Abstract

A basic component of moral objections to embryonic stem cell research is the claim that human embryos have the same moral status as typical adult human beings. There is no reason to accept this claim, however, unless adult humans once existed as embryos—that is, unless the developmental history of adult humans contains embryos to which the adults are numerically identical. The purpose of this paper is to argue that there are no such identities, and hence that no adult human being ever existed as an embryo.