LEON Kass is a man with a mission. Life, Liberty and the Defense of Dignity, † a good portion of which has already appeared in print in Commentary, First Things, The Hastings Center Report, The New Republic, and this journal, draws together Kass’s elegant and complex arguments against the biotechnological drive now well underway.  Kass, chair of the President’s Council on Bioethics, takes pains to assure readers at the outset that he is no Luddite; that he recognizes and appreciates the enormous contributions biomedical technology has made to human well-being; and that he is a friend of modern liberal democracy.  In large part because the accomplishments of biotechnology have been so stunning, Americans are culturally ill-prepared to deal in any systematic way with threats emanating from this direction. For Kass, nothing less than our humanity is at stake in this debate, and the outcome is by no means guaranteed.