Around 90 per cent of people are right-handed. Scientists have spent years trying to find out why. Researchers in the UK believe the answer is because of two areas of human evolution. The first is walking on two legs; the other is the large size of our brain. When humans first walked on two legs, their hands were free to do things. Our brain worked out many things to do with our hands. If most people used the same hand, using tools and working with other people became easier. It was useful for doing things like hunting and cooking.

Scientists wondered why only humans are largely right-handed. Monkeys and apes use both hands equally. The researchers compared human behaviour and brain patterns with monkeys and apes. The research showed that humans have longer legs compared to their arm length. Another reason is the left side of the brain controls the right hand. It is responsible for coordination. A researcher said: "By looking across many primate species, we can begin to understand which aspects of handedness are ancient and shared, and which are uniquely human."