The story begins with a scientist, Dr. Yorkshire Bell, noting that dinosaurs once flourished and became extinct when they advanced beyond their ability to adapt to change. Giant mammals, such as the saber-toothed tiger and the mammoth, came and went the same way. Humans, Earth's current dominant life form, had one special asset – intelligence – enabling them to advance further than all creatures before them. Dr. Bell wondered if, one day, humans might advance beyond the point of no return and render themselves extinct.