capable of splitting (and there is no particular reason to think that this subclass of early embryos exhausts all the normal ones). As far as I know, we do not at present have enough empirical information to decide this issue. So, once again, (8) is up in the air empirically, and if this is what the case against the right to life of an early embryo is based on, we should treat the early embryo as if it had a right to life.
One might think that (8) could be defended by saying that even if naturally splitting isn't symmetric, or if only some early embryos can naturally split, still all early embryos could be surgically split. Maybe. But then (9) must be understood in a way that includes artificial splitting as well. And I think (9) understood in this way, conjoined with (10), is implausible. For it seems likely that one day it will be possible to destroy all of your body outside of your brain, so that you would be reduced to a functioning brain in a vat. If you were thus reduced to a functioning brain in a vat (say, as a radical treatment for an otherwise untreatable cancer—a rest-of-body amputation), you would surely still have a right to life. But a brain in a vat could, probably, be artificially split into two hemispheres in their own separate vats. And the split versions would seem to be the same kind of entity at the original, namely persons. So this would be a symmetric splitting of a person into two persons. But the mere possibility of such splitting surely neither threatens your identity nor removes your right to life, whether it is remote (as it is now, when you are not yet a brain in a vat) or near (as it would be were you to have the misfortune of being a brain in a vat).
So if (8) is understood to be only about natural splitting, our empirical knowledge does not give us (8). And if (8) is understood to be about artificial splitting, we should deny the conjunction of (9) and (10) under the appropriate interpretation of (9).
But let us suppose, for the sake of argument, that in fact (8) is true, and even true as regards natural splitting. Why should we believe (9)? It is tempting to say something like this:
- If x symmetrically splits into y and z which are of the same kind as x, then either: (a) x=y and not x=z; or (b) x=z and not x=y; or (c) x=y=z; or (d) x ceases to exist and y and z are new entities; or (e) x lacks a definite identity.
- Options (a)-(d) are absurd.
- Therefore, x lacks a definite identity.
- If x is capable of doing something such that, were it to do it, it would lack a definite identity, then x lacks a definite identity.
But is (15) plausible? Suppose I am able to split my brain in half, through programming a robot to do it, or maybe through a feat of auto-neurosurgery. Perhaps a split brain patient lacks a definite identity. But even if it were true that a split brain patient lacks a definite identity, it would not follow that my capability of turning myself into a split brain patient makes me already lack a definite identity. So I think (15) is very much problematic.
Moreover, I reject (13). First of all, if dualism is true, then the kind of symmetry we are dealing with is only physical symmetry. It is quite possible that the physical facts are symmetric but the facts about the soul are asymmetric. Thus, (a) or (b) might be true. There might be some law specifying which of y and z gets x's soul, either in terms of some minor asymmetry (nobody thinks the asymmetry is total, with each half having the exact same number of molecules, in exactly the same positions) or stochastically (maybe it's random where the soul goes), with the other output entity getting a new soul. Or it might be that God decides where x's soul goes. So if dualism is true, (a) and (b) are not absurd.
Moreover, whether or not dualism is true, (d) is not absurd. It seems very plausible that this is the right thing to say about an amoeba's splitting: the old amoeba perishes in the act of reproducing into two new ones. If I cut a sculpture in half, symmetrically, I have very plausibly made two new sculptures out of the one old one, which perished in the cutting. And, of course, the fact that something has a capability of perishing does not imply it lacks a definite identity, since all the non-human organisms on earth have a capability of perishing.
In fact, the case of the amoeba shows directly that we should deny (9). An amoeba has the capability of splitting into two amoebae. But surely it exhibits a perfectly definite identity at least when it is not actually splitting. If the amoeba in my microscope slide hadn't split over the last 12 hours, and hasn't yet started splitting, then I now have the same amoeba I had 12 hours ago. That seems perfectly definite.
Moreover, it would be very surprising if there couldn't be intelligent aliens who reproduce like amoebae. And if there were such aliens, they would be a counterexample to the conjunction of (9) and (10): for they would be capable of symmetric splitting, but would, nonetheless, have a right to life.
Perhaps, though, the conclusion of the argument should be more modest. Instead of concluding that normal early embryos lack a right to life, maybe the argument should only conclude something like this: Don Marquis' argument against abortion does not apply to normal early embryos. For, Don Marquis' argument requires an identity between an embryo or fetus and an adult, so that killing the embryo or fetus is depriving it of a future like ours. I am not sure Marquis actually requires identity here (what he says about sperms and eggs suggests that he is talking of a relation weaker than identity). But nevermind—suppose he requires identity. Then one might argue that if the early embryo is capable of splitting in the near future, then it is not identical with a future adult. More precisely:
- If x is capable of symmetrically splitting into two entities of the same kind in the near future, then x is not identical with any far-future entity.