From the bestselling author of The End of Nature comes a passionate plea to limit the technologies that could change the very definition of who we areWe are on the verge of crossing the line from born to made, from created to built. Sometime in the next few years, a scientist will reprogram a human egg or sperm cell, spawning a genetic change that could be passed down into eternity. We are sleepwalking toward the future, argues Bill McKibben, and it’s time to open our eyes.In The End of Nature, nearly fifteen years ago, McKibben demonstrated that humanity had begun to irrevocably alter—and endanger—our environment on a global scale. Now he turns his eye to an array of technologies that could change our relationship not with the rest of nature but with ourselves. He explores the frontiers of genetic engineering, robotics, and nanotechnology—all of which we are approaching with astonishing speed—and shows that each threatens to take us past a point of no return. We now stand at a critical threshold, poised between the human past and a post-human future. Ultimately, McKibben offers a celebration of what it means to be human, and a warning that we risk the loss of all meaning if we step across the threshold. His wise and eloquent book argues that we cannot forever grow in reach and power—that we must at last learn how to say, “Enough.”