So, I’m arguing with someone on the internet (because that is apparently what I do with my life) and I keep running across this sort of argument “Science proves that a fetus becomes human when it can survive outside the womb.” Please do not say this. First, science has proved no such thing. But more importantly, the statement itself is confused.
In common language, to be a human is to be a person, and the words are used pretty interchangeably, since everyone instinctively recognizes that to be human is to be a person “endowed by their creator with certain inalienable rights.” But when you are discussing medical ethics, the distinction between what is a human and what is a person is precisely the subject under debate, so you have to make careful distinctions.
“Human” is the species. I am a human. My cat is not a human. I did not become human; I have always been a human. If science were to prove that an unborn child can become human, you would have to demonstrate a process whereby two human parents came together, contributed a human ovum and a human sperm, and produced an inhuman embryo. If it is not human, what species can it be?
What is actually under debate is the “personhood” of the unborn. Personhood is an ethical and political category that serves two purposes: to assign to non-human organisms the rights that are normally accorded to humans, or to remove from humans the rights that they would normally have. So, for instance, an animal rights activist might argue for the personhood of dolphins, in order to accord them the rights of life and liberty. You might also argue that, if we ever found intelligent alien life, or elves, that they would be considered persons, even though they were not human. At the other end, when the US constitution was first written, Southern slaves were counted as 3/5 of a person for the purposes of the census. You can see how well that went.
So in the original statement, science has not proved that an embryo becomes human. What the person is really arguing is that an unborn child becomes a person when they can survive outside the womb. It’s a valid position to take, but again, science doesn’t prove it. Science can’t prove it, because personhood is not a scientific category. The ability of a fetus to survive outside the womb is called viability. Medical technology is constantly pushing the boundary of how early viability can be established. So all that “science” can do is reveal the historical data of how early viability has been established.
What you are left with is an unsubstantiated argument that personhood should be established according to the functionality of human organism’s lungs. This strikes me as an extremely tenuous argument.