Augustine writes,
And therefore the following question may be very carefully inquired into and discussed by learned men, though I do not know whether it is in man's power to resolve it: At what time the infant begins to live in the womb: whether life exists in a latent form before it manifests itself in the motions of the living being.
Augustine of Hippo, The Enchiridion, 85.
I think Augustine’s comments ring true today. Like Augustine I believe there is good reason for thinking a fetus (a formed conceptus) is a human being and like Augustine I oppose destroying the conceptus at any stage in pregnancy. I am also inclined to agree with Augustine that prior to formation, the best stance to adopt is agnosticism if we do not know when the human being begins to exist;
I have argued for this elsewhere.
Madeleine asked Alexander Pruss to either help her understand or overcome
an argument advanced by Don Marquis that had given rise to my agnosticism regarding the point at which a human being comes into existence (human being is defined as an organism, the killing of which constitutes homicide).
My agnosticism is based on three things. The first is that I know of no reason for thinking an embryo is a human being at the time of conception. The second is that two arguments against this conclusion lead me to wonder if we can know this. The first is the twinning argument. The second is Don Marquis recent track-forward argument.
Pruss, in his post, only addresses the twinning argument. Having read Pruss’s argument I think that he and I are in fundamental agreement; moreover, I think he provides reasons for accepting an agnostic position, at least with regard to identical twins.
First, a brief summary of the twinning argument is necessary to give my readers some clarity as to what we are talking about.
Prior to the time when an embryo receives a primitive streak, the group of cells which indicate the basic body plan of the embryo, an embryo can twin. Occasionally monozygotic twinning occurs and a single embryo splits to form two or more separate embryos. Many Theologians and Philosophers have argued that this fact provides strong evidence that human beings do not come into existence prior to 14 days post conception.
The argument goes as follows. Suppose a human being comes into existence at conception, let’s call this embryo Bob. Bob symmetrically splits into two forming two embryos, embryo A and embryo B. The question arises, what happened to Bob?
There are only four possibilities.
(a) Bob ceased to exist and two new individual human beings come into existence at twinning;
(b) Bob continued as embryo A and embryo B came into existence at twinning;
(c) Bob continues as embryo B and embryo A came into existence at twinning;
(d) Bob is identical with both embryo A and embryo B.
The objector argues that each of these options is acceptable.
Pruss gives two main responses to this argument. The first is to deny that all of the options (a) (b) (c) and (d) are all unacceptable. The second is to call into question whether symmetric twinning actually occurs.
Are (a) (b) (c) and (d) all Unacceptable Options?Pruss does not argue for the acceptability of (d) and for good reason, (d) leads to a straightforward contradiction due to the transitivity of identity. According to the transitivity of identity, if an object
x is identical to another object
y and
y is identical to
x then
x is identical
z.
In (d) embryo A is identical with Bob, Bob is also identical with embryo B, hence by transitivity of identity, Embryo A should be the same organism as embryo B but clearly is not; as I noted, two separate embryos came into existence at twinning and two separate organisms cannot be the same organism.
As I stated, Pruss does not address this but he does defends the possibility of (a) (b) and (c).
Let’s turn first to (a); Pruss here suggests that this option is “not absurd” and gives an example of an amoeba; Pruss notes that when an amoeba splits into two we normally think the original one is destroyed and two new ones come into existence. So when the conceptus twins, the original one is destroyed and two new organisms come into existence.
Jeff McMahan and Peter Singer have offered a response to this line of argument. McMahan suggests adopting (a) “is an embarrassment” for anyone who opposes abortion on the grounds that life begins at conception because they are committed to the claim that “it’s a terrible loss when one of us dies in utero;” hence, anyone who thinks hominisation (the coming into existence of a human being) occurs at conception is committed to viewing monozygotic twinning as bad and as tragic as the death of a newborn infant due to the demise of the original conceptus.
