An argument that achieving millennial life spans or monumental intellects will destroy values that give meaning to human lives.

"Arguments against radical enhancement have too often in the past been characterized by irrationalism and mysticism. Nicholas Agar presents the first cogent case for the rationality of opposing radical enhancement. Moving easily between science and philosophy, he argues for a species-relative conception of valuable experiences, according to which we have a strong reason to remain human. This central claim is bolstered by a host of other arguments, which will ensure that Humanity's End will become a central reference point for debates over the desirability of radical enhancement." Neil Levy, Oxford Centre for Neuroethics "Nicholas Agar has written an excellent introduction to the moral challenges of our transition to a posthuman future, engagingly told by contrasting the work of four very different transhumanists. Humanity's End joins Agar's Liberal Eugenics on the must-read list for those interested in the future of the human race." James J. Hughes, Executive Director, Institute for Ethics and Emerging Technologies