Science can do many things. Since the scientific revolution, we increasingly get the feeling that science can do anything it sets its mind—or calibrates its microscopes—to do. But, of course, that’s not true. There are things that science simply cannot do. One of those things is settle the abortion debate.
The abortion debate hinges on one’s definition of personhood. Contrary to the rhetoric employed, not a single person on either side of the debate believes in murdering innocent persons.
On the pro-choice side, advocates believe that a woman has a right to make her own decisions about her body. And that phrase is key: her body. They believe that the fetus is an extension of the woman’s body. It’s her egg, and it’s growing and developing, but it’s still a part of her body. At some point, that egg will become a person, but prior to that point, it remains a part of the woman’s body and she can choose to have it removed if she wants to. The moment at which a fetus becomes a person is disputed even within the pro-choice camp, but the idea is the same regardless of the timing of personhood.
On the pro-life side, advocates believe that a fetus is a person. Sure, a woman can do with her body what she wants, but the fetus is not her body. It’s a human being. The person is small and inside of her body, to be sure, but that doesn’t entitle the woman to take a human life.
All of this comes down to when exactly a fetus becomes a person. It seems clear that an egg by itself is not a person. It also seems clear that a solitary sperm is not a person. But as soon as these two meet, the debate begins. Many pro-lifers (myself included) believe that personhood begins with fertilization. Other people believe that personhood begins when the fetus is implanted. Or when the heart begins to beat or the brain waves become detectable. Or during a certain trimester. Or at birth. Or even at some point after birth. There are even those who would deny personhood to full grown adults if they have some type of handicap.
The point is, science can tell us exactly what is going on with the growth of the fetus. It can tell us what is going on when fertilization or implantation happen. It can detect and describe the heartbeat and the brain waves.
But science cannot tell us when that fetus becomes a person. Why? Because that is a matter of definition. It is a philosophical question. It is a religious question. We can and should appeal to science in informing our definition of personhood, but we need to understand that this question will not be answered through the scientific method.
And this means that the abortion debate can only be settled at the level of worldview, personal philosophy, and religious beliefs. Christians appeal to the Bible to show that personhood goes all the way back to the womb—even before that, actually. But without divine revelation to guide them, it seems likely that our society will debate the moment of personhood forever.
This does not make the abortion issue futile. Every just cause is worth fighting for. But it does mean that our efforts must be aimed at worldview. Science is a good thing, and it may be useful in illustrating the humanity of even the smallest persons. But we need to recognize that the battle is for the definition of personhood and focus our energies there.
 We need to be careful about this terminology, however, because none of us is completely entitled to “do with our bodies what we want.” We are forbidden by law from putting certain types of drugs into them, for example. We’re also not allowed to sell them for sex. No matter which side of the debate we are on, we have to be clear that a person’s “right to choose” always has limitations.