Human Embryos, Human Beings: A Scientific and Philosophical Approach by Samuel B. Condic and Maureen L. Condic (review)

Samuel Condic and Maureen Condic begin their excellent book, Human Embryos, Human Beings: A Scientific and Philosophical Approach, by noting that a careful analysis of the facts regarding when a new human being (by contrast with mere human cells) comes into existence is crucial for the resolution of many contemporary public debates. Combining the authors' respective areas of expertise in philosophy and biology, the book presents a powerful case that human embryos are human beings from the very beginning of their existence—that is, at sperm–egg fusion.

After providing a broadly accessible explanation and defense of basic Aristotelian metaphysical principles in chapter 1, in the subsequent chapters the authors engage with several lines of argument against the claim that an embryo is a human being (rather than a mere clump of human cells). Chapter 2, for instance, begins by addressing Joseph Donceel's influential argument that the embryo cannot be a human being, because the embryo is in the process of developing distinctively human traits, and "nothing that is only developing distinctly human traits can be human now." The authors offer a persuasive criticism of this argument and present an alternative account, based on Aristotelian-Thomistic hylomorphism, in defense of the claim that "since the early embryo can support both life and growth, the possibility of immediate hominization cannot be dismissed."

In chapter 3, Condic and Condic discuss the arguments of those skeptical that embryos are human beings due to the totipotency (or rather plenipotency) of embryos' cells and the corresponding capacity for twinning that some early embryos possess. The authors make an interesting distinction between totipotent and plenipotent cells. A zygote counts as totipotent "because it has the ability to form a complete body." By contrast, plenipotent cells are "capable of forming all the tissue types found in the embryo . . . but not the complete body as an organized, functional whole." This distinction is important because, unless some external agency induces twinning, the early embryo's cells are not totipotent but plenipotent, which means that "the embryo cannot be thought of simply as a collection of cells, each with the active potential to become human." Further, they clarify that despite an early embryo's capacity for twinning, it is incorrect to say that one embryo is in fact multiple individuals, as some who are skeptical of the embryo's humanity claim. Rather, the authors clarify that the potential of an embryo to become two embryos is remote and requires the intervention of a mediating act that disaggregates, just as individual flatworms require the intervention of a mediating act (that is, a knife cutting them in half) to become two flatworms. In both cases, the entity prior to the mediating act was only a single individual.

In chapter 4 the authors try to determine, on the basis of biological facts, at what point the power for self-directed growth toward human maturity (what the authors call the augmentative power, following Aquinas) is actually present. At sperm–egg fusion? Or after syngamy (the intertwining of sperm and egg DNA)? The authors provide ample evidence that, beginning at sperm–egg fusion and within minutes of that fusion, a number of important biological changes occur that involve "active collaboration between maternally and paternally derived elements," and that are directed toward the maturation of the embryo as a whole. They also argue convincingly that what matters is not the extent to which the embryo's activities are directed by the genome, but rather that the embryo manifest self-directed development toward maturity.

Chapters 5 and 6 consider the arguments of those who think that we have insufficient evidence to determine whether or not an embryo is a human being, and therefore must make the determination by pure "fiat." Chapter 5 discusses developmental systems theory, acknowledging its merits in counterbalancing an overly "gene-centric" view of organisms, but noting...