Ambidexterity is the ability to use both hands with equal skill and comfort. It’s one of the rarest hand-preference traits in humans, occurring in roughly 1% of the population. The other 99% break down to about 90% right-handed and 10% left-handed. While many people can do certain tasks with their non-dominant hand, true ambidexterity means having no clear preference for either hand across a wide range of activities.
Ambidexterity vs. Mixed-Handedness
These two terms often get confused, but they describe different things. A truly ambidextrous person performs all tasks with roughly equal ability in both hands. A mixed-handed (or cross-dominant) person switches hands depending on the task: they might write with their left hand but throw a ball with their right. Mixed-handedness is considerably more common than true ambidexterity, and researchers treat them as separate categories when studying hand preference.
The distinction matters because self-reports don’t always match actual performance. Studies have found that when people are tested on specific tasks, their faster or more accurate hand isn’t always the one they call their dominant hand. Someone who considers themselves ambidextrous may actually show a measurable preference when their performance is tracked carefully.
How Handedness Is Measured
The most widely used tool is the Edinburgh Handedness Inventory, a questionnaire that asks which hand you prefer for ten everyday activities like writing, throwing, using scissors, and striking a match. Each response is scored, and the results produce a number called a Laterality Quotient ranging from -100 (completely left-handed) to +100 (completely right-handed). A score between -40 and +40 classifies someone as ambidextrous. Scores above +40 indicate right-handedness, and scores below -40 indicate left-handedness.
What’s Different in the Brain
Handedness is closely tied to how the brain’s two hemispheres divide labor. In strongly right-handed or left-handed people, one hemisphere dominates motor control for skilled hand movements. In ambidextrous individuals, this dominance is weaker, and the two hemispheres share the workload more evenly.
That sharing shows up physically. The corpus callosum, the thick band of nerve fibers connecting the brain’s two halves, tends to be thicker in people with weaker hand preference. Researchers at multiple institutions have found significant negative correlations between the degree of hand preference and corpus callosum thickness: the less lateralized someone’s handedness, the thicker the connection between hemispheres. This pattern is especially pronounced in the regions of the corpus callosum responsible for transferring motor information between the two sides of the brain. The leading explanation is straightforward: when both hemispheres are actively involved in hand control, they need a larger communication channel between them.
This reduced lateralization doesn’t stop at motor skills. Ambidextrous people and others with weak hand preference also tend to be less lateralized for language processing. In strongly right-handed people, language is typically concentrated in the left hemisphere. In ambidextrous individuals, language functions are more distributed across both hemispheres.
Genetics and Heritability
Handedness runs in families, but not in a simple, predictable pattern. A large-scale analysis combining data from 35 twin studies estimated that genetic factors account for about 25% of the variation in handedness. The remaining 75% comes from environmental factors, prenatal conditions, and random developmental variation.
For decades, researchers worked with models proposing a single gene that biases people toward right-handedness, with a second version of that gene leaving handedness up to chance. These models fit population-level data well, but when scientists actually searched for the gene, they couldn’t find it. Large genome-wide studies have identified 48 common genetic variants associated with handedness, but each one has only a small effect. There is no single “handedness gene.” Instead, hand preference appears to emerge from the combined influence of many genes, each contributing a tiny nudge, layered on top of non-genetic factors.
Links to Neurodevelopmental Conditions
Mixed-handedness and ambidexterity have drawn attention from researchers studying conditions like ADHD and dyslexia, though the connections are nuanced. For dyslexia, one notable finding is that mixed-handedness was more than twice as common among people with dyslexia (11.7%) compared to control groups (5.4%). The difference in the proportion of mixed-handers alone accounted for the overall handedness distribution differences between the groups.
For ADHD, the picture is less clear. Some studies have proposed left-handedness or non-right-handedness as a risk factor, while others have failed to confirm any association. Mixed-handedness has also been studied in relation to developmental coordination disorder, where the proportion of mixed and ambidextrous handedness appears elevated compared to dyslexia groups. These correlations don’t mean ambidexterity causes any of these conditions. Rather, reduced hemispheric lateralization may be a shared feature of certain neurodevelopmental profiles.
Can You Train Yourself to Be Ambidextrous?
The brain is remarkably adaptable, and training your non-dominant hand does produce measurable changes. In a neuroimaging study that tracked people practicing skilled tasks with their non-dominant hand, participants showed significant motor improvement compared to a control group. Brain scans revealed that the learning process engaged an expanding network over time: early training relied mainly on the brain’s outer cortical motor areas (a more conscious, deliberate form of learning), while later stages recruited deeper subcortical structures involved in automatic, procedural movement. In other words, skills transferred to the non-dominant hand gradually shifted from effortful to fluid.
That said, training one hand doesn’t produce the same thing as natural ambidexterity. A person who practices writing with their non-dominant hand can improve significantly, but they’re building a new skill on top of an already lateralized brain. Naturally ambidextrous individuals develop without strong lateralization from the start, which is a fundamentally different neurological trajectory.
Famous Examples
Leonardo da Vinci is perhaps the most well-known ambidextrous figure in history. Art historians long suspected he could use both hands, and in 2019, researchers at Florence’s Uffizi Gallery confirmed it through handwriting analysis. They studied da Vinci’s earliest surviving work, a drawing of the Arno River from 1473. The front inscription was written in his famous mirror script (right to left, characteristic of left-hand writing), while the back inscription was written left to right in a well-formed style consistent with right-hand use. Both inscriptions shared enough key features to confirm they were written by the same person. According to art historian Cecilia Frosinini, da Vinci was born left-handed but was trained as a young child to use his right hand, a common practice at the time. He maintained skilled use of both hands throughout his life, though he may have lost use of his right hand later due to nerve damage.