“Biological entities, in other words, are defined by their characteristic behavior; and that is enough to show that what is generated at conception is a new human being. But by applying the same principle to a more detailed biological picture, we can answer the question to which Caplan shifted: Which event surrounding the meeting of sperm and egg constitutes their transformation into a zygote?”

Senator Marco Rubio is right. The life of a human being begins at conception—not at implantation, “viability,” or birth. This is a scientific fact.

It is not, as CNN journalist Chris Cuomo ignorantly insisted in a televised confrontation with Rubio, a claim of “faith” with no scientific basis. To our surprise, however, the distinguished bioethicist Arthur Caplan has intervened to try to rescue Mr. Cuomo in a fight he is losing and losing badly. According to Professor Caplan, Senator Rubio has the science wrong. But he doesn’t. And Professor Caplan fails to show that he does.

Red Herrings

Caplan first appeals to a resolution issued by the National Academy of Sciences in 1981, in response to a congressional bill asserting “that actual human life exists from conception.”

It would have been clearer to say that what begins at conception is an actual human life—the life of a human individual, a human being. The bill’s vaguer wording allowed the NAS to respond with a blatant dodge: it simply noted that “human life” (as opposed to a human life, the life of a new human individual) is passed on continually across generations. That is true—but irrelevant to the issue at hand. So is the NAS resolution’s next point: that when the embryo becomes “a person” is a philosophical (or theological) question on which science is silent.

That is also true. Science reveals empirical facts. It cannot tell us who, if anyone, is a “person,” morally speaking—which beings, if any, have fundamental dignity and basic moral rights. There are correct answers to these questions—they are not merely subjective issues—but they are not answered by application of scientific methods of inquiry. We cannot determine whether there even is such a thing as human rights, or whether slavery, or Hitler’s genocide against Jews, was morally wrong, by conducting laboratory experiments or constructing mathematical models.

What science can and does reveal is whether a human zygote, embryo, or fetus is a newly conceived human being. This was the question on which Senator Rubio appealed to science. And, contrary to Professor Caplan’s complaint, Rubio got it right. Science shows that the human zygote, embryo, and fetus, like the infant or adolescent, is indeed a human being—a living individual of the human species. And—despite its red herrings and irrelevancies—the Academy did not deny this truth. The 1981 resolution provides no support at all for Professor Caplan’s charge against Rubio.

The Scientific Facts

Readers may wonder why Professor Caplan reached back to a resolution passed by a learned society some thirty-four years ago in seeking authority to support his case against Senator Rubio. Professor Caplan remarks: “Since that time [1981], scientists and physicians have remained more or less mum on the issue of when life begins.” But that is simply incorrect. Before and after 1981, there have been countless scientific monographs and scholarly articles—in embryology, developmental biology, and genetics—explicitly affirming that a human being at the earliest stage of development comes to be at fertilization. Here are three of many, many examples:

“Human life begins at fertilization, the process during which a male gamete or sperm unites with a female gamete or oocyte (ovum) to form a single cell called a zygote. This highly specialized, totipotent cell marked the beginning of each of us as a unique individual.” “A zygote is the beginning of a new human being (i.e., an embryo).” Keith L. Moore, The Developing Human: Clinically Oriented Embryology, 7th edition. Philadelphia, PA: Saunders, 2003. pp. 16, 2.

“Fertilization is the process by which male and female haploid gametes (sperm and egg) unite to produce a genetically distinct individual.” Signorelli et al., Kinases, phosphatases and proteases during sperm capacitation, CELL TISSUE RES. 349(3):765 (Mar. 20, 2012)

“Although life is a continuous process, fertilization (which, incidentally, is not a ‘moment’) is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is formed when the chromosomes of the male and female pronuclei blend in the oocyte” (emphasis added; Ronan O’Rahilly and Fabiola Mueller, Human Embryology and Teratology, 3^rd edition. New York: John Wiley & Sons, 2000, p. 8). (Many other examples could be cited, some of which may be found here. )

That is the authority of science. On request, we can cite dozens more examples. The authorities all agree because the underlying science is clear. At fertilization a sperm (a male sex cell) unites with an oocyte (a female sex cell), each of them ceases to be, and a new entity is generated. This new entity, initially a single totipotent cell, then divides into two cells, then (asynchronously) three, then four, eight and so on, enclosed all the while by a membrane inherited from the oocyte (the zona pellucida). Together, these cells and membrane function as parts of a whole that regularly and predictably develops itself to the more mature stages of a complex human body.

From the zygote stage onward this new organism is distinct, for it grows in its own direction; it is human—obviously, given the genetic structure found in the nuclei of its cells; and it is a whole human organism—as opposed to what is functionally a part of a larger whole, such as a cell, tissue, or organ—since this organism has all of the internal resources and active disposition needed to develop itself (himself or herself) to the mature stage of a human organism. Given its genetic constitution and epigenetic structure, all this organism needs to develop to the mature stage is what human beings at any stage need, namely, a suitable environment, nutrition, and the absence of injury or disease. So it is a whole human organism—a new human individual—at the earliest stage of his or her development.

This is why it is correct to say that the developing human embryo is not “a potential human being” (whatever that might mean) but a human being with potential—the potential to develop himself or herself (sex is established from the beginning in the human) through the fetal, infant, child, and adolescent stages and into adulthood with his or her identity intact.

So the man known to the world as Arthur Caplan is the same human being—the same living individual of the human species—who was once a Columbia graduate student, and before that a gifted Brandeis undergraduate, a rambunctious teenager, a precocious toddler, a newborn infant, a seven-month old fetus, a four-week old embryo, and a newly conceived human being. He was never a sperm cell or an oocyte; those were (genetically and functionally) parts of his parents. But he was once a zygote—a single-celled human individual, distinct from the gametes whose union brought him into being.

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