A major new study compared hand preferences across more than 2,000 primates from 41 species.
About 90% of humans are right-handed, and now scientists think they know why. A major new study compared hand preferences across more than 2,000 primates from 41 species. Unlike humans, most primates don’t strongly favor one hand across their whole species — some lean left, some right, and many show no clear pattern at all. Humans stand out as a major exception. Scientists think two big changes in human evolution — walking upright and growing larger brains — may explain why most people are right-handed. The idea is that walking upright freed our hands for tasks like tool use, encouraging individuals to specialize. Later, as human brains grew larger, that preference tipped strongly toward the right hand across the whole population.