Why do pro-lifers think that embryos become precious immediately after conception? Does a switch get turned on that instantly makes the fertilized egg precious? I mean: not just precious in onlookers' eyes, but inherently precious.
What makes a person inherently precious, I think, is (dormant or active) consciousness: thoughts, feelings, memories, hopes, and awareness. Since consciousness depends on the development of the nervous system, and since it takes many months for the nervous system to mature, we can conclude that consciousness emerges gradually. Consequently, the inherent preciousness emerges gradually too.
Granted, a sleeping or comatose person has no consciousness either. But a sleeping or comatose person's consciousness is latent: if they wake up, they have memories, etc.
For a fertilized egg, there is no consciousness and also no history of consciousness (unless you believe in reincarnation). Even though all the DNA is there, the fact that there's no higher brain activity strongly implies that there's no consciousness.
Nor does the later presence of a heartbeat and of primitive neural activity imply consciousness or preciousness. What's needed is higher brain activity and the consequent self-awareness.
Now, I grant that nobody knows for sure what consciousness is -- philosophers have been speculating about the nature of consciousness for years, and scientists haven't yet tackled the issue. But it is quite clear that consciousness does not emerge full-grown immediately after conception. And since I believe in science, I have to presume that consciousness emerges gradually with the development of the nervous system.
So sure, an embryo is a growing human being. Sure, it's a potential person (as are an unfertilized egg and sperm). But it's not yet a conscious person and hence not yet inherently precious. That's the distinction.
We generally reserve the word "human" or "child" to refer to a thinking, feeling being. So calling an embryo an "unborn child" is odd, since it masks clear distinctions between an (unconscious) embryo and a (thinking, feeling) child.
Now, if you believed that a "soul" enters the embryo at conception, then I could understand that you'd likely think abortion is murder. But I doubt that pro-lifers want to depend on an essentially religious argument.
In short, pro-choicers can say: abortion isn't murder because until there's a mature nervous system, there's no conscious person, just a potential consciousness (a clump of cells). Nor is there any pre-existing (dormant) consciousness, as there'd be in the case of a sleeping or comatose person.
So, I'm suggesting the following equation: person = existing or pre-existing consciousness = mature nervous system.
Given that the development of the nervous system and consciousness is gradual, when does the embryo become conscious enough to be considered a person (a precious human being)?Arbitrary cutoffs
Some anti-abortion activists concede that the maturation of the nervous system is gradual. They acknowledge that there's no clear line (cutoff) between non-consciousness and consciousness. Therefore, they argue, it's arbitrary to say that life begins at, say, three months; far better, they argue, to play it safe and say that life begins at conception, which is non-arbitrary. In other words, anti-abortion activists say that setting a cutoff later than conception is arbitrary.
I agree that there's no precise place to draw a line, because development is gradual. However, this doesn't imply that we have to draw the line at conception or that it's completely arbitrary to draw a line later in development.
By analogy, there's no clear line between pornography and art, but some books are clearly pornographic, and some books are clearly art. Saying there's no clear line does not mean that we should say that all books are art or that all books are pornography. But for practical purposes (e.g., the law) we may need to set a somewhat arbitrary cutoff, somewhere in the middle.
The word "arbitrary" is ambiguous. It can mean "completely arbitrary" (meaningless, or random), or it can mean "partially arbitrary" (imprecise). It's the latter sense that's operative here when we're talking about embryonic development and consciousness.