Or Poul Anderson's Brainwave (1953), in which the Earth finally leaves a part of the galaxy which inadvertently made thinking hard. And everything with two neu

Or Poul Anderson's Brainwave (1953), in which the Earth finally leaves a part of the galaxy which inadvertently made thinking hard. And everything with two neurons to rub together gets smarter, not just humans. Essentially, we evolved in what Vinge would later call "The Unthinking Depths" (if memory serves) to deal with the strain.