First, there's biological life, something being engaged in the biological processes that define life in a biological sense.
It is very, very obvious that biologically human zygotes and embryos and fetuses are biologically alive: they came from eggs and sperm which were biologically alive; they are engaged in the processes mentioned on page 1 of a biology textbook.
But this obvious fact that biologically human fetuses are biologically alive isn't very important because of this: just because something is biologically alive, that doesn't mean it's wrong to kill it. E.g., mold and plants are biologically alive, but they aren't wrong to kill. Other counterexamples make the point. (Now, the point is not that human fetuses are comparable to any living thing; the point is to engage the exact premise that completes the reasoning as given).
So here's the problem: if someone thinks that proving the obvious—that biologically human fetuses (we aren't talking about kitten or puppy fetuses, right?) are biologically alive—proves that abortion is wrong, that is mistaken: it's a bad argument.
I think this explains the negative reactions that Jacobs got: people thought, "Oh, he's going to take my answer and use it to argue for conclusions that it really doesn't support." And they were right about that. (Right?).
So what else can "When does life begin?" mean? In particular, what can "When does human life begin?" mean?
You can get at that by thinking about the question "When does a human's life end?"
Most people recognize that this is a complex question because of examples like a permanent coma or permanent vegetative states or major, major brain damage. In these cases, someone's body may be alive, but their brain is dead: so we often think that their life has ended, even though their body is biologically alive.
Why has their life ended (even though their body is biologically alive)?
So back to the question: when does "life begin" for us, and “life” in the morally significant sense, or "biographically human life"? When consciousness begins. And this is a different answer than the biological answer, in part because it's a different question: it's not just about biology; it's about us and what we really are: although we are very much related to our bodies, we are not our bodies.
So, this problem all arises from asking an ambiguous question and not clarifying the options for what the question might mean: in other words, not engaging in a core task of critical thinking. Had that been done, the answers here, from biologists and anyone else, likely have been quite different, as would have been the tones of their reaction!
- "When does life begin?" and "Are fetuses human?": Two bad 'scientific' questions to ask about abortion
- Would around 70% of people * deny * that "human life begins at conception"?
- "When does life begin? Well, when does life end?"
- On Saying What You Mean: the "Principle of Charity" and the "Principle of Clarity"
- Does "life" begin at conception? Biological versus "biographical" life
- Are fetuses "human beings"? Biological versus psychological definitions
- Are you part of a cult about abortion, or anything else?
- Updating the question to "when does biologically human life begin?" or even "when does a biologically human organism begin?" doesn't change the discussion: the points above still apply.
- Further comment: Jacobs write this:
If a fetus is not a human, then abortion restrictions stop women from having a basic, harmless medical procedure.If a fetus is a human, then each abortion kills a human and is a presumptively punishable crime without an affirmative legal defense.
About the second claim, each fetuses is obviously "a human" in the biological sense and abortion kills beings that are biologically human: every thoughtful pro-choice person recognizes that (any who are not are confused). What they deny is that fetuses are "human" in the sense of having what they consider human characteristics, like consciousness, feelings, awareness, and so on, and they think that those types of characteristics are what make killing someone wrong. So this statement suggests a misunderstanding of what people actually think about about these issues.
About the first claim, again, of course fetuses are biologically human, but they are not "human" in the sense of having what they consider human characteristics, like consciousness, feelings, awareness, and so on. But that doesn't automatically mean that abortion is not wrong either: e.g., the most famous and important philosophical argument against abortion, from Don Marquis, denies that fetuses are "human" in this sense. So this claim is false: even if fetuses aren't human in this sense, they could be wrong to kill nevertheless.