Why is almost everyone right-handed? Scientists finally SOLVE the mystery - and say the answer may lie in how we learned to walk
It's a mystery that has baffled scientists for years – why is almost everyone right–handed? Across every human culture, only about 10 per cent of people favour their left hand. However, despite decades of research, scientists have remained clueless as to why this is the case. Now, experts from the University of Oxford believe they've solved the mystery. According to their research, the answer comes down to two defining features in human evolution – walking on two legs, and the dramatic expansion of the human brain.'This is the first study to test several of the major hypotheses for human handedness in a single framework,' said Dr Thomas A. Püschel, lead author of the study. '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.' According to the research, the answer comes down to two defining features in human evolution – walking on two legs, and the dramatic expansion of the human brainResearch suggests that around 10–12 per cent of people are left–handed. However, until now, why that figure remains so low has been a mystery. To get to the bottom of it, the researchers analysed data on 2,025 individuals across 41 species of monkeys and apes. Using models that account for evolutionary relationships between species, the team tested several hypotheses for why handedness evolved. This included tool use, diet, habitat, body mass, social organisation, brain size, and locomotion. Their analysis revealed that humans sat 'conspicuously outside the pattern' that explained every other primate. However, when the researchers added brain size and the relative length of our arms versus legs into the model, that exceptional status disappeared.'In other words, once you account for upright walking and a large brain, humans stop looking like an evolutionary anomaly,' the researchers explained. Using the same model, the researchers were also able to estimate the likely handedness of extinct human ancestorsUsing the same model, the researchers were also able to estimate the likely handedness of extinct human ancestors. The results suggest that early species such as Ardipithecus and Australopithecus probably had only mild rightward preferences, similar to modern great apes.However, with the appearance of Homo erectus and Neanderthals, right handedness started to become more prevalent. Interestingly, the researchers found one exception. Homo floresiensis, a 'hobbit' species from Indonesia, had a much weaker preference for right handedness.Why? Because this species had a small brain and used a mix of upright walking and climbing. Piecing everything together, the researchers suggest a two–stage story to explain why most people are right–handed. Firstly, species started walking upright, freeing their hands for other activities. 'The initial adoption of an upright gait freed the upper limbs, creating novel opportunities for tool use, gestural communication, and other fine motor behaviors in which lateralization would have conferred performance advantages,' the team explained in their study, published in PLOS Biology. Next, their brains began to grow and reorganise, hardening the rightward bias. The team added: 'Concurrently, increases in brain size and associated cortical reorganization may have promoted greater hemispheric specialization, thereby enhancing the neural efficiency of such lateralized behaviors.'
