Is the beginning of a human life something we can know? Sen. Marco Rubio (R-Fla.) claimed recently that human life begins at conception, and that this is a scientific fact.

There are two stock responses to such a statement, both obscurantist. The first is the tack Philip Bump took in trying to create a gotcha blog post about Rubio's statement. Bump promised to boldly look into the science of human life's origins, and boldly came back saying that there isn't any. After querying a medical definition of pregnancy and sending it to Rubio's office for comment, Bump threw up his hands and retreated from the science altogether:

"Life" is something of a philosophical question, making Rubio's dependence on a scientific argument — which, it hardly bears mentioning, is an argument about abortion — politically tricky. After all, if someone were to argue that life begins at implantation, it's hard to find a moral argument against forms of birth control that prevent that from happening. If that someone were, say, running for president as a conservative Republican, that could be problematic. [Washington Post]

Bump takes the currently unresolved debate about legal personhood and simply transposes it onto the facts of biology after a halfhearted gesture at investigation. His entire argument — "What's human life anyway? Can we really know?" — amounts to a pose of humble sophistication that amounts to saying, "I don't know where babies come from."

The science is pretty straightforward about when a human life begins. You can watch visualizations of it on YouTube. After the fusion of sperm and egg, the resulting zygote has unique human DNA from which we can deduce the identity of its biological parents. It begins the process of cell division, and it has a metabolic action that will not end until it dies, whether that is in a few days because it never implants on the uterine wall, or years later in a gruesome fishing accident, or a century later in a hospital room filled with beloved grandchildren.

In the case of identical twins, the zygote divides and two separate metabolic processes begin using the same genetic code. This is an observed phenomenon. Hand-waving about whether we categorize viruses as "life," for example, doesn't obtrude on these facts, since human zygotes cannot develop into viruses or nonhuman forms of life. Biology doesn't really give us options for when an individual life begins, at least none that we could deny without also denying our ability to know whether any individual members of a species "really exist."

The second response is to nonchalantly acknowledge that human life does begin at conception, but to say that it is a nefarious and misleading distraction, or at least has no bearing on how we should think about legal abortion.

My colleague Ryan Cooper writes that he is "fine with the idea that an abortion represents the end of life, which I distinguish from the idea of a human being." And he continues:

The point is that science has little to do with this argument. Science has enormous cultural legitimacy, so I can see why people want to claim it for their own position, or try to quibble with the definition of life. But when it comes to abortion, science simply doesn't have much to say. [The Week]

But, of course, it's not just the cultural legitimacy of science that anti-abortion activists and writers want to invoke. The very existence of the first argument that "we cannot know" when life begins, à la Bump, testifies to the fact that many people are not at all "fine with the idea that an abortion represents the end of life." Many are, in fact, uncomfortable with the idea of having a category of human life that is not granted a status of "humanity."

When anti-abortion activists say that human life begins at conception, they are not trying to confuse people about whether legal personhood and a viable conceptus are actually the same thing. They are trying to reinforce and build on the common intuition that society's notions about human life should have some correspondence to observable reality, and that legal personhood should have a relationship to when we know a new individual of the species comes into existence. In this respect, anti-abortion advocates see themselves as advocates of a reality-based community, and so they show little patience with arguments that we can generate our own private meanings about when life begins.

And, yes, these activists and pamphleteers do get a kick out of appealing to the authority of science over the willful denials of others. Look at how much fun novelist Walker Percy had doing just that some 33 years ago:

The onset of individual life is not a dogma of the church but a fact of science. How much more convenient if we lived in the 13th century, when no one knew anything about microbiology and arguments about the onset of life were legitimate. Compared to a modern textbook of embryology, Thomas Aquinas sounds like an American Civil Liberties Union member. Nowadays it is not some misguided ecclesiastics who are trying to suppress an embarrassing scientific fact. It is the secular juridical-journalistic establishment. [The New York Times]