The psychology of handedness and brain asymmetry

Overview

Handedness results from a mix of genetics, prenatal factors, and environment, with left-handed people forming a persistent minority (about 10.6%). It arises from brain hemispheric dominance for fine motor actions, and about 25% of this trait is genetically inherited across many genes involved in brain development rather than the hands themselves. In early life handedness is often already set, sometimes before birth, and ambidexterity is extremely rare. Stereotypes linking left-handedness with higher creativity do not hold up to scientific testing. The conversation also touches on how handedness manifests across animals, why left-handers are underrepresented in brain research, and what this means for science and clinical practice.

Prevalence and Variation in Handedness

The largest meta-analyses estimate that around 10.6% of people are left-handed, with country differences largely shaped by culture and schooling norms like handedness retraining. In some places left-hand writing has been discouraged, lowering observed rates, while countries with less retraining show higher left-handed prevalence. There are no countries where left-handers exceed 20%, underscoring handedness as a minority trait across populations.

“handedness is a quite complicated thing.” - Dr. Sebastian Ocklenburg

Genetic and Environmental Influences

Genetic factors contribute to roughly a quarter of handedness, and large studies identify about 48 genes that influence brain development rather than the hands themselves. The brain’s motor cortex shows hemispheric dominance linked to handedness, with left-handers typically relying on the right motor cortex and right-handers on the left. Prenatal factors, hormones, and early life experiences also play roles, alongside demographic patterns such as sex differences in handedness.

“the actual amount of handedness that can be explained by these genetic factors is around a quarter, so 25% of handedness basically is genetic, and we know it is not one gene, it’s about 48 different genes that play a role.” - Dr. Sebastian Ocklenburg

Birth and Development of Handedness and Ambidexterity

Handedness often emerges before birth, and researchers can predict laterality with high accuracy from prenatal markers such as thumb-sucking and limb interaction observed in ultrasound. By around age 6, when writing begins, the preferred hand is usually established for many individuals. Although some people show mixed-handed patterns, true ambidexterity—equal speed and accuracy with both hands—is extremely rare, estimated at about 0.1% of the population.

“handedness is already pretty much determined at birth or even before.” - Dr. Sebastian Ocklenburg

Research Representation, Stereotypes, and Sports

Left-handers are underrepresented in brain and psychology research, which risks biasing results and clinical applications that rely on laterality. In sports, left-handed athletes can have a competitive edge in racket and combat sports due to rarity and opponents’ relative unfamiliarity, though this is largely a situational advantage rather than an overall talent difference. The discussion also notes that stereotypes about left-handed creativity are not supported by controlled studies, even as beliefs persist in popular culture.

“left-handed people are often underrepresented in brain research” - Dr. Sebastian Ocklenburg