Scientists Finally Cracked Why Almost Everyone Is Right-Handed

Around 90 percent of people across every culture on earth prefer their right hand, a level of consistency so unusual that no other primate species comes close to matching it, and scientists have spent decades trying to figure out why. A new study from the University of Oxford, published in PLOS Biology, may finally have the answer, and it comes down to two of the most defining moments in human evolutionary history: the day our ancestors stood up on two legs, and the long process by which the human brain grew dramatically larger and more complex. Researchers analyzed data from over 2,000 monkeys and apes across 41 primate species and used sophisticated modeling to test every major theory about the origins of handedness, from diet and tool use to social structure and habitat. When they added brain size and a measure of upright walking into their models, humans stopped being an evolutionary mystery entirely.

The study suggests the process happened in two distinct stages over millions of years. First, walking upright freed the hands from the task of moving the body around, creating new pressures that pushed our ancestors toward using one hand more consistently and skillfully than the other. Then, as the brain expanded and became more specialized across its two halves, the preference for the right hand grew significantly stronger and more universal. By tracing the pattern back through extinct human relatives, the researchers found that early ancestors like Australopithecus probably had only a mild right-hand preference similar to modern great apes, while later species including Homo erectus and Neanderthals showed a steadily strengthening bias that eventually became the near-universal trait seen in people today. The lead researcher at Oxford called it the first study to rigorously test the major competing theories of handedness, and said the findings suggest that what feels like a simple personal preference is actually written into the deepest chapters of what made us human.

Source:https://www.sciencedaily.com/releases/2026/05/260517211429.htm