The key question in the debate over stem cell research that involves the destruction of human embryos is: When does the life of a human being begin? To answer this question is to decide whether human embryos are, in fact, human beings and, as such, possessors of inherent human dignity.
Where do we go to find the answer? Not, in my opinion, to the Bible, Talmud or other religious writings, even if we regard these texts as sources of moral wisdom and even divine revelation. Nor should we be satisfied to consult our "moral intuitions."
Rather, the answer is to be found in the works of modern human embryology and developmental biology. In these texts, we find little or nothing in the way of scientific uncertainty: "…human development begins at fertilization…" write embryologists Keith Moore and T.V. N. Persaud in The Developing Human (7th edition, 2003), the most widely used textbook on human embryology.
Robert P. George is a member of the President's Council on Bioethics. He is also a professor of jurisprudence and director of the James Madison Program in American Ideals and Institutions at Princeton University.
A human embryo is a whole living member of the species Homo sapiens in the earliest stage of development. Unless severely damaged or deprived of nutrition or a suitable environment, the embryonic human will develop himself or herself by an internally directed process to the next more mature developmental stage, i.e., the fetal stage.
The embryonic, fetal, infant, child and adolescent stages are stages of development of a determinate and enduring entity -- a human being -- who comes into existence as a zygote and develops by a gradual and gapless process into adulthood many years later.
Whether produced by fertilization or cloning, the human embryo is a complete and distinct human organism possessing all of the genetic material needed to inform and organize its growth, as well as an active disposition to develop itself using that information. The direction of its growth is not extrinsically determined, but is in accord with the genetic information within it.
The human embryo is not something different in kind from a human being, nor is it merely a "potential human being," whatever that might mean. Rather the human embryo is a human being in the embryonic stage.
The adult that is you is the same human being who, at an earlier stage of your life, was an adolescent, and before that a child, an infant, a fetus and an embryo. Even in the embryonic stage, you were a whole, living member of the species Homo sapiens. You were then, as you are now, a distinct and complete -- though, of course, immature -- human organism.
Unlike the embryo, the sperm and egg whose union brings a human being into existence are not complete organisms. They are both functionally and genetically identifiable as parts of the male or female parents. Each has only half the genetic material needed to guide the development of a new human being toward maturity. They are destined either to combine to generate a new and distinct organism or simply die.
Even when fertilization occurs, the gametes do not survive: Their genetic material enters into the composition of a new organism. (A somatic cell that might be used to produce a human being by cloning is analogous not to a human embryo, but to gametes.) The difference between human gametes and a human being is a difference in kind, not a difference in stage of development. The difference between an embryonic human being (or a human fetus or infant) and an adult is merely a difference in stage of development.
Some today deny the moral premise of my position, namely, that human beings possess inherent dignity and a right to life simply by virtue of their humanity. They claim that some, but not all, human beings have dignity and rights. To have such rights, they say, human beings must possess some quality or set of qualities (sentience, self-consciousness, the immediately exercisable capacity for human mental functions, etc.) that other human beings do not possess or do not yet possess, or no longer possess.
I reject the idea that human beings at certain stages of development (embryos, fetuses, infants) or in certain conditions (the severely handicapped or mentally retarded, those suffering dementia) are not "persons" who possess dignity and a right to life. And no person may legitimately be destroyed in biomedical research or for other reasons.