Professor Jack Mahoney SJ pleads eloquently for allowing “babies to be created with DNA from three people” (“Where’s the harm?”, 7 February), but his arguments are unconvincing. He dismisses as a “long stop or default objection” the position that an embryo is a human being from the moment of conception. That objection is relevant, true, but only to procedures that involve discarding spare embryos – but he speaks also of people who consider a young embryo “living tissue but not get sufficiently formed to constitute an ensouled human person”, a view that is not only contrary to modern Catholic teaching but, in my opinion, philosophically unsustainable.More to the point, he distinguishes between “somatic” and “germ