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How to Prove Life Begins at Conception

Philosophy, science, and common sense all point to the truth that a distinct human life begins at conception

Trent Horn

I remember during my first years as a pro-life advocate arguing with a college student over the question of when life begins. As a crowd swelled around us, he said, “Look, no one knows when life begins. It’s a religious question that can’t be answered!”

I was determined to prove that life began at conception, but, without any data at my fingertips, I blurted out, “Everyone knows life begins at conception. I’ve read twelve embryology textbooks that say so.”

As people began to disperse, an older pro-life man came up to me and smiled. “Twelve books,” he said. “That was quite a line.”

He had me. At that time, I had read excerpts of maybe one or two books, so perhaps I combined the numbers 1 and 2 and came up with 12. More to the point, I had become flustered in the face of the skeptic who denied that anyone can know when life begins.

He probably took a cue from Roe v. Wade, the U.S. Supreme Court case that decriminalized abortion, which said:

We need not resolve the difficult question of when life begins. 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.

Why is there disagreement over this question? The problem is, the question of when human life begins is actually two distinct questions. It can be a scientific question about the beginning of a human organism, or it can be a philosophical question about when a human organism acquires intrinsic value, a right to life, or becomes a “person.” In this essay I’ll focus on the scientific question and show that there is no doubt that unborn children are young, biological human beings.

Making our case

How can pro-life advocates prove the unborn are biological human beings? It may be tempting to use in utero images, or ultrasounds, of children as our sole evidence of their humanity. While this tactic is useful in some cases, it has the potential to reinforce the idea that our human value comes from what we look like instead of what we are. It’s not a good way to demonstrate the humanity of a four-week-old child who resembles a tadpole.

Pro-life advocates should also avoid making simplistic claims such as “Abortion kills a life” or even “Human life begins at conception.” This leaves them open to a rebuttal such as this one from atheist Carl Sagan:

Despite many claims to the contrary, life does not begin at conception: It is an unbroken chain that stretches back nearly to the origin of the Earth, 4.6 billion years ago. Nor does human life begin at conception: It is an unbroken chain dating back to the origin of our species, hundreds of thousands of years ago (Billions & Billions, 201).

While it is true that living cells or human cells have a long history, the same is not true for individual human beings. Sagan’s criticism is overcome if we drop the assertion “Life begins at conception” and say instead, “A human organism begins to exist at conception” or “The life of an individual human being begins at conception.”

The difference may seem like purely semantical, but it is important to use this vocabulary with pro-choice advocates who may think an embryo is alive in the same sense that sperm and egg are alive. This mistaken set of assumptions may cause the pro-choice advocate to think that an embryo’s life never really began at conception. He might instead think that at conception life in the form of sperm and egg was rearranged and became life in the form of an embryo. This new “rearrangement” would then have the same value as an egg or sperm until it becomes a human being later in pregnancy.

When it comes to defending the claim that an individual human being begins to exist at conception, I don’t recommend generic appeals to authority such as “Science says life begins at conception” or “All scientists agree life begins at conception.” The members of your audience may simply not believe you, or they may think the authorities you are citing are wrong. Instead, I recommend using a simple argument that shows that at conception two body parts (sperm and egg) recombine and form a new living, whole, human organism who is growing and developing into adulthood.

My favorite argument for the humanity of the unborn is based on Steve Wagner’s “10-second pro-life apologist” (Common Ground Without Compromise, 69). Steve was once flustered that he could not defend his pro-life beliefs in an impromptu conversation, so he crafted a 10-second sound bite that goes like this:

  • If it’s growing, isn’t it alive?
  • If it has human parents, isn’t it human?
  • And human beings like you and me are valuable, aren’t we?

Sometimes Steve’s sound bite will do the trick, and the person to whom you are talking will accept that the unborn are biological human beings. Other times you may have to use more evidence to prove that the unborn are (1) alive, (2) human, and (3) whole organisms.

Are the unborn alive?

Clearly, the unborn are alive, because they are receiving nutrients from their mother that cause them to grow via cellular reproduction. I’ve heard some argue that the unborn are not alive because they can’t survive without their mothers or because they can’t survive outside of her body. The problem with these objections is that they prove only that the unborn are alive in a certain place, not that they aren’t alive.

