Why Are Most People Right-Handed?

About nine in ten people prefer their right hand. Roughly 85–90% of people are right-handed, 10–15% are left-handed, and a small minority are ambidextrous. This imbalance is found worldwide: no human population has been shown to have a majority of left-handers, indicating that both biological and cultural factors are at play.

Early Development: the bias begins before birth

Research shows hand preference often appears well before a baby is born. Ultrasound studies indicate that by around the 10th week of gestation most fetuses move the right arm more frequently than the left, and by about the 15th week many prefer sucking the right thumb. These early patterns suggest that right-handedness is a default outcome of brain development for most people.

Genetics and chance

Handedness is not controlled by a single "handedness gene." Instead, dozens of genes — perhaps as many as 40 — influence brain development in ways that typically bias motor control toward the right hand. These genes guide neural architecture and lateralization, but they do not determine handedness with absolute certainty. Random variations during embryonic brain development — for example, chance fluctuations in molecular concentrations at critical moments — can lead to left-handedness even in the absence of strong genetic or environmental causes.

Cultural influences

Culture can shape which hand people use. In some parts of Asia, the Arab world, and Africa the left hand is considered unclean for social or religious reasons, and children may be encouraged or coerced to use their right hand for eating, writing, and other tasks. Such social pressure lowers the reported rates of left-handedness in affected communities, but even where no cultural bias exists left-handers remain a minority, supporting the idea of an underlying biological tendency.

Evolutionary explanations

Scientists have proposed several evolutionary reasons for the prevalence of right-handedness. One idea links the bias to tool use and the transmission of skilled manual behaviors: archaeological evidence suggests humans have favored the right hand for tool use for at least half a million years. Another hypothesis relates to combat: in face-to-face fighting with edged weapons, a right-handed attacker is more likely to strike an opponent's left chest — potentially affecting survival over many generations. These pressures could have reinforced a right-hand majority.

Why left-handers persist

Left-handers may enjoy situational advantages because they are rare. In one-on-one sports and combat, their actions can be less predictable to predominantly right-handed opponents, which can translate into performance benefits. This frequency-dependent advantage helps keep left-handers at a stable, lower proportion in populations.

Conclusion

The predominance of right-handedness likely results from a complex mix of genetic influences, early developmental processes, cultural practices, and evolutionary pressures such as tool use and combat. While many genes bias brain development toward the right hand, chance developmental events and cultural factors produce and shape left-handedness. Researchers continue to study how these forces interact to produce the consistent global pattern.

Experts quoted: Paul Rodway, Senior Lecturer in Psychology, University of Chester; Clyde Francks, Professor of Brain Imaging Genomics, Max Planck Institute and Radboud University Medical Center.