This chapter may be regarded as an aberration as we move from the world of the dead into the world of the living, by turning our attention to the human embryo. This is no longer the world of cadavers; it is the twilight zone between the world of non-existence and that of the hardly alive, between uncoordinated tissues and the ongoing life of a coherent organism. Just as we have sought to determine the ethical significance of cadavers, we must now consider the ethical significance of the earliest stages of human life. Where should the human embryo sit within a continuum of values, which extends from the limited value of tissues and cells to the full moral status accorded to human persons?