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In an early draft of its next strategic plan, the Department of Health and Human Services has described its mission as “serving and protecting Americans at every stage of life, beginning at conception” [emphasis added]. In an op-ed in the Los Angeles Times, Dr. Richard Paulson—a professor of obstetrics and gynecology and an infertility specialist—vehemently objects to HHS’s affirmation that life begins at conception. Paulson claims that this affirmation is based on religion rather than science, and that HHS should remove it from the report, because the agency’s endorsement of a religious view of human life violates the constitutional separation of church and state.

We heartily agree with Paulson that the HHS should define human life on the basis of “science and data, not faith-based belief.” But on the question of when the life of a new member of the human species comes to be, the scientific facts squarely support the position of HHS, not of Dr. Paulson. How he can be unaware of the pertinent facts is befuddling.

The standard science texts as well as scholarly articles in the fields of embryology, developmental biology, and microbiology assert the very position that Paulson says is merely faith-based and unscientific.

The Science of Embryology

The following are typical examples—only three of the many, many we could cite. These are from standard texts by embryologists, developmental biologists, and microbiologists:

“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. “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 Research. “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, 3rd edition.

Many other examples could be cited, some of which may be found here.

These authorities all agree because the underlying science is clear. At fertilization—or, more precisely, when the sperm (a male sex cell) fuses with the oocyte (a female sex cell, more commonly referred to as an egg)—each of them ceases to be, and a new entity, one that is both genetically and functionally distinct from either parent, 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), which then dissolves during implantation, allowing for continued growth in the direction of maturity as a member of the species. Even prior to implantation, however, these cells and membrane function as parts of a whole that regularly and predictably develops into the more mature stages of a complex human body.

How do we know that the result of sperm-oocyte fusion is a new entity, rather than a continuation of the oocyte? We know that a new entity exists because, once the sperm penetrates the oocyte, a completely new trajectory of biological development commences. The biological activity of an oocyte is directed toward successful fertilization; the biological activity of sperm is directed toward penetration of an oocyte. The biological activity of the new entity that results when sperm and oocyte fuse, however, is directed toward nothing less than the development of a mature human organism, distinct from either parent. Further, this new entity’s activities are directed not by instructions from the mother’s body, as some people wrongly suppose, but by its own unique set of instructions, especially the blueprint for development contained in its unique genetic material. The mother’s body recognizes the zygote and then the embryo as an entity distinct from itself. In fact, the embryo must send out chemical signals to prevent the mother’s immune system from attacking it. The embryo also emits chemical signals that induce changes in the lining of the mother’s uterus to enable successful implantation.

If this embryo is provided a suitable environment, nutrition, and protection from deliberate attack, serious injury, or disease, it will develop to the mature stage of a human organism. Thus, from the zygote stage onward this distinct, new organism has all of the internal resources—in its genetic and epigenetic structure—needed to develop itself (or, rather, himself or herself, since in the human sex is determined from the very beginning) to the mature stage of a human organism. At no point after fertilization—implantation, gastrulation, birth, puberty, etc.—does a fundamental change in biological trajectory occur. These subsequent stages of development are simply the unfolding of the zygote’s inherent dynamism toward human organismal maturity. This shows that the zygote already is a human organism—a member of the species Homo sapiens—albeit at an early stage of his or her development.

Paulson’s Arguments

But perhaps Dr. Paulson objects to HHS’s claim that life begins at conception not because it contradicts the overwhelming scientific consensus, but because he has decisive arguments against that view? We can’t rule that out a priori, so let’s examine his arguments.

First, Paulson claims that no new life is formed at fertilization because the egg and the sperm were already alive: “The human egg is a single living cell and it becomes a one-cell embryo if it successfully combines with a live sperm. No new life is formed — the egg and the sperm were already alive — and fertilization is not instantaneous.” This argument, however, rests on utter confusion.

No one after the work of Louis Pasteur has maintained that life comes from anything other than life. Of course there was life before fertilization (the egg and the sperm). There were living entities—living cells—from which the new living being came to be. But with fertilization there is a new life—that is, there is a new organism, a member of the same species as the parents and no mere part of either of them (as the male or female sex cells were)—an entity that was not there before.

