But are human embryos human beings?
Indeed they are, and contemporary human embryology and developmental biology leave no significant room for doubt about it. The adult human being reading these words was, at an earlier stage of his or her life, an adolescent, and before that an infant. At still earlier stages he or she was a fetus and before that an embryo. In the infant, fetal, and embryonic stages, each of us was then what we are now, namely, a whole living member of the species Homo sapiens. Each of us developed by a gradual, unified, and self-directed process from the embryonic into and through the fetal, infant, child, and adolescent stages of human development, and into adulthood, with his or her determinateness, unity, and identity fully intact. Although none of us was ever a sperm cell or an ovum—the sperm and ovum from whose union we emerged were genetically and functionally parts of other human beings—each of us was once an embryo, just as we were once infants, children, and adolescents. In referring to “the embryo,” then, we are referring not to something distinct from the human being that each of us is, but rather to a certain stage in the development of each human being—like saying “the teenager” or “the five-year old.”