Stephen Hawking's final work, "Brief Answers to the Big Questions", which tackles issues from the existence of God to the potential for time travel, was released on Monday by his children, who helped complete the book after his death. Hawking feared a race of “superhumans” capable of manipulating their own evolution. He says the human race had to improve its mental and physical qualities, but a genetically-modified race with greater memory capacity and disease resistance would endanger others.