Asked by: Kirsty Findlay, Aberdeen
Nobody knows for sure. Some animals prefer using one eye, leg or paw, but we’re unusual in that over 90 per cent of us are right-handed. One theory is that since we alone have language, which requires fine motor skills, it makes sense for the same half of the brain to control speech and motor function. So the left hemisphere of right-handed people’s brains will control speech and motion. Yet about half of left-handers have language on the left, as most people do, and they cope perfectly well, so this can’t be the whole story. Nor does it explain why we don’t have a 50/50 split of right- and left-handers.
Perhaps whole societies benefit if everyone uses the same hand, but then a few rebels might gain an advantage. This may be why left-handers excel at tennis, cricket, fencing and boxing, having the advantage of unfamiliarity over the majority right-handers. Left-handers have often been reviled, but perhaps our left-handed ancestors won enough fights to keep a certain proportion of left-handedness in the human population.