Why are most people right-handed?

A large majority of human beings are right-handed: it is estimated that 7 to 9 out of 10 people are. This proportion is roughly the same all over the world. Several theories are now trying to explain why left-handed people are so under-represented, but the mechanisms involved are still not fully understood.

Laterality (dominance of the right or left side over the other for the performance of tasks or biological functions) is not unique to humans. In some species, the distribution is almost equal. In cats, it even depends on the sex: males are predominantly left-handed, while females are predominantly right-handed. In some primates, such as the chimpanzee and the gorilla, the majority of individuals are right-handed. But humans are the only ones where the ratio is unbalanced in favour of right-handed individuals.

Being right-handed: an evolutionary advantage?

It is known that genetics play a role in determining whether a person is left- or right-handed. A left-handed couple is more likely to have a left-handed child than a right-handed or mixed couple, but they are still more likely to have a right-handed child than a left-handed one. British researchers have already identified some of the genes involved. But genetics is not the only force at work, and its mechanisms remain poorly identified.

Social or cultural factors can also influence laterality. This idea is the starting point of another theory that could explain why left-handed people are in the minority.

Man has often been described as a social animal, and from an evolutionary point of view, it is more advantageous to adapt to one's community. To live together, share tools and spaces, and better social cooperation, it is also more beneficial to be skilled with the same hand as others. The earliest tools of our ancestors, which are more than 3 million years old, do not seem to indicate any particular bias in the distribution between right and left-handed people. It is, therefore, possible to assume that over time, one side won the evolutionary game so that individuals could more easily use tools made by others.

Left-handed people more represented in top-level sport

The question that is arising is why the right side is the one that has prevailed over the left? One hypothesis comes from how the brain works and its laterality: the left hemisphere controls the right side of the body and vice versa. We also know that language is one of the asymmetrical functions since, in most people, the area responsible for language is located in the left hemisphere. Those phenomena would lead to increased use of the left hemisphere and, thus, a preference for the right side. However, the link is not so simple since the language area is not systematically in the left hemisphere in 100% of right-handed people and is also on the left in most left-handed people.

These theories may lead one to wonder why left-handed people did not simply disappear with evolution. One explanation is that being left-handed confers certain advantages, especially in combat, as it adds an unexpected factor. In some sports, such as fencing, table tennis, badminton or tennis, left-handed people are significantly more represented than the general population.