This paper re-examines the question of whether quirks of early human foetal development tell against the view (conceptionism) that we are human beings at conception. A zygote is capable of splitting to give rise to identical twins. Since the zygote cannot be identical with either human being it will become, it cannot already be a human being. Parallel concerns can be raised about chimeras in which two embryos fuse. I argue first that there are just two ways of dealing with (...) cases of fission and fusion and both seem to be available to the conceptionist. One is the Replacement View according to which objects cease to exist when they fission or fuse. The other is the Multiple Occupancy View – both twins may be present already in the zygote and both persist in a chimera. So, is the conceptionist position tenable after all? I argue that it is not. A zygote gives rise not only to a human being but also to a placenta – it cannot already be both a human being and a placenta. Neither approach to fission and fusion can help the conceptionist with this problem. But worse is in store. Both fission and fusion can occur before and after the development of the inner cell mass of the blastocyst – the entity which becomes the embryo proper. The idea that we become human beings with the arrival of the inner cell mass leads to bizarre results however we choose to accommodate fission and fusion. (shrink)

When Did I Begin? investigates the theoretical, moral, and biological issues surrounding the debate over the beginning of human life. With the continuing controversy over the use of in vitro fertilization techniques and experimentation with human embryos, these issues have been forced into the arena of public debate. Following a detailed analysis of the history of the question, Reverend Ford argues that a human individual could not begin before definitive individuation occurs with the appearance of the primitive streak about two (...) weeks after fertilization. This, he argues, is when it becomes finally known whether one or more human individuals are to form from a single egg. Thus, he questions the idea that the fertilized egg itself could be regarded as the beginning of the development of the human individual. The author also differs sharply, however, from those who would delay the beginning of the human person until the brain is formed, or until birth or the onset of conscious states. (shrink)