The promise of eternal youth is both tantalizingly close and far-fetched in this fascinating primer on longevity research. Pulitzer Prizewinning science writer Weiner (The Beak of the Finch) focuses on amateur gerontologist and oddball visionary Aubrey de Grey, a charismatic motormouth who has won a respectful scientific hearing for his argument that we will soon achieve life spans of thousands of years. (His immortality program starts with the removal of a gunky cellular buildup called lipofuscin.) Weiner takes readers on an engrossing tour of cutting-edge research, while citing established life-cycle experts like Shakespeare and Yeats, and he has a knack for translating science into evocative metaphor. He tempers the "prolongevist" optimism with some daunting reality: evolution never engineered humans to last forever, the bodys myriad modes of decay may make that goal impossible, and reaching it, he speculates, might render us morbidly averse to risk or even to having children. Weiners erudite, elegant exposition of the underlying science is stimulating yet sobering