On a free vote, the House of Common has given its overwhelming support for the use of new medical techniques to prevent certain genetic disorders. These techniques involve the transfer of healthy DNA from a third party – hence the misleading phrase “three-parent babies” – to replace damaged DNA in a human egg or embryo. They raise serious ethical issues. If the House of Lords also approves the technique, it will be used to help women have healthy babies whose offspring might otherwise suffer greatly and die in infancy. On any utilitarian calculus, that is progress. How could anyone with any compassion oppose it?Yet objections have been raised, even by those whose compassion cannot be questioned. They ask if the scientists are sure the technique is safe, and whether