Around 90% of people across all cultures are right-handed, a trait so common it masks a deep evolutionary mystery. A new study from the University of Oxford suggests this overwhelming bias emerged not from culture or a single gene, but from two major shifts in human evolution: bipedalism and brain expansion. By analyzing hand preference in 41 primate species, researchers found that traits like tool use or diet didn’t predict handedness—but larger brains and longer legs relative to arms did.

The freeing of hands through upright walking allowed for more specialized use, while brain reorganization in early Homo species like Homo erectus and Neanderthals reinforced right-hand dominance. The study traces a gradual intensification: early hominins like Australopithecus showed only a slight right-hand lean, similar to great apes today, but the preference strengthened through the Homo lineage.

One notable exception is Homo floresiensis, the small-bodied 'hobbit' human from Indonesia, which showed a weaker right-hand bias, likely due to its smaller brain and mixed locomotion. Scientists still debate why left-handedness persists at all, and how cultural factors may sustain handedness patterns. The findings were published in PLOS Biology.