[Moral dignity at the beginning of life. The embryo as a marginal being].

Ethical questions in relation to human embryos in vitro are today raised by reproductive medicine, preimplantation genetic diagnosis and stem cell research. Various discourses--biological, political and medical--describe the embryo from different perspectives. Empirical investigations of the perceptions and concerns of patients in IVF treatments provide important insights. Referring to a variety of discourses and perspectives, the paper develops an ethical analysis of the responsibility for embryos in vitro, with a special emphasis on the relationships involved. In the context of current discussions about the moral status of the embryo, the paper differentiates between four different meanings of "potentiality" of the embryo: (a) external potentiality, (b) the tendency towards a developmental pathway, (c) the transitive determination by a program, (d) preformation. For different reasons, (a), (c) and (d) are rejected. On the basis of potentiality in the sense of (b), the embryo can be described as a developmental being that gives its developmental potential continuously to the next stage ("self-transcendence") and is on the way of becoming a human. This is a reason for defending ethical responsibility for human embryos as the moral recognition of a growing dignity that becomes more intense with increasing proximity to birth.