David Albert Jones is Director of the Anscombe Bioethics Centre, Oxford, and Visiting Professor of Bioethics at St Mary's University College, London, UK. His previous book, "Soul of the Embryo" (Continuum, 2004) was shortlisted for the Michael Ramsey prize.Calum MacKellar is Director of Research with the Scottish Council on Human Bioethics, Edinburgh, UK and Visiting Professor of Bioethics at St Mary's University College, London, UK.