Ancient Roots of Human Right-Handedness Unveiled by New Evolutionary Study

Oxford and Reading researchers meta-analysed handedness in 41 primate species (>2,000 individuals). Phylogenetic models showed a right-hand bias unique to *Homo sapiens*. The East Javan langur (*Trachypithecus auratus*) had a stronger bias; orangutans and snub-nosed monkeys showed slight left preferences. For extinct hominins, *Australopithecus afarensis* had a right tendency, while *H. ergaster*, *H. erectus* and Neanderthals showed stronger biases, Neanderthals second to humans. *H. floresiensis* displayed a weak bias similar to chimpanzees.

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Archaeological data (2016) show right-handedness 1.8 million years ago. Earlier theories linked it to tool use, arboreal locomotion, or brain size. The new analysis tested these ideas together, finding strongest links with encephalization and limb proportions.

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The study was led by evolutionary anthropologist Thomas Püschel of Oxford University, with collaborators from the University of Reading; it appears in *PLOS Biology*.

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Sample: >2,000 individuals from 41 primates. Right-hand bias peaks in *Homo sapiens*, second in Neanderthals. Correlates: brain volume, longer lower limbs. Exceptions: East Javan langur (right), orangutans and snub-nosed monkeys (left), *H. floresiensis* (minimal).

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The authors propose a two-stage model: bipedalism freed forelimbs for manual specialization; later brain growth reinforced right-hand lateralization. Cultural transmission may have amplified the pattern.

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Thomas Püschel emphasized that the research uniquely tests several major handedness hypotheses together and that cross-species comparison clarifies which patterns are ancient versus uniquely human. He also highlighted the potential role of culture in amplifying the right-handedness trajectory.

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The scientists acknowledge unanswered questions, including why left-handed individuals persist and whether comparable lateralization patterns occur in other limb-biased species such as parrots or kangaroos.

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• “This is the first study to test several of the major hypotheses for human handedness in a single framework,” — Thomas Püschel, Evolutionary Anthropologist, Oxford University

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• “By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human.” — Thomas Püschel, Evolutionary Anthropologist, Oxford University

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• “The initial locomotor change prompted by bipedalism can be seen as providing ecological and anatomical opportunities for manual specialization, while encephalization may have later reinforced and further canalized population-level patterns of lateralization,” — Researchers, *PLOS Biology*

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• “Furthermore, culture may have acted concurrently with or amplified the effects of this emerging trajectory of hominin right-handedness.” — Researchers, *PLOS Biology*

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The findings tie bipedalism and brain growth to handedness, illuminating neural lateralization and cultural spread of right-handed norms.

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Future work will address why left-handedness persists and test for similar lateralization patterns in other limb-biased animals.

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