When does human life begin? Pro-life advocates argue that life begins at conception. They’ll tell you this stance isn’t merely theological or philosophical – it’s just good science. To illustrate this, let’s take a look at some quotes found in actual embryology textbooks:

“A zygote is the beginning of a new human being. Human development begins at fertilization, the process during which a male gamete or sperm…unites with a female gamete or oocyte…to form a single cell called a zygote. This highly specialized, totipotent cell marks the beginning of each of us as a unique individual.” – Keith L. Moore & T.V.N. Persaud

“Although life is a continuous process, fertilization is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is thereby formed…The combination of 23 chromosomes present in each pronucleus results in 46 chromosomes in the zygote. Thus the diploid number is restored and the embryonic genome is formed. The embryo now exists as a genetic unity.” – O’Rahilly, Ronan, and Muller

“Almost all higher animals start their lives from a single cell, the fertilized ovum (zygote)…The time of fertilization represents the starting point in the life history, or ontogeny, of the individual.” – Bruce Patten

So there. That settles it. Fertilization is when life begins. Game over, right?

Not so fast. Maybe we don’t know when life begins…

Well, I don’t have to tell you that the other side of the abortion debate isn’t so quick to concede to the science. Many in the pro-choice camp will say the picture is a whole lot murkier than pro-life advocates make it out to be, and that the matter can’t fully be decided by science.

In a WIRED Magazine article entitled ‘Why Science Can’t Say When a Baby’s Life Begins’, the author cautions us to be more agnostic:

“An embryologist might say gastrulation, which is when an embryo can no longer divide to form identical twins. A neuroscientist might say when one can measure brainwaves. As a doctor, Horvath-Cosper says, “I have come to the conclusion that the pregnant woman gets to decide when it’s a person.”…To doctors and scientists, the question of when life begins isn’t a matter of gathering more evidence.”

There’s a lot I can say here, but I’ll resist the urge to respond for now. We also see this kind of agnosticism again on full display in a Slate piece titled ‘When Does Life Begin? It’s Not So Simple’:

“Many scientists would say they don’t know when life begins. There are a series of landmark moments,” said Arthur Caplan, professor and founding head of the Division of Medical Ethics at New York University Langone Medical Center. “The first is conception, the second is the development of the spine, the third the development of the brain, consciousness, and so on.” That perspective, it turns out, has deep roots. It’s also one that resonates for many pregnant women who experience the embryo’s gradual passage to personhood on a visceral level.”

The author goes on to note that even entire Christian denominations and other religions have been divided on the idea of when life actually begins. Many say that it doesn’t begin at conception. Since there’s no consensus in science, theology or philosophy then we just ought to leave it up to women, right?

What you might not know is this: This reasoning is totally recycled. It’s the same kind of conclusion that the Supreme Court came to originally in Roe v. Wade. Associate Justice Harry Blackmun, speaking for the majority, said the Court was unable to determine when life begins. He wrote: ‘‘When those trained in the respective disciplines of medicine, philosophy, and theology are unable to arrive at any consensus…the judiciary, at this point in the development of man’s knowledge, is not in a position to speculate as to the answer.”

You might be tempted to ask what’s so wrong with this kind of logic.

Skepticism about when life begins doesn’t justify abortion

Well, here’s the thing: This kind of skepticism about when life really begins can’t possibly warrant justifying abortion. Why?

Philosopher Peter Kreeft offers the following quadrilemma:



“When does a person begin? That’s the crucial question.

Well, there’s two possibilities: a.) maybe you know that and b.) maybe you don’t.

And then there are two possibilities. a.) You are right or b.) you are wrong.

So, number one: a fetus is a person, and you know it. You’re right. Number two: the fetus is not a person and you know that. You’re right. Number three: a fetus is a person and you don’t know that. You think it’s not. You’re wrong. Number four: the fetus is not a person and you think it is. You don’t know the truth. You’re wrong.

What is abortion in each of these cases? The only four possible cases, logically.

Murder . Case number one: A fetus is a human person, and you know that it is a human person, and nevertheless you kill it. That’s murder. That’s the legal definition of murder. Knowingly and deliberately imposing violent death upon an innocent human person that you know to be an innocent human person.

Manslaughter . The second possibility. The fetus is, in fact, a person, and you don’t know that. You think it’s not a person. You sincerely believe that “Well, maybe it’s not a person, I don’t know it. I don’t know whether it is or not,” and you kill it. What’s that? Legally, that is manslaughter. Not deliberate murder. It’s like running over an overcoat on a dark night in the middle of a highway, that has the shape of a human being, and it might be an old drunk who’s just lying there, stoned in the road. And it might just be an overcoat. And you don’t swerve, you deliberately run over it. Or, it’s like shooting a movement in the bush that might be a deer, and it might be your fellow hunter. Or, it’s like fumigating a dormitory without being sure that all the students are out, and the fumigation kills them. You might be lucky. You might find that there is no man under the coat, and there is no hunter behind the bush, and there is no student in the dormitory, but you didn’t know that and nevertheless, you shot, you fumigated.

Criminal Negligence . That’s criminal negligence if there’s nobody there, it’s manslaughter if there is somebody there. All three cases—murder, criminal negligence, and manslaughter—are bad.

So only the fourth case justifies abortion.

So, if you can give me some argument that the fourth case is true—not just that a fetus is not a human person, but also you know that it is not a human person, then fine. You’re right. But if you don’t know, if you’re a skeptic, if you say “These pro-lifers are dogmatists, they claim a fetus is a person. Who knows?” Well, that’s all the more reason for not shooting. Exactly because you don’t know.”

This is an airtight argument. The logic here is inescapable. Unless the pro-choicer can say with 100% certainty that the unborn isn’t a human being, they’re guilty of a heinous crime. The only way out is to take the position that the pro-choicer can’t say, and what the justices that decided Roe v. Wade couldn’t say. They couldn’t say for certain that the unborn are human. The Court’s reasoning was hopelessly flawed and morally bankrupt. The same can be said for this type of reasoning continuing today.

Skepticism regarding abortion is at best criminal negligence. It’s manslaughter at worst. If we cannot agree for sure when life begins then that is a reason to not to support abortion, not the other way around. The sad thing is that there are many who think that abortion is willfully killing an innocent human being and don’t seem care these days. Minds this depraved are beyond logic and reason, they need the grace of God.

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