The dominant hand is the preferred hand an individual uses for complex, fine motor tasks requiring high dexterity, such as writing, eating, or throwing a ball. This preference, known as handedness, results in one hand being consistently stronger, faster, and more coordinated than the other. The hand used less often is called the non-dominant hand. Handedness is an established trait that develops early in life.
The Spectrum of Handedness
Handedness exists on a continuum, though it is most commonly categorized into three main groups. Right-handedness is the most common classification, representing approximately 90% of the global population. This preference means the right hand is consistently chosen for tasks requiring precision and skill. Left-handedness accounts for the remaining 10% of people, who naturally favor their left hand for intricate movements.
Variations beyond a simple right or left preference are also recognized, though they are much less common. Ambidexterity describes the rare ability to perform any task equally well with either hand, occurring naturally in about 1% of the population. A different classification is mixed-handedness, or cross-dominance, where an individual prefers a different hand for different tasks, such as writing with the right hand but throwing with the left. Mixed-handedness is estimated to be about as widespread as left-handedness.
The Role of Genetics and Development
The origin of hand preference is a complex trait influenced by both genetic and developmental components. While no single “handedness gene” exists, familial patterns suggest heredity plays a role. Twin studies estimate that genetic factors account for about 25% of the variation. Research indicates that hand preference is likely influenced by the combined effect of multiple genes, possibly up to 40, each contributing a small effect.
These genetic influences are related to the establishment of the body’s overall right-left asymmetry during early development. Environmental factors also contribute to the remaining variation. Developmental influences begin before birth, as fetal thumb-sucking preferences observed in the womb often predict later handedness. Consistent motor practice and social learning solidify the preference throughout infancy and early childhood.
Neurological Basis: Brain Lateralization
The physical manifestation of handedness reflects functional specialization within the brain, known as cerebral lateralization. The brain’s motor control system is contralateral: the left hemisphere primarily controls the right side of the body, and the right hemisphere controls the left side. Consequently, right-handedness is an expression of the left cerebral hemisphere’s dominance for motor function.
The left hemisphere is also dominant for language processing in the vast majority of people, including most left-handed individuals. This overlap between the brain areas controlling fine motor skills and those governing language is one reason for the high prevalence of right-handedness in humans. In left-handed individuals, the pattern of lateralization for both motor control and language is often more varied.
Functional magnetic resonance imaging (fMRI) studies show that while both right- and left-handers share similar brain activation patterns for simple movements, they differ when performing sequential tasks. Left-handers tend to activate larger volumes of brain areas and show less lateralization during these tasks compared to right-handers. This suggests that the brains of left-handed people may distribute motor control more broadly across both hemispheres.