Asked by: Mark Reynolds, Milton Keynes
One simple answer is that handedness runs in families and is known to be inherited. Scientists have recently found a network of genes that is responsible for body asymmetry and also influences handedness. The deeper question is why about 90 per cent of people are right-handed and only 10 per cent left-handed. In other species that show a hand (or paw) preference, including chimpanzees, polar bears, dogs and cats, the split is about equal.
One theory relates handedness to language, because most people’s language centres are in the left hemisphere. Another is that in a mainly right-handed culture, being left-handed might give a small advantage in outwitting an opponent. This may explain the success of many left-handers at the top level in such sports as fencing, tennis and cricket. Working against this is the value of cooperation, which is easier when everyone is right-handed. So these combined pressures might explain the stable 90:10 split.