Why 90% of humans are right-handed may be linked to walking upright, new study finds

About 90 per cent of humans across cultures favour their right hand, making handedness one of the most striking and enduring traits in human evolution. No other primate species displays such a strong population-wide preference, leaving scientists puzzled for decades over why humans became overwhelmingly right-handed. Now, a new study led by researchers at the University of Oxford suggests the explanation may lie in two defining features of human evolution: walking upright and the growth of larger brains.

Study compares more than 2,000 primates

Published in PLOS Biology, the research analysed data from 2,025 individuals across 41 species of monkeys and apes. According to phys.org the study was led by Dr Thomas A. Püschel and Rachel M Hurwitz from Oxford’s School of Anthropology and Museum Ethnography, alongside Professor Chris Venditti from the University of Reading. Using Bayesian evolutionary modelling, the researchers tested several theories linked to handedness, including tool use, diet, habitat, body mass, social organisation, brain size and movement patterns.

Humans initially appeared to be a major evolutionary outlier. But once the researchers included two variables, brain size and the ratio between arm and leg length, which reflects upright walking, humans no longer stood apart from other primates.

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Walking upright may have changed human hands

The findings suggest bipedalism may have been the first major turning point. As early humans began walking on two legs, their hands were freed from locomotion, allowing more specialised and coordinated manual activity. The researchers believe larger brains later strengthened this preference, gradually turning a mild tendency into the near-universal right-handedness seen today.

“This is the first study to test several of the major hypotheses for human handedness in a single framework,” Dr Püschel said. “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.”

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Clues from extinct human ancestors

The team also estimated handedness patterns in extinct human relatives. Early hominins such as Ardipithecus and Australopithecus likely showed only weak right-handed preferences, similar to modern great apes. The bias appears to strengthen significantly with the emergence of the Homo genus, including Homo erectus, Homo ergaster and Neanderthals, before reaching modern levels in Homo sapiens.

One exception was Homo floresiensis, the small-bodied ‘hobbit’ species discovered in Indonesia. Researchers predicted weaker handedness in the species, linking it to its smaller brain and mixed climbing and walking adaptations.

The study does not fully explain why left-handedness has persisted in humans or whether culture later reinforced right-handed behaviour. Researchers also say similar limb preferences observed in animals such as parrots and kangaroos could point to broader evolutionary patterns across species.