Artificial intelligence has become the pet anxiety of luminaries like Elon Musk, Bill Gates, and Stephen Hawking. They have all expressed concerns about our Promethean quest to develop machine intelligence, and those concerns seem to be spreading every day. But there's another dimension of technological change that ought to worry us every bit as much as AI, if not more so. Bioengineering has already allowed human beings to take control of their own evolution. Whether it's emergent cloning technologies or advanced gene therapy, we're quickly approaching a world in which humans can -- and will -- change the way they live and die. Michael Bess is a historian of science at Vanderbilt University and the author of a fascinating new book, Our Grandchildren Redesigned: Life in a Bioengineered Society. Bess's book offers a sweeping look at our genetically modified future, a future as terrifying as it is promising. "We're going to give ourselves a power that we may not have the wisdom to control very well," he told me.

They met for the first time in a hotel bar at Lake Tahoe in 1998, one evening after a technology conference. Bill Joy was an eminent computer-systems designer, chief scientist for Sun Microsystems. Ray Kurzweil was an award-winning inventor and technologist, whose many creations included a reading machine for the blind and an advanced music synthesizer. Their conversation focused on the future relationship between humans and machines. What they saw that evening, as they gazed together into the coming decades, was something that has come to be called the Singularity.