A groundbreaking study published in PLOS Biology suggests that the uniquely human prevalence of right-handedness is fundamentally linked to the evolution of bipedalism and significant brain expansion. The research, which analyzed manual lateralization across 41 anthropoid species, posits that these two evolutionary hallmarks account for why approximately 90% of humans favor their right hand.
The Wall Street Journal highlighted this development, stating in a recent tweet, "Big brains and two-legged walking help explain why humans have dominant hands." This finding addresses a long-standing evolutionary enigma, as no other primate species exhibits such a strong, population-level hand preference. Researchers discovered that while humans are an outlier among primates in handedness, this exceptional status disappears when accounting for brain size and the relative length of arms versus legs, a proxy for bipedal locomotion.
The study, led by researchers including those from Oxford University, indicates a two-stage evolutionary process. Initially, walking upright freed the hands from locomotion, creating new selective pressures for fine, lateralized manual behaviors. Subsequently, as human brains grew and reorganized, this rightward bias became more pronounced, leading to the near-universal pattern observed today. Early hominins, such as Ardipithecus and Australopithecus, likely had only mild rightward preferences, similar to modern great apes. The bias strengthened markedly with the appearance of the genus Homo, reaching its modern extreme in Homo sapiens.
An interesting exception noted was Homo floresiensis, the small-brained "hobbit" species, which showed a much weaker predicted preference. This aligns with the broader pattern, as floresiensis had a smaller brain and a body adapted to a mix of upright walking and climbing, rather than full bipedalism. While the research provides significant insights, it leaves open questions regarding the role of cumulative human culture in stabilizing right-handedness, the persistence of left-handedness, and potential convergent patterns of limb preference in other animals like parrots and kangaroos.
