Among primates, humans stand alone as the species where a handedness bias is nearly universal across the entire population. A fresh study, conducted by Oxford specialists and featured in the journal PLOS Biology, connects this phenomenon to bipedalism and the increase in brain size.
Roughly 90% of humans, spanning all cultures, favor their right hand, yet no other primate species exhibits such a dominant skew. Decades of research into the brain, genetics, and evolution have failed to yield a conclusive explanation for why the vast majority of humans lean toward being right-handed.
The research team gathered data from 2025 individuals across 41 monkey species, including the great apes. Utilizing Bayesian modeling, which accounts for the evolutionary relationships between species, the investigators tested fundamental hypotheses regarding the origin of right-handedness.
Humans initially appeared as an anomaly compared to all other primates, but by incorporating variables like brain size and the ratio of arm to leg length (as standard anatomical indicators of upright walking), this unique human status was neutralized within the model.
Applying the same models, the research unit managed to estimate the degree of right-handedness present in human ancestors. It was determined that early hominins, such as Ardipithecus and Australopithecus, displayed only a slight right-hand lean, similar to modern great apes. With the advent of the genus Homo, this preference substantially intensified—becoming more pronounced in Homo ergaster, Homo erectus, and Neanderthals, peaking in Homo sapiens.
However, there is one surprising outlier: Homo floresiensis, the “Hobbit” species from Indonesia, shows a far less defined preference. Experts, though, find a pattern here too: H. floresiensis possessed a smaller brain, and their bodies were adapted more for climbing and upright walking than full-fledged bipedalism.
The evidence suggests a two-stage evolutionary process. Initially, bipedalism emerged, freeing the hands from locomotion. Subsequently, a larger brain developed, and during the growth and reorganization of this organ, right-sided asymmetry became fixed.
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