Around 90% of humans are right-handed, a trait not widely shared with other primates. A 2026 study published in PLOS Biology analyzed 41 primate species to understand why humans show such strong right-hand dominance. Researchers found that two key factors—larger brain size and the shift to bipedal locomotion—are the most likely drivers of this evolutionary trend. Walking upright freed the hands for fine motor tasks, and over time, natural selection may have favored individuals with consistent hand preference, especially as brain organization evolved.

The study suggests that early hominins like Ardipithecus ramidus and Australopithecus afarensis already showed mild right-hand preferences, which grew stronger in later species such as Homo erectus and Neanderthals. Homo sapiens now show the strongest bias, while Homo floresiensis is an exception, likely due to its small brain and mixed climbing behavior. The findings highlight how anatomy and brain development shaped a uniquely human trait.

Left-handedness, present in about 10% of people, appears tied to brain asymmetry formed before birth. Genetic factors, such as rare variants of the TUBB4B gene, may play a role, though some cases may stem from random developmental variation. Scientists are also exploring whether similar limb preferences in animals like parrots and kangaroos—often linked to upright posture—reflect the same evolutionary pressures.