Embryonic Debate
A Reply to William Saletan, liberal bioethics writer, former embryo.


In yesterday’s New York Times Book Review, William Saletan of Slate magazine reviewed our new book Embryo:  A Defense of Human Life.  Saletan is a deservedly respected bioethics journalist. While he is a determined defender of legal abortion and the public funding of embryo-destructive research, he is not unsympathetic to the concerns of those opposed to these practices.  Unsurprisingly, then, his review of our book, though critical, was neither ungracious nor even unyielding on some important points.  Saletan praised the book’s “essential and timely message.”  He conceded that embryos have a certain moral standing—one that is, presumably, not enjoyed by mere gametes, tissues, or organs.  “We should never create and destroy embryos lightly. We owe them our respect.”  Yet the respect to which embryos are entitled, Saletan evidently believes, is not inconsistent with what he himself describes (in considering cloning) as “the mass production, exploitation, and destruction of human embryos.”

In attempting to resist our conclusion that human embryos ought not to be exploited and killed, while at the same time acknowledging their moral standing and the special respect they are owed, Saletan gets himself into a jam.  To meet our argument that a human embryo is, as a matter of scientific fact, a developing human being—i.e., a living member of the species Homo sapiens in the earliest stages of development—and thus, as a matter of basic justice, a possessor of inherent dignity and a right to life, Saletan is driven to deny that human embryos are whole entities, as opposed to mere parts (such as gametes, tissues, or organs).  He denies that embryos are determinate individuals, and he seems to doubt that they are organisms at all.  But if these denials and doubts are warranted, then there is no rational basis for believing that human embryos “deserve our respect” or that “we should never create or destroy them lightly.”  Saletan is trying to find a plot of solid ground lying between the views of radical liberal bioethicists, on the one side, and defenders of the pro-life view, on the other.  The failure of his effort shows that the middle ground is nothing but quicksand. 

Saletan’s denial that human embryos are human beings in the embryonic stage of development cannot be sustained in light of the scientific facts.  Modern embryology and human developmental biology establish beyond any doubt that human embryos are wholes and not mere parts, that they are indeed determinate individuals; and that they are organisms that endure throughout the developmental process, that is, both during gestation and after birth. 

Consider any adult human being—William Saletan, for example.  He is the same whole living individual human organism—i.e., the same human being—that was at an earlier stage of his life an adolescent.  And the adolescent Will was the same whole living individual human organism that was at earlier developmental stages a child, an infant, a fetus, and an embryo. By contrast, he was never an ovum or a sperm cell.  The gametes whose felicitous union brought the embryonic Will Saletan into existence were parts of other organisms, his mother and father.  But Will was once an embryo, just as he was once a fetus, an infant, a child, and an adolescent.  From the embryonic stage forward, Will was a complete (though in the beginning developmentally immature) and distinct (both genetically and functionally) organism.  He developed by an internally directed and gapless process from the embryonic into and through the infant, child, and adolescent stages and ultimately into adulthood with his organismic determinateness, distinctness, and unity intact.

Will, meet Will 
The argument against our view being advanced by the adult Will Saletan is confounded by the fact that Will Saletan, like the rest of us, really was once an embryo.  In telling the story of Will’s life, it would be a howler of a scientific mistake to say that once upon a time there was an embryo that was something distinct from the living human organism that is now Will Saletan, but that got transformed from whatever it was into the organism that is Will Saletan at some point after the embryo came into existence.  The true story is that the organism that is Will Saletan is the same organism that, at an earlier stage of Will’s development, was that embryo

Let’s now examine the specific claims about embryogenesis and early intrauterine human development on the basis of which Saletan tries to make his case against our position.  He quotes us saying that “nothing extrinsic to the developing organism itself acts on it to produce a new character or direction of growth.”  But despite having quoted us on this point in full, Saletan mistakenly argues against the quite different claim that nothing acts on the embryo at all.  We do not make this claim and it is unnecessary to make in order to establish that human embryos are, as a matter of biological fact, new and distinct individuals of the human species.  We did not claim comprehensively that nothing acts on the embryo.  Such a claim would be false of the human embryo and perhaps every other developing organism, whether that organism is in utero, if viviparous, or in an egg, if oviparous.  Developing organisms (including humans during gestation and even after birth) are dependent in various ways and often depend upon environmental cues and prompts for certain aspects of their development.  In some cases, development will even stall while the organism waits for environmental signals indicating, say, receptivity for implantation, in the case of embryos of certain species. 

