Abstract

Until recently, the answer to that question was obvious: from fertilization. The discovery that artificial cellular constructs, by nuclear transfer from adult cells and by other techniques, can produce blastocyst-like structures, which under some conditions may develop into embryos upon uterine implantation, with no fertilization, leads us to consider successful uterine implantation as necessary for the qualification of what is an embryo. This implies replacement of essentialist definitions by evolutionary ones. In addition, the concept of potentiality must not be restricted to genome formation but extended to subsequent epigenetic events in embryonic development.

Key-words:

Embryonic stem cells, Embryo research, Status of embryo, Beginning of life, Potentiality of personhood.