Why is almost everyone right-handed? The answer may lie in how we learned to walk

Humans sat conspicuously outside the pattern that explained every other primate, but when the researchers added two factors into the model - brain size and the relative length of our arms versus our legs (a standard anatomical marker of bipedal locomotion) - that exceptional status disappeared. In other words, once you account for upright walking and a large brain, humans stop looking like an evolutionary anomaly.Using the same models, the team was also able to estimate likely handedness in extinct human ancestors. The picture that emerges is a gradient; early hominins such as Ardipithecus and Australopithecus probably had only mild rightward preferences, broadly similar to modern great apes. With the appearance of the genus Homo, the bias strengthens markedly - through Homo ergaster, Homo erectus and Neanderthals - reaching its modern extreme in Homo sapiens.There is one striking exception: Homo floresiensis, the small-brained “hobbit” species from Indonesia, shows a much weaker predicted preference. The researchers suggest this fits the wider pattern: floresiensis had a small brain and a body adapted to a mix of upright walking and climbing, rather than full bipedalism.The findings point to a two-stage story. Walking upright came first, freeing the hands from the work of locomotion and creating new selective pressure for fine, lateralised manual behaviours. Larger brains came later, and as they grew and reorganised, the rightward bias hardened into the near-universal pattern seen today.The study leaves open questions for future research, including the role of cumulative human culture in stabilising right-handedness, why left-handedness has persisted at all, and whether similar patterns of limb preference seen in animals such as parrots and kangaroos point to a deeper, convergent story across the wider animal kingdom.Read 'Bipedalism and brain expansion explain human handedness' in full in PLOS Biology.For more information about this story or republishing this content, please contact [email protected]