- Humans show a 90% right-hand preference, unlike other primates with near-zero bias
- Study analyzed 2,025 primates across 41 species to compare hand preferences
- Human right-hand bias linked to upright walking and larger brain size traits
About 90% of people across cultures are "righty," favouring their right hand. This is one of the strongest behavioural patterns in humans, but it has left many scientists intrigued, the New York Post reported. A new study suggests the answer isn't in our hands at all; it's apparently in our legs and our brains. Researchers from the University of Oxford and the University of Reading analysed data from 2,025 monkeys and apes across 41 different species. While some primates like spider monkeys and langurs show individual hand preferences, humans are unique.
On the Mean Handedness Index, where positive numbers indicate right-hand bias, humans score 0.76, which is dramatically higher than other primates, which cluster near zero.
"Humans display a pronounced right-handed bias which contrasts sharply with the phylogenetic prediction," the authors mentioned in the study published in PLOS Biology.
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The team tested major theories for handedness, including diet, habitat, body mass, social structures, tool use, and locomotion. Humans remained outliers in every case.
But when researchers added two factors to their models - brain size and the ‘intermembral index,' which compares arm length to leg length, the human exception disappeared entirely.
Humans have unusually long legs compared with arms, a hallmark of walking upright. Once those two traits were included, our strong right-hand bias fit the broader primate pattern.
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"This is the first study to test several of the major hypotheses for human handedness in a single framework," researcher Dr Thomas A. Puschel said in the study said as quoted..
"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."
The scientists believe that "proper walking allowed increasingly specialised use of one hand over the other." Tree-dwelling species often show stronger hand preferences because moving through branches requires precise movements. Humans may have taken that pattern in a different direction.
Also, the link between handedness and human evolution isn't new. A 1.8-million-year-old Homo habilis jawbone from Tanzania shows right-slanting striations on the front teeth, likely made when processing materials with the right hand.
Archaeological evidence also shows humans have strongly favoured the right hand for tool use for at least half a million years.
