Why are most of humans right-handed?


Between 70 and 90% of human beings are right-handed, regardless of geographical area. But why are left-handed people under-represented?

Since the work of Paul Broca in 1877, we know that the brain functions asymmetrically for certain tasks, and that the control of movements is contralateral. Indeed, the motor skills of the left side of the body are governed by the right hemisphere, and vice versa. The fact of being right- or left-handed also concerns animals, such as amphibians, whales, rodents, and marsupials. For example, the majority of chimpanzees and gorillas are right-handed, while in cats lateralization seems to depend on gender: male individuals would rather be left-handed while females would prefer their right side.

Lateralization is partly genetically determined, so we can wonder if being right-handed could have an evolutionary advantage. One explanation would be that having the same laterality as the majority of its congeners would allow to use tools made by others. Indeed, some stone tools made 1.5 million years ago already seem to show that right-handed people were already more widespread in prehistoric times.

Interestingly, a small portion of the general population (3 to 4%) is considered ambidextrous. In children with autism spectrum disorder (ASD), they represent between 17 and 47%. Since motor difficulties appear as early as 7 months of age in children with ASD, this type of symptom could allow for earlier diagnosis and management.