The critic even concedes this when she says that unborn children can’t live on their own or that they can’t live outside the womb. This is just a roundabout way of saying that unborn children live with the assistance of their mothers (just as a newborns can live only with assistance from their mothers or another human). If the fetus is growing, has a heart that is pumping blood through a circulatory system, and is sending electrical signals through a nervous system, how could it not be alive?

Another simple way to show that the unborn are alive is to ask the question, “What does abortion do to the fetus?” Most people will say that abortion kills the fetus, while some stubborn pro-choicers will say abortion removes the fetus from the womb. You can ask these stubborn people what happens to the fetus after it is removed. The critic must admit that the end result of these actions is the death of the fetus. But in order for something to die, wouldn’t it have to be alive at some point?

Of course—but so what if the fetus is alive? Bacteria and oak trees are alive, and we kill them all the time. To answer this objection, we must show that the unborn are not just alive but that they are a special kind of living thing.

Are the unborn human?

Remember that when some people say the unborn are not human, they are usually using the word human in a philosophical sense to mean a valuable human being or a person. Remind them that you want to answer the question, “Are the unborn members of our species?” Only after that question is answered can we debate the philosophical question, “Is every member of our species a person with a right to life?”

When it comes to demonstrating that the unborn are biologically human, or members of our species, there are two kinds of evidence the pro-life advocate can use. First, we can ask what kind of animal the parents of the fetus in question are. If the parents are dogs, then the fetus will be a dog. If the parents are cats, then the fetus will be a cat. If the parents are human, then the fetus will be a human. Second, we (or science) can examine genetic code, or DNA. If the fetus possesses a human genetic code, with approximately forty-six chromosomes, then he is a human being.

Some critics will make this bizarre objection: “It’s not human. It’s a fetus.” When a pro-choice student tried to make this argument in front of a crowd of cheering protesters, I asked in reply, “What is a fetus? Could you define what that word means, or what it refers to?” The protester became uncomfortable and said, “Well, if you’re so smart, why don’t you tell me what the word fetus means?”

“I’d be happy to,” I said. “Fetus is a Latin word that means ‘little one.’ According to most medical dictionaries, among humans, fetus refers to a human being from the eighth week of life until birth. An embryo is a human being from conception until the seventh week of life. The words embryo and fetus are like toddler and teenager—they are stages of development in the life of a human being. So isn’t a fetus by definition human?”

At this point some critics say, “If sperm and egg are alive and human, and fetuses and embryos are also alive and human, then aren’t sperm and egg human beings in the same sense that fetuses and embryos are human beings? Isn’t it an act of homicide to kill sperm or egg cells?”

Sperm, egg, fetus, and toddler are all human in the adjectival sense of the word, since they possess human DNA. Unlike sperms and eggs, however, fetuses and toddlers are also human in the nounal sense of the word. A fetus is a human and a toddler is a human, while an individual sperm cell or egg cell is not a human. This is similar to how we might say apple pie and the U.S. president are both American, but the president is an American, and the apple pie is not. Since sperm cells and egg cells are not individual humans, the act of destroying these cells is not an act of homicide.

This helps answer another common objection: “A blueprint is not a house, and an embryo with human DNA is not a human being.” The problem with this argument is that pro-life advocates don’t say a mere strand of human DNA is a human being (or “a blueprint is a house”). We are saying that an embryo with human DNA is a human being because it is a human organism. A human embryo is more like a complex computer with instructions (i.e., DNA) that allow it to acquire new parts and build itself, and not like a simple blueprint.

Put simply, a human embryo is a human organism and not a mere clump of human tissue like sperm cells or cancer cells. A human being in the embryonic stage of life differs from you and every other born human being only in terms of size, level of development, location, and degree of dependency. Just as we don’t discriminate against born human organisms (aka human beings) that differ in these ways, we should not discriminate against unborn human organisms just because they also differ in these ways.

Are the unborn organisms?

What do we mean when we say the unborn is an organism? According to the Oxford English Dictionary, an organism is a collection of biological parts, or organs, that function together to sustain the existence of a whole being that possesses the qualities of life. I use the following simple test to show something is an organism and not just a clump of cells:

“If I can give this living thing time, nutrition, and a proper environment, and it is able to develop toward becoming a mature member of its species, then it is an organism and not a mere body part.”

Body cells such as skin, sperm, and egg—even given time, nutrition, and any environment— can never develop into an adult human, so they fail the organism test. You and I, however, are organisms, because if we are given time, food, and the proper environment (i.e., not on the moon or at the bottom of the ocean), we will continue to develop into mature members of the human species.

