Why should it matter?
It matters not under current law as I understand it, but it matters to me since in my view the essence of what we are is our minds, not our form. If a person is whole in the body, but there is no brain activity then there ain't nobody home. The body may continue the biological functions of life, but the person is gone.
Or we could say the "person" is floating in Mama's innards like it's supposed to be at that stage in its life. You're defining a person as something more than just a living human. Feel free to do so, but recognize that's not different from the religious person who claims that the soul enters the body at birth, therefore the unborn are not persons and may be killed up until that point. Another person could claim that only adherents of religion X are true persons, living up to their full potential. You can't really argue with that kind of thinking, because each one is defining "person" for themselves. How about if the law disregards philosophical and religious claims about "persons" and simply protects living humans? This may get fuzzier at the other end of life, but at the beginning it's quite simple.
Unadorned science tells us that the zygote is a new human individual.
Was your quotation from Wiki supposed to disprove this or just add to it? What was the point of it?
Then what of stem cells? While we do not yet have the ability to take a stem cell and cause it to grow and differentiate into a whole person, it is foreseeable that one day we WILL have that technical capacity. Is an stem cell a person? Some abstracts I've seen in recent years indicate that differentiated cells can be converted back to that undifferentiated stem cell state. Is a cluster of viable cells from my body 'me'?
What of them? A stem cell is merely one part of a whole organism. If, someday, it can be turned into an embryo, then it would be a new human organism unto itself, and would be an individual worthy of the protection of law. The same for the cluster of viable cells from your body. Of course they are not you - they are just a part of your body. They are not an entire organism unto themselves.
Then the point was viability outside the womb, until I started thinking about just what makes us different from the other animals. The child may not be viable, but the brain and mind are still developing and will continue to do so for YEARS after birth and based on my criterion, abortion at that point became abhorrent. For myself in matters physical and corporeal, reason rules. And I'm am not one to judge others in matters spiritual.
So, you'd say the embryo is not human until you can detect brain waves and until then it is no different from an animal. This is like saying that a bovine embryo does not have discernible teats, therefore it is not a mammal. The bird embryo has no feathers, therefore it is not avian. As I understand it, science classifies embryos in the same taxonomic category as the mature form. Therefore, a dog is a dog, a chicken is a chicken, and a human is a human, simply in different stages of development.