There’s a stereotype that left-handed people are clumsier, but that might have something to do with the fact that they live in a world of objects optimized for the right-handed: scissors, the computer mouse, surgical tools, and guns, to name a few. The discrimination against the 12 percent of the population who are lefties has disarming historical roots. In the Middle Ages, left-handed writers were said to be the devil’s voice boxes, and the Jewish scholar Maimonides included sinistrality in his list of 100 imperfections that should preclude someone from priesthood.