In the early development of a human being, the embryo requires maternal signaling of receptivity for successful implantation.  Yet, as every human embryology text affirms, even during the process of implantation the embryo is acting as a distinct biological unit—an organism.  The embryo is not a maternal body part.  No text of modern embryology even remotely suggests such a thing.  As Saletan notices, the embryo acts on the mother, just as she acts on him or her.  He quotes an embryology text saying that “the early embryo and the female reproductive tract influence one another.”  Indeed, they do.  (For example, the embryonic human secretes human chorionic gonadotropin, which helps to maintain the maternal secretion of progesterone and estrogen without which menstruation would begin and the embryo would be expelled.)  But the interactions of mother and developing child in no way warrant the conclusion Saletan seems to want to draw, namely, that the embryo is not a whole, distinct, living organism. 

Consider the Science
Our claim was not that nothing acts on the embryo in the developmental process.  It was that nothing acts on the embryo in such a way as to “produce a new character or new direction of growth.”  This is a straightforward fact fully established by embryological science.  Nothing in the developmental process (certainly no action of the mother) transforms the developing organism from one kind of entity (say a nonorganismic entity or a nonhuman organism) into another kind of entity (a human).  Human development is the development of an entity that comes into existence as, and remains until death, a complete, self-integrating, determinate human organism—a human being.  Indeed, we can see this in the fact that the effect had by the mother on her developing child is species specific:  maternal signaling, the provision of nutrition and an environment hospitable to the child’s life and development,  and other maternal factors help to enable the embryo and fetus to continue along the distinctive developmental pathway determined by the embryo itself.  When zebra embryos are experimentally transferred to horse mares, such trans-species pregnancies can proceed successfully to term, but invariably result in the birth of baby zebras, not baby horses or zebra-horse hybrids.  The maternal environment supports and influences the development of the embryo, but does not control development. Similarly, no maternal or other extrinsic action changes the human embryo from a human being or into a human being; they merely enable it to continue to grow and develop as a human being.   

Similar points could be made about another feature of embryonic development to which Saletan alludes in trying to resist our defense of the embryo, i.e., the influence of maternal RNA on early embryonic development.  The RNA is “maternal” only in the sense that it is contributed by the oocyte.  But as human embryologist Maureen Condic explains, “once an embryo has come into existence, the maternally-derived RNA, like the embryo’s genome, belong to the embryo itself.  They are not components of the mother, somehow acting at a distance, but components of the embryo acting to further its own development.”  They form aspects of the complete developmental program of the embryo and are neither extrinsic, nor distinct agents.  (Nor do they cause the embryo of some early stage to become a numerically different being.)  These facts discredit Saletan’s claim—central to his case against our position—that “maternal factors don’t just facilitate the embryo’s program; they direct it.”  The truth is that the embryo’s development is internally directed.  The embryo directs not only its own integral organic functioning, but also its development in the direction of maturity as a member of the human species.     

If a human embryo were something other than a human being in the embryonic stage of development—an embryonic human being—what could it be?  Saletan’s suggestion seems to be, not simply that the embryo is less than a human being, but that the mother and embryo taken together form the relevant biological unit.  Writing of the mother’s relation to the developing embryo, he says that “[h]er body sustains it, guides it and affects its direction of growth.  Mother and child are a system.”  Later, Saletan casts an even wider net in search of the relevant unit:  The biological program for humanity “doesn’t run on one body.  It runs on the network of humanity.  In fact, it runs on the entire Internet of evolving species.”