In the next fifty years, life spans will extend well beyond a century. Our senses and cognition will be enhanced. We will have greater control over our emotions and memory. Our bodies and brains will be surrounded by and merged with computer power. The limits of the human body will be transcended as technologies such as artificial intelligence, nanotechnology, and genetic engineering converge and accelerate. With them, we will redesign ourselves and our children into varieties of posthumanity . This prospect is understandably terrifying to many. A loose coalition of groups-including religious conservatives, disability rights and environmental activists-has emerged to oppose the use of genetics to enhance human beings. And with the appointment of conservative philosopher Leon Kass, an opponent of in-vitro fertilization, stem cell research and life extension, to head the President"s Council on Bioethics, and with the recent high-profile writings by authors like Francis...