1. Phoebe R. Berman Bioethics Institute, The Johns Hopkins University, Baltimore, MD 21205, USA.
2. Stem Cell Research Center, University of California, Irvine, CA 92697, USA.
3. Institute of Medicine, Law, and Bioethics, University of Manchester, Manchester M13 9PL, UK.
4. Division of Developmental Genetics, Medical Research Council (MRC) National Institute for Medical Research, London NW7 1AA, UK.
5. Oxford Uehiro Centre for Practical Ethics, University of Oxford, Oxford OX1 1P, UK.