Recent advances in techniques and understanding in the fields of genetics, embryology and reproductive biology have opened up new ways to treat a wide range of medical problems. They range from new options for infertility treatment and pre-implantation genetic diagnosis to stem-cell-based therapies for debilitating diseases. Since all these approaches involve the manipulation of human gametes, embryos or embryonic cells, and could also permit more contentious uses, they have stimulated a controversial debate as to what aims are desirable and to what extent experiments on human embryos are...