Humans are mostly right-handed, a trait not seen in other primates. Scientists have wondered why for a long time. A new study suggests the answer might be linked to two big changes in human evolution: learning to walk on two legs and developing much larger brains.
About 90% of people worldwide are right-handed. No other ape or monkey species shows such a strong preference for one hand. Researchers have looked at genetics, brain structure, tool use, and development, but the reason for human handedness was still a mystery.
Now, researchers from the University of Oxford believe they have found a key part of the answer.
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Start Your News DetoxUpright Walking and Handedness
The study, published in PLOS Biology, was led by Dr. Thomas A. Püschel and Rachel M. Hurwitz from Oxford, along with Professor Chris Venditti from the University of Reading.
The team looked at data from 2,025 individuals across 41 monkey and ape species. They used special models to understand how handedness evolved, considering how species are related.
They checked for influences like tool use, diet, habitat, body size, social behavior, brain size, and how animals move.
At first, humans seemed very different from other primates. But when the researchers added two more factors to their models—brain size and the length of arms compared to legs—humans fit in better.
The arm-to-leg ratio is a common sign of walking on two legs. The findings suggest that bigger brains and walking upright together might explain why humans developed such a strong right-hand preference.
How Handedness Changed Over Time
The researchers also used their models to guess the handedness of early human ancestors.
Their results suggest that early hominins like Ardipithecus and Australopithecus probably had only a slight right-hand preference, similar to today's great apes.
This changed with the Homo genus. Species like Homo ergaster, Homo erectus, and Neanderthals seemed to develop stronger right-hand preferences over time. In modern Homo sapiens, this trend led to the extreme right-hand dominance we see today.
One species was an exception: Homo floresiensis, often called the "hobbit" species.
Researchers predicted that Homo floresiensis likely had a much weaker right-hand preference. They believe this matches the species' body, which had a relatively small brain and could both climb and walk upright, rather than being fully specialized for walking on two legs.
Bigger Brains and Right-Hand Bias
The findings point to a two-step evolutionary process.
First, walking upright freed the hands from moving, allowing them to be used more for handling objects and special tasks. Later, as human brains grew larger and more complex, the tendency toward right-handedness became much stronger. It eventually spread across almost the entire human population.
Püschel, an associate professor at the University of Oxford, said this is the first study to test several major ideas about human handedness at once. He noted that the results suggest it's linked to key human traits, especially walking upright and bigger brains. By studying many primate species, scientists can understand which parts of handedness are old and shared, and which are unique to humans.
Why Left-Handedness Still Exists
The study also brings up new questions for future research.
Scientists still don't know exactly why left-handedness has continued throughout human evolution. They also wonder how human culture might have helped strengthen widespread right-handedness over time.
The team also noted that similar limb preferences in animals like parrots and kangaroos could show broader evolutionary patterns across very different species.
Deep Dive & References
Bipedalism and brain expansion explain human handedness - PLOS Biology, 2026