If Paulson’s argument were sound, it would show that no new cells ever come to be, even in the asexual reproduction of cells—for example, within our bodies in cellular growth or repair. In such cases, the parent cell was alive before the reproduction, but of course the two daughter cells really do come to be. Thus, the continuum of life—which Paulson mentions again later in his piece—provides no evidence against the standard scientific view that a new human life comes to be at conception (fertilization).

Second, Paulson suggests that, because fertilization is a process, it can’t be the point at which a new human being comes to be. He writes: “fertilization is not instantaneous. Nearly 48 hours pass from the time sperm first bind to the outside of the zona pellucida, the human eggshell, until the first cell division of the fertilized egg.” But this argument too is stunningly weak. A radical change—in this case the coming to be of a new organism, marked by a radical change in the trajectory of the entity’s biological activity—can be caused by a coordinated series of smaller changes. Many smaller changes—such as the movement of sperm through the uterine tube and then through the outer protective structures of the oocyte—precede the radical change that occurs when one sperm cell penetrates the oocyte and its membrane fuses with the oocyte’s membrane to form a new, genetically distinct, single dynamic structure. As all the works of modern human embryology and developmental biology attest, this radical change marks the coming to be of a new human individual. A series of very small changes—a continuum—is no evidence at all against a discontinuity at the end of that series.

Note also that if Paulson’s argument were sound it would refute his own position as well. A human life can’t begin at conception, he says, because conception is an extended process. So, when does it occur? His answer: later during gestation, possibly with implantation. But of course, implantation too occurs by several small steps. The only point at which there is truly a radical change in biological trajectory—and so the only logical point to locate the generation of the new organism—is fertilization, with the ceasing to be of the male and female sex cells and the simultaneous coming to be of the self-directing new organism.

Third, Paulson claims that prior to implantation the human embryo is merely “a collection of stem cells, each of which has the capacity to grow into any part of the placenta, as well as fetal tissues and organs, but it is not itself a new human life.” But this ignores the internally coordinated collaboration of these cells. The embryo is of course composed of a multitude of cells (though not, it should be pointed out to Paulson, all of them stem cells). And the cells in the part of the embryo called the inner cell mass, when extracted from the human embryo, do qualify as pluripotent cells—that is, once extracted, they can be coaxed to become any type of human cell—but none of this shows that the embryo is a mere mass of undifferentiated cells rather than what it obviously is: an internally integrated organism. Again, all the scientific works acknowledge this fact.

Indeed, cell differentiation begins with the very first cell division. Unless something (such as twinning, discussed below) interferes with their trajectory, one of these two cells will develop into the future body, multiplying itself to form a cluster of cells at one end of the embryo called the inner cell mass. The other will develop into the placenta and other supporting structures, multiplying itself to form a ring of cells that lines the inside of the zona pellucida, leaving a large cavity in the middle of the embryo that is called the blastocoele. Thus, far from being an undifferentiated and unorganized mass, the embryo’s cells communicate and function together as parts of a complex whole in a regular and predictable manner, each new step preparing for the next along a developmental trajectory that, if all goes well, eventually by a continuous and gapless process results in a sixteen-year-old’s asking for the car keys.

Fourth, Paulson suggests that the possibility that an early embryo may give rise to twins (monozygotic) shows that they are not yet individuals: “It is also potentially more than one individual, since identical twins are the result of a single implantation.” However, from the fact that A can split into B and C, it simply does not follow, nor does the fact at all suggest, that A was not an individual before the division. Conceivably, A might cease to be and give rise to B and C, or A might be identical with B or with C. When a flatworm is sliced, the result is two living flatworms. It is obvious that a new individual is generated by the division of parts from a single whole. The fact that the division of a flatworm produces two flatworms in no way shows that prior to that division there was not actually a single flatworm. The evidence indicates that this same type of event occurs with most monozygotic twinning in human beings. That is, in most monozygotic twinning a single embryonic human being exists until the splitting of some cells from this first embryo, and this division generates a second embryo. Thus, monozygotic twinning casts no doubt at all on the fact that the human embryo is a distinct, whole, albeit immature, human organism from conception (fertilization) on.

In short, Dr. Paulson accuses the HHS of presenting a faith-based affirmation as if it were a scientific position. But it turns out that his denial of the claim that life begins at conception contradicts the standard scientific position, and his arguments against that claim are fallacious (sometimes egregiously so) and inaccurate. Ironically, it is Dr. Paulson, not the HHS, who seems to be basing his views about the beginning of human life on something other than scientific facts.