Tuesday, March 17, 2009

Early embryos

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:

  1. Early embryos can split in two.
  2. Something that can split in two lacks a definite identity.
  3. Something that lacks a definite identity lacks a right to life.
  4. 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:

  1. Early embryos can symmetrically split into two entities of the same kind as themselves.
This premise, however, is ambiguous. To see that, consider the following argument: "Human beings can lactate; only female mammals can lactate; therefore, human beings are female mammals." The issue is that phrases like "Human beings can" and "Early embryos can" are ambiguous between a "some" and an "all" reading. Let's first try the "some" reading. Then the claim is that some early embryos have a capability for the right kind of symmetric splitting. But then the rest of the argument only leads to the conclusion that those early embryos that have a capability for splitting lack a definite identity and hence lack a right to life. One might try to paper over the difficulty by strengthening (2) to:
  1. Anything of the same kind as an entity that can symmetrically split into two entities of the same kind lacks a definite identity
and adding the auxiliary premise:
  1. All early embryos are of the same kind.
However, it is not clear what argument can be given for (7) if one thinks that the capability for splitting is of such great importance as the defender of this argument thinks. So I think this is a non-starter.

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:

  1. Every normal early embryo can symmetrically split into two entities of the same kind as itself.
  2. Something that can split into two entities of the same kind as itself lacks a definite identity.
  3. Something that lacks a definite identity lacks a right to life.
  4. 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:

  1. 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.
  2. Options (a)-(d) are absurd.
  3. Therefore, x lacks a definite identity.
But there are several problems with this form of argument. First of all, there is a serious technical problem. The argument as it stands only shows that those early embryos that in fact are going to split are lacking in a definite identity. But that is only a very small minority of early embryos, and so the argument at most establishes that some very small minority of early embryos lacks a right to life. To get around this, one needs to add something like the following premise:
  1. 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.
Now (with a bit of modal work) we can probably show that (9) follows from (15) and a version of the subargument (12)-(14).

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:

  1. 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.
But I think (16) is clearly false. If x in fact is going to symmetrically split in the near future, then maybe x is not identical with any far-future entity (but see my discussion of (12a) and (12b), above). But the mere capability of such splitting is surely irrelevant. Imagine Fred, an amoeba-like critter that every day, at noon, has a 2% chance of splitting symmetrically. Suppose that Fred in fact hasn't split during the past week (quite likely). Then Fred is the very same entity that he was a week ago. If he were to have split, we would perhaps be uncertain as to what we should say about his identity. But if he hasn't split, surely we should say that we have been dealing all along with the same entity. The mere possibility of symmetric splitting is not a threat to diachronic identity.


Madeleine said...

Thankyou :-)

Marquis also applies the argument to the early cell divisions where a singular cell organism splits into two post-conception.

Do you think your argument applies to this phenomena as well?

Alexander R Pruss said...

I think that's a different issue. I simply think the two-cell organism is the same organism as the one-cell organism.

Madeleine said...

I think your argument is very good. It encapsulates the intuitive threads of a response I had in my mind but, not being philosophically trained, lacked the ability to formulate and articulate. I only just managed to follow your argument so I could never have written it myself!

I have linked to it from our site as several people were following the discussion on it and of course linking to it forces Matt to thoroughly read and address it - he is very busy so so far had only managed a skim read ;-)

Anonymous said...

Very good summary of the issue. The gist of it was what I was thinking too (in the discussion Madeleine referred to) but you've explained it in great detail. I feel the amoeba is the best illustration.

Strangely, in general more atheists than Christians appear to believe the conceived embryo is not human. But if there is no soul, this idea is completely false.

It is only if a soul exists that the twinning argument could be seen to have some merit - and you have effectively shot that one to pieces too. As we have no idea when the soul is imparted, you cannot argue this issue based on the soul because you can never prove your assumptions.

Alexander R Pruss said...

It's probably easiest to argue for the pro-life position if one is a hylomorphist or a materialist. The substance dualist has it harder, but she can at least argue that we have no right to kill something that, for all we know, might be a person.

Matt said...

Thankyou for helping my wife. I tend to agree with much of what you said. I have made some comments but as they are too lengthy to post here I have put them on my own blog.

Alexander R Pruss said...

Thanks for the careful response! I posted a response thereto.