Should we engineer genetic changes in human beings? Ought we to use the human organism as a cell or organ bank to provide spare parts? Is it wrong to buy or sell human tissue? Should we experiment on human embryos or children? We are on the brink of a revolution with far-reaching implications. The revolution in molecular biology is expected to give us the ability to divert and control human evolution to an unprecedented extent. It will enable us to manufacture new life forms to order, and to make radical changes to human beings and human nature itself. In Wonderwoman and Superman John Harris argues that the decision before us now is not whether to use this power but how and to what extent. To try to ignore or reject advances in human biotechnology would be futile and might lead to an immense amount of avoidable suffering. There is no safe path, however, and more positive interventions may also lead to considerable harm. What we must do is learn to choose responsibly, and this book is about the ethics of the choices that confront us.