Likewise, an unborn child, when given time, nutrition, and a proper environment (i.e., not outside the uterus) will develop into a mature human being if he does not die prematurely. Embryologist E.L. Potter points out, “Every time a sperm cell and ovum unite, a new being is created which is alive and will continue to live unless its death is brought about by some specific condition” (Pathology of the Fetus and the Infant, 3rd ed., vii).

From the moment they begin to exist at conception, the unborn differ in kind from human tissue or body parts like sperm, egg, or skin cells. Unborn humans are also not like cancerous tumors that can grow and even sprout body parts such as hair or teeth but lack the potential to develop into an adult human. The fact that some embryos and even other born children die before they become adult humans does not negate the fact that they are human beings, because they have the intrinsic capacity to develop into a mature member of the species—even if their development is tragically cut short.

Pro-choice bioethicist Peter Singer agrees. “[T]here is no doubt that from the first moments of its existence an embryo conceived from human sperm and eggs is a human being,” he writes, “and the same is true of the most profoundly and irreparably intellectually disabled human being, even of an anencephalic infant—that is, an infant that, as a result of a defect in the formation of the neural tube, has no brain” (Practical Ethics, 3rd ed., 73).

Just a parasite?

At this point some critics argue that an organism has to exist independently of other organisms. Because an unborn child requires his mother’s body to live, these critics maintain he isn’t independent and so is not an organism. Some people will go so far as to say that the child’s dependence makes him a parasite, and that is why abortion is not wrong.

The description of the unborn as a parasite is inaccurate, as is demonstrated in Thomas L. Johnson’s excellent essay “Why the Embryo or Fetus Is Not a Parasite.” But even if this claim were accurate, it would not help the critic’s case, since parasites are a kind of organism. To say an organism exists independently of another organism simply means it can’t be a literal part of another being, such as an arm or a leg. It has to be able to develop itself apart from any other organism’s DNA. This doesn’t mean, however, that the organism survives without interacting with or depending on any other organism in order to survive. There are hardly any organisms like that.

We normally do have the right to kill parasites, but that is true only because parasites usually belong to species that have no right to live. Since the unborn are human organisms, and thus human beings, calling them “parasites” because of how dependent they are is as offensive as calling mentally handicapped persons “retards” because of how less developed they are.

A student of history will also remember that, during the Holocaust, the Nazis called Jews parasites and used it as a rationale for exterminating them. Does the critic really want to invoke this same kind of rhetoric against another group of human beings?

Call in the experts

Once you have defended the claim that from conception the unborn are biological human beings by using the 10-second pro-life apologist, it is more than appropriate to augment that argument with appeals to relevant authorities. For example, in Planned Parenthood v. Rounds (2008), the Eighth Circuit Court of Appeals found that requiring abortionists to say that the fetus is a “living, separate, whole human being” does not force an abortionist to espouse an unconstitutional religious viewpoint. The Court ruled that this statement was a biological fact that even physicians affiliated with Planned Parenthood accept.

Distinguished scientists and philosophers back up the Court’s opinion. The standard medical text Human Embryology and Teratology states, “Although human life is a continuous process, fertilization is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is formed” (8).

Leading pro-choice philosophers agree that human fetuses are human beings. David Boonin, author of A Defense of Abortion, writes, “Perhaps the most straightforward relation between you and me on the one hand and every human fetus on the other is this: All are living members of the same species, homo sapiens. A human fetus after all is simply a human being at a very early stage in his or her development” (20).

After reviewing several medical and embryology textbooks, I have yet to find a single one that denies that a human embryo or fetus is a human organism. Since, by definition, a human fetus is a stage of development for a human organism, I doubt I ever will find such a claim in a serious textbook.

Case closed

When someone tells you, “No one knows when life begins,” ask him, “How do you know that’s true?” Remind him that you are talking about the beginning of a biological human being’s existence, not when humans acquire personhood or the right to life. Disagreement among laymen does not negate the fact that experts, including those who support legal abortion, agree that the life of an individual human organism, or a human being, begins at conception. Once you’ve established this indisputable fact, you can move the pro-life argument forward by asking, “Shouldn’t all members of our species, or all biological human beings, have the same basic rights, including the right to life?”


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