Around 90 per cent of people are right-handed. Researchers believe the answer is because of two areas of human evolution. The first is walking on two legs; the other is our large brain. When humans first walked on two legs, their hands were free to do many things. We started doing many things with our hands. If most people used the same hand, it was easier to do things like use tools, hunt, cook, and work together.

Scientists wondered why only humans are largely right-handed, but monkeys use both hands equally. The researchers compared human behaviour with monkey behaviour. The research showed that humans have longer legs compared to their arms. 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."