Why Are Some People Left-Handed?

About 10% of the global population is left-handed, a ratio that has remained relatively stable across cultures and centuries. Handedness is partly genetic: a child with two left-handed parents has about a 26% chance of being left-handed, compared to 10% for two right-handed parents. However, no single "handedness gene" has been found; it appears to involve multiple genes affecting brain asymmetry. Prenatal hormone exposure, particularly testosterone levels, may also influence which hemisphere of the brain becomes dominant for motor control. An evolutionary theory suggests left-handedness persists because it provides a surprise advantage in combat and competitive sports, where opponents are less accustomed to facing left-handers.