Scientists say the mystery of why humans are so right-handed may trace back to our first steps on two legs.
Why do humans overwhelmingly prefer their right hand while other primates do not? Scientists have debated that question for decades, but a new study suggests the answer may be rooted in two defining moments of human evolution: learning to walk upright and developing much larger brains.
About 90% of people worldwide are right-handed, making humans unique among primates. No other ape or monkey species shows such a strong population-wide preference for one hand. Researchers have long explored possible explanations involving genetics, brain structure, tool use, and development, yet the origins of human handedness have remained uncertain.
Now, researchers from the University of Oxford say they may have uncovered a major piece of the puzzle.
Upright Walking and Human Handedness
The study, published in PLOS Biology, was led by Dr. Thomas A. Püschel and Rachel M. Hurwitz from Oxford’s School of Anthropology and Museum Ethnography, along with Professor Chris Venditti from the University of Reading.
The team analyzed data from 2,025 individuals representing 41 monkey and ape species. Using Bayesian models that accounted for evolutionary relationships among species, the researchers tested several leading theories about how handedness evolved.
They examined possible influences including tool use, diet, habitat, body mass, social behavior, brain size, and movement patterns.
At first, humans appeared to stand completely apart from the trends seen in other primates. But when researchers added two additional factors into their models, brain size and the relative length of arms compared to legs, humans no longer looked like such an evolutionary outlier.
The arm-to-leg ratio is widely used as a marker of bipedal locomotion, or upright walking. According to the researchers, the findings suggest that larger brains and walking on two legs together may explain why humans developed such an unusually strong preference for the right hand.
How Handedness Changed Through Human Evolution
The researchers also used their models to estimate handedness in extinct human ancestors.
Their results suggest that early hominins such as Ardipithecus and Australopithecus probably showed only modest right-hand preferences, similar to those seen in modern great apes.
That changed with the emergence of the genus Homo. Species including Homo ergaster, Homo erectus, and Neanderthals appear to have developed increasingly strong right-hand preferences over time. In modern Homo sapiens, that trend eventually reached the extreme right-hand dominance seen today.
One species stood out as an exception: Homo floresiensis, the small-bodied human relative often called the “hobbit” species.
Researchers predicted that Homo floresiensis likely had a much weaker preference for the right hand. They believe this matches the species’ anatomy, which combined a relatively small brain with adaptations for both climbing and upright walking rather than fully specialized bipedal movement.
Bigger Brains May Have Strengthened Right-Hand Bias
The findings point to a two-stage evolutionary process.
First, upright walking freed the hands from locomotion, allowing them to be used more for manipulating objects and performing specialized tasks. Later, as human brains grew larger and became more complex, the tendency toward right-handedness became much stronger and eventually spread across nearly the entire population.
Dr. Thomas A. Püschel, Wendy James Associate Professor in Evolutionary Anthropology at the University of Oxford, said: “This is the first study to test several of the major hypotheses for human handedness in a single framework. Our results suggest it is probably tied to some of the key features that make us human, especially walking upright and the evolution of larger brains. By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human.”
Why Left-Handedness Still Exists
The study also raises new questions that scientists hope to explore in the future.
Researchers still do not know exactly why left-handedness has continued to persist throughout human evolution or how human culture may have helped reinforce widespread right-handedness over time.
The team also noted that similar limb preferences in animals such as parrots and kangaroos could point to broader evolutionary patterns shared across very different species.
Reference: “Bipedalism and brain expansion explain human handedness” by Thomas A. Püschel, Rachel M. Hurwitz and Chris Venditti, 27 April 2026, PLOS Biology.
DOI: 10.1371/journal.pbio.3003771
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