In Better than Human?, noted bioethicist Allen Buchanan grapples with the ethical dilemmas of the medical revolution now upon us. Biomedical enhancements, he writes, can make us smarter, have better memories, be stronger, quicker, have more stamina, live much longer, be more resistant to disease and to the frailties of aging, and enjoy richer emotional lives. They can even improve our character, or at least strengthen our powers of self-control. In...