The Metaphysical Status of the Embryo: Some Arguments Revisited

abstract This paper re-examines some well-known and commonly accepted arguments for the non-individuality of the embryo, due mainly to the work of John Harris. The first concerns the alleged non-differentiation of the embryoblast from the trophoblast. The second concerns monozygotic twinning and the relevance of the primitive streak. The third concerns the totipotency of the cells of the early embryo. I argue that on a proper analysis of both the empirical facts of embryological development, and the metaphysical importance or otherwise of those facts, all three arguments are found wanting. None of them establishes that the embryo is not an individual human being from the moment of conception.