Now I am not convinced by this line of reasoning entirely; if a newborn split into two and two new, genetically identical, infants were formed, it is not clear to me that we would consider this occurrence tragic, our attitudes to infants notwithstanding.
Similarly, with Pruss’ brain splitting example, I don’t think that if we conducted a brain splitting operation on a human being and placed the two hemispheres of the brain into two genetically identical bodies we would not consider this to be on par with homicide, despite the fact that we admit that an adult human is human.
Now, if cases like this happened we would be genuinely perplexed as these cases are extremely strange and bizarre, if they could happen we would end up with two beings that do not differ, either psychologically or physiologically, from the being of origin. So I agree with Pruss that this situation is possible and is not clearly or obviously unacceptable.
However, I find it interesting that while Pruss defends this option as acceptable he backs away from endorsing it; he states that “if
x in fact is going to symmetrically split in the near future,
then maybe x is not identical with any far-future entity”[
Emphasis added] he then refers the reader to his discussion of the other two cases. I think he is correct to do this; to show that an option is not false is not to show there are any reasons for thinking it is true.
Turning now to (b) and (c); the standard argument against adopting either claim is that to do so is arbitrary, one cannot provide any reason for identifying Bob with embryo A that is not also a reason for identifying Bob with embryo B. Pruss response is to argue
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.
Now on the face of it this does not appear to address the objection; the objector argues that one can never be rational in affirming that (b) is the case without also affirming (c). Pruss provides no reason for saying you can. His position is simply that either option remains possible.
I think something important can be ascertained from Pruss’ objection here and that is that the objector does not show; that either (b) or (c) are false. At best one can only show that that we cannot affirm either option nor can we deny either option has occurred. What the objector tells us here is that we cannot know at this stage.
It we look at Pruss’ response then it seems what he tells us is that when we ask the question regarding a set of monozygotic twins, did they come into existence at conception? we do not know. It is possible they did not both come into existence when twinning occurred and it is possible that one of the two began at conception though we do not know whether this is the case and even if we did, we don’t know which one of the two was prior.
Does Symmetric Twinning Occur?Similar conclusions apply to the other main argument Pruss provides against the twinning argument. He writes,
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.
Here Pruss argues that we do not know whether symmetrical twinning actually occurs and he argues that in the absence of any reason for denying that an embryo is human we should treat it as though it is. Now I don’t deny the first premise, all it does is again point out that when we are dealing with monozgotic twins, we do not know whether either or both came into existence at conception, as we do not know whether twinning is symmetric, where the above puzzles arise, or asymmetric, whereas Pruss argues they do not.
Pruss goes on to argue that when we don’t know we should treat the embryo as though it has a right to life. While I do not endorse this claim as it is phrased,
I argued for a similar claim in my post; I argued that in cases where we do not know if an embryo is a human being it would be reckless and hence, gravely wrong to kill it because it might be.
So in conclusion, I think that the twinning argument should give us pause about claiming that human beings come into existence at conception. We do not know whether twinning is symmetric or asymmetric. If it is the latter, we do not know whether anyone who is a monozygotic twin came into existence or conception or not. Either option is a possibility but we do not have the information to know which is option is correct.
RELATED POSTS:
Some Thoughts on Human Embryonic Stem-cell Research
Is Abortion Liberal? Part 1
Is Abortion Liberal? Part 2
Sentience Part 1
Sentience Part 2
Viability
Abortion and Brain Death: A Response to Farrar
Abortion and Capital Punishment: No Contradiction
Imposing You Beliefs Onto Others: A Defence
Published: Boonin's Defense of the Sentience Criteria - A Critique
Published: Abortion and Capital Punishment - No Contradiction
March was a busy month for us; we had dipped in output through December and January following my surgery, and February was kind of the acceleration month where we regained speed, but this month was as close to top gear as we can realistically get given we have 4 kids, I am permanently injured, we are studying and working, etc.
Hat tip: 
