What do you think a living organism is?
Yes, but importantly each twin is not the same individual as the other and so they cannot both be the same individual as the zygote. Therefore either just one of them is the same individual as the zygote (special pleading) or neither is.
The fact that they can "trace their history and existence" to the zygote does not entail that they and the zygote are the same individual.
A eukaryotic cell containing 24 distinct chromosomes.
I’d say that the embryo and the placenta are each their own thing, albeit connected by the umbilical cord. I wouldn’t consider any of these three things to individually be “the human”, and nor would I consider all three of them to collectively be “the human”.
But we can even drop consideration of “the human” here and just consider the embryo. A zygote develops into a blastocyst, and then some of its cells develop into a placenta and some into an embryo.
To say that the placenta is part of the embryo rather than that the embryo is part of the placenta is special pleading.
What does it mean to be a member of the human species?
Do you have an aversion to the term zygote?
Now you are. Morality is strictly to do with how we treat one another. A Zygote is not a 'one another'. This is probably the only intuition of Banno's I think needs no defense. This just, as noted, leads to some hefty bullet-biting.
At what point the zygote becomes a 'person', or variably 'baby', 'a human' etc... etc... These are the 'facts' on which most people's positions rely(i have excluded those absolutist positions that are doctrinaire rather than reasoned) and they aren't stable or lets say 'complete' enough to objectively inform us of anything within that grey area as to why we would place the flag 'there'. Yes, we know a lot about zygotes and their development, but which way-point would you choose? It sounds like for you it's conception. Others might be implantation, heartbeat, viability, pain reception among others. But none of these are hard-and-fast in terms of telling us when a 'person' comes into being (or, when that might be morally relevant). I can only really understand taking conception to be the salient point if one is to be, lets say, overly cautious, because of the above indeterminacies. If you're not copping to that, I'm unsure how to make sense of it. But this doesn't seem to me a moral question, anyway. It's similar to saying "well, I can't figure out the precise moral facts, so I'll give it a wide berth". I can't see a real problem in that, other than tryig to make others assent (which you're not doing, so that's fine).
We wouldn't know, or care. That's not a moral consideration.
None of this is the case, and the quote you responded to points each out. There is no incoherence. There's just potentially uncomfortable bullet biting.
THe 'vagueness' of the terms doesn't exist. The facts are vague. The terms refer to them. This is no point at which a zygote 'becomes a person'. It does not exist. It occurs somewhere in the grey area and any position has to choose an arbitrary point here if that's what the view is based on.
(though, its very, very much worth noting that 'arbitrary' is not apt here. There are reasons which very much restrict what's acceptable on most views except absolutists ones (i.e killing an infant is also fine, or there is no form of contraception which is acceptable).
Well, ethics is about what we do. And I'm off to an art exhibit and lunch with friends.
Not something that can be done with a zygote.
As I mentioned in an earlier post, there is no single point, much like with the Sorites paradox. It's acceptable when it's a zygote or blastocyst or embryo, not acceptable when it's due to be delivered in a day, and in between there's a large grey and ambiguous area as it develops more and more into a human like us.
There is much more to an organism than its genetic makeup. There are very real, significant, and obvious biological differences between myself and a zygote. Your decision to only consider an organism's genetic makeup is not less arbitrary than my decision to also consider these other important aspects of an organism's being. But I do think that your claim that only an organism's genetic makeup has moral relevance is an absurd one.
So why does anything with our genetic makeup deserve to live?
Yet these words need shared meaning between individuals for this to be achieved. It need not be ectoplasm, but it needs an inter-subjectivity whereby the words mean roughly similar things. Thus, uniqueness itself is something one must understand to understand others are unique. But then, there is a sameness already built into the language meaning.
And thus, what is this shared "space"? Well, it isn't location, as you say. But there is a sort of type of consciousness that humans share.
So what distinguishes a human organism with human DNA and a non-human organism with human DNA, and why is the distinction the measure of whether or not it is wrong to kill it?
And to be a member of the species homo sapiens is to have the appropriate ("human") DNA? So when you say that it is wrong to kill a foetus because it is human you are simply saying that it is wrong to kill a foetus because it has human DNA.
I fail to see how you get from "the foetus has human DNA" to "therefore it is wrong to kill a foetus".
Yes. As related to my reply to Hanover above, what a human is depends on how we use the word "human", and how we use the word "human" is a contingent fact about the English language, open to change. If we use the word "human" to refer to anything with human DNA then embryos are human. If we use the word "human" only to refer to sufficiently developed organisms with human DNA then embryos are not human. It is a mistake to commit to some kind of essentialist view of being human such that we can be wrong in (not) using the word "human" to refer to embryos.
And whether or not it is morally acceptable to kill an embryo does not depend on whether or not it is conventional in the English language for the word "human" to refer also to embryos.
We need to look to more concrete facts. These concrete facts are biological, neurological, and psychological. Simply having human DNA is not sufficient biological grounds to entail that the thing "deserves" to live. Whereas being able to think and feel and so on is sufficient biological, neurological, and psychological grounds.
What are these "same reasons"?
Because I would say that it is wrong to kill other humans because it is wrong to kill humans with thoughts and feelings and wants. Embryos and (early stage) foetuses don't have thoughts or feelings or wants. They are more like the brain dead living on life support.
a) "X is a human" means "X has human DNA"
b) It is never acceptable to kill a human
c) Therefore, it is never acceptable to kill something with human DNA
The biggest and most relevant difference is that a baby is no longer being carried in the womb of its mother, and so for the most part the mother's bodily rights are no longer an issue.
Another significant difference is that the thalamocortical connections that are required for consciousness do not develop until ~26 weeks of pregnancy.
You've asserted that it is wrong to kill anything with human DNA (except in self-defence, etc.). You haven't justified this.
It was an embryo, but now isn't. There is a very real biological difference between a baby and an embryo. That very real biological difference has moral relevance and is why it is wrong to kill a baby but not wrong to kill an embryo.
So are you now saying that it isn't wrong to kill a human embryo? Or are you refusing to show me what makes killing a human embryo wrong? This is why you are special pleading; you demand that we show you what makes something a person but refusing to show us what makes killing a human embryo wrong.
And if I ask you to show me what makes killing a human embryo wrong?
There is a very real biological difference between an embryo and a baby. They might share the same kind of DNA, but there is much more to an organism than its DNA.
Echarmion asked "is this supposed to mean that there's no evidence for personhood?"
You responded with "I understand, and have no problem with either term in common usage, but if I were to ask you to point to whatever it is you're referring to you would invariably point to your body, which has existed and grown since conception. That's what I'm hung up on."
I am simply explaining that being (or not being) able to point to something has no bearing on whether or not someone is a person, just as being (or not being) able to point to something has no bearing on whether or not something is wrong.
I don't understand your reply. You say there is no means to determine personhood, yet (if I follow you correctly) you agree that a country's legal system has to make that decision.