A single-celled zygote (on day one of fetal development) is the precursor of a baby and the precursor of the placenta that will support fetal development. Thus, if we say the single-celled zygote is identical to the much later baby, we'd have equal reason to say the zygote is identical to the later placenta. But then, because of the transitivity of identity, we'd have to say baby and placenta are identical. So each of us was once a placenta! But no--that's surely absurd. So it cannot be true after all that the single-celled zygote is identical to the later baby (or placenta). The earliest that an individual (like you or me) comes into existence is when sufficient differentiation has taken place so that an entity exists that's the precursor of a baby and not the placenta. That time is at least several days after conception--when a blastocyst has become differentiated from the rest of the cellular material.
The logic here certainly makes sense. If a certain block of wood is a precursor of both a toy duck and a toy dog, it's not true that the duck is the same entity as the block of wood. You can't assert that identity, since there's equal reason to say the dog is the block of wood, and then you're faced with the absurd conclusion that the duck is the dog.
If it worked, the placenta argument would have some very important real-world implications, like forcing Catholic hospitals to change their policies on the morning-after pill for rape victims. They would have to admit that, for the first few days of development, the zygote is an entity in the same category as an egg or a sperm--a precursor of a baby but not the same entity as any future baby. Catholics will want to resists mightily, of course. They might say ... what?
What you might say is that a placenta is just a part of a fetus--essentially an organ, but one that happens to be (a) external and (b) temporary. A zygote is a precursor of a whole baby, but (of course!) also the precursor of the baby's parts. If we said the zygote is identical to a certain baby, we certainly wouldn't have equal reason to say the zygote is identical to the baby's liver, or heart...or whatever. The part-whole relationship between individual organs and whole baby blocks those identities. Likewise, arguably, for the placenta. It's just another organ, you might say, so a part (though external and temporary).
If we gave that response, would we just be making things up? Does it really make sense to think of the placenta as a part of a fetus? Is it more aptly thought of as a part of the mother? What is a placenta, really? It's curious that such an arcane biological-metaphysical question could have any bearing at all on what hospitals should permit rape victims to do. Surely there are many far more important ethical considerations. I certainly think so, so I'm talking about this issue merely "ad hominem" (in the technical sense, not the "street" sense), i.e. as relevant just to those who do oppose abortion on grounds that a baby starts to exist at conception.
If a placenta is a separate entity from a fetus, and not a fetal part, then thoughts about zygotes, placentas, and identity could show, quite decisively, that the very earliest conceivable start to any individual human being's existence is a little bit later--at least a few days after conception.
Interesting. So first, let me get this out of the way, I don't think the placenta and the fetus are identical. But in light of what I'm reading right now, (You know what it is Jean) let me try to explicate it from the Catholic perspective the best I can (assuming Camosy is doing a good job of representing the Catholic position, and I'm doing a good job representing him).
So the potential of the fetus determines the personhood of the fetus. Since the fertilized blastocyst has the potential, and the blastocyst is identical with the fetus, and the blastocyst is identical with the placenta, its really hard to deny that the placenta isn't the fetus. So yes... we were each placenta... Just as much as we were each hair.
The problem is that hair isn't part of the support structure that fosters the potential human. But placenta, most certainly is. So the placenta is as valuable as the fetus, so long as the placenta is playing a role in the potential of the fetus. But at some stage in the development of the fetus, it will no longer need the placenta. So it will no longer be partly fostering the potential of the fetus, so it is no longer morally relevant.
Lets look at it another way. Imagine that an elderly man has a cane that he needs in order to walk, and be mobile. Without it, he will DIE. HE can't reach food, or meet his own needs. Is the cane him? No. But would it be wrong to take it away from him, assuming no proportionate reason to take away the cane (e.g. it might ease some other form of suffering a la euthanasia)? It seems like it would be wrong.
Okay that said... I think its best to think of it as a fetal part... But a part that it eventually outgrows and is shed. maybe like the shell of a chicken egg, or baby teeth. Generally, we don't look at our hair or our teeth and think, "oh look! Me!" Its just an odd way of speaking. If I had my arm amputated, I wouldn't ask where that part of me was... If my brain was removed from my body I wouldn't ask "Where did the rest of me go?"
Not sure if I'm following. Sounds like I should read Camosy.
Sure--if you think fetuses ought to be protected, you ought to protect placentas too--like you'd protect the old man's cane. But the real question is when you and I come into existence--as zygotes or later? The problem with saying "as zygotes" is that zygotes are package deals. Inside the package you have precursors of two different things--fetus and placenta. That stops the zygote from being identical to the fetus (or identical to the placenta). The only way around this (I think) is to say the the fetus and placenta aren't actually two different things, but the fetus is a whole of which the placenta is a part. But I find that not at all obvious. Saying the placenta is part of the fetus is about as plausible as saying an eggshell is part of the chick inside. At the very least, it seems like there are other equally good ways to think about it.
This reminds me of the Tibbles problem. Tibbles the cat is a normal cat, and Tibbs is a cat without a tail, that is identical in all other respects to Tibbles. Tibbles loses his tail in an accident. Now Tibbles is identical with Tibbs. Is there any non-anti-intuitive way of resolving this problem? Does Tibbs always exist? Did Tibbles cease to exist? Does Tibbs have no history in common with Tibbles? Are there two cats that exist at all times?
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