From Bill McKibben, the bestselling author of The End of Nature, comes a powerful and passionate intellectual sequel about humanity's final threshold. We are about to cross the line from born to made, from created to built. Sometime in the next few years, some scientist will reprogram a human egg or sperm cell, sparking a genetic change that will be passed on down into eternity. We are sleepwalking toward the future, argues McKibben, and it's time to open our eyes. In The End of Nature, nearly fifteen years ago, McKibben demonstrated how humanity had begun to irrevocably alter-and endanger-our climate and environment, on a global scale. Now he turns his eye from the very big to the very small, to the cellular world-and asks us to stop and consider the irreversible changes we are making to the human condition. He ranges from the frontiers of scientific experimentation to the very foundations of ethical, cultural, and spiritual thought. He delineates the difference between therapy and engineering, showing how we have made the transition from repair to manufacture, from medicine to breeding. Finally, he looks into the not-so-distant future, when genetic science, robotics, and nanotechnology will push against the very door of immortality, and challenges us to confront this most profound question of our existence with care, intelligence, and, ultimately, humility.