Ambidexterity emerges from a tangle of genetic variants, brain wiring, prenatal chemistry, and sometimes deliberate practice. No single “ambidexterity gene” has been found, but a 2020 genome-wide study of nearly 1.8 million people identified seven distinct genetic regions linked to it, all pointing toward the central nervous system and the way the brain’s hemispheres divide labor.1PubMed Central. Genome-wide association study identifies 48 common genetic variants associated with handedness That finding alone tells you something important: the roots of ambidexterity are partly shared with handedness in general but partly distinct, involving its own biology and likely its own developmental story.
How Rare Is True Ambidexterity
Most people overestimate how many truly ambidextrous individuals exist. In a large UK Biobank study of over half a million people, about 89% reported being right-handed, 9.3% left-handed, and only 1.7% said they used both hands equally.2PubMed Central. A large-scale population study of early life factors influencing left-handedness That 1.7% figure, though, depends heavily on how you ask the question. When researchers use more detailed assessments that test performance across many tasks rather than asking a single self-report question, the picture shifts. One study using fine-grained skill testing found about 3.3% of participants qualified as ambidextrous, while a much larger group, roughly 29%, fell into a “mixed-handed” category where they used different hands for different activities without being equally skilled with both.3PubMed. How should “ambidexterity” be estimated?
That distinction between ambidexterity and mixed-handedness matters for everything that follows. Someone who writes with their right hand but throws a ball with their left is mixed-handed, not ambidextrous. A person who can write, throw, and eat with either hand at comparable skill levels is closer to what researchers mean by true ambidexterity. Handedness research has historically lumped these groups together or ignored mixed-handers entirely, which has muddied the science considerably. A recent commentary in laterality research argued that mixed-handedness should be recognized as a distinct and central category rather than being folded into either right- or left-handedness, since misclassifying these people has skewed findings for decades.1PubMed Central. Genome-wide association study identifies 48 common genetic variants associated with handedness
The Genetic Landscape
If you are ambidextrous, your genes played a role, but not a deterministic one. The largest genetic study on handedness to date pooled data from the UK Biobank, 23andMe, and the International Handedness Consortium. Across nearly 1.77 million participants, the researchers found 41 genetic regions associated with left-handedness and 7 associated with ambidexterity specifically.1PubMed Central. Genome-wide association study identifies 48 common genetic variants associated with handedness The fact that ambidexterity had its own set of associated regions, partially overlapping with but distinct from those linked to left-handedness, suggests that ambidexterity is not simply “incomplete” left-handedness or some midpoint on a spectrum. It has its own genetic signature.
These genetic regions do not code for hand preference directly. Instead, they cluster around pathways involved in brain development, particularly the regulation of microtubules, the structural scaffolding inside cells that helps organize the growing brain. The tissue-enrichment analysis in the same study pointed squarely at the central nervous system, meaning the genetic influence on handedness works primarily through how the brain gets built, not through the muscles or bones of the hands themselves.1PubMed Central. Genome-wide association study identifies 48 common genetic variants associated with handedness
Replication work in other populations has found some of the same signals. A genome-wide study in a Korean cohort identified 15 genetic loci associated with ambidexterity, and one of those loci, near the gene ANKIB1, replicated a finding from earlier European datasets.4PubMed Central. Genome-wide association and replication studies for handedness in a Korean community-based cohort Seeing the same genetic variants turn up across different ethnic backgrounds strengthens the case that these are real biological signals rather than statistical flukes.
What Twin Studies Reveal About Heritability
Genetics sets the stage for handedness, but it does not write the entire script. Twin studies are one of the cleanest ways to tease apart genes from environment, and they paint a nuanced picture. A meta-analysis of twin studies found that identical twins were slightly more likely to share the same handedness than fraternal twins, with an odds ratio of about 1.11 for handedness concordance.5PubMed Central. Handedness in twins: meta-analyses That number is statistically meaningful, but it is small. If handedness were strongly genetic in the way eye color is, you would see identical twins matching far more often.
The same meta-analysis found something else that is underappreciated: twins in general, both identical and fraternal, are more likely to be left-handed than singletons, with an odds ratio of about 1.40 for left-handedness. But for mixed-handedness specifically, the twin-versus-singleton difference was negligible.5PubMed Central. Handedness in twins: meta-analyses The elevated left-handedness in twins is thought to relate to prenatal conditions like crowding in the womb or birth stress, factors that could push brain lateralization in atypical directions. The fact that mixed-handedness does not show the same twin elevation hints that its causes may be somewhat different from those driving left-handedness.
Beyond DNA Sequence
Genes are not the whole story on the molecular level, either. Epigenetics, the system of chemical tags that controls when and where genes are active without changing the DNA sequence itself, appears to play a significant role. Researchers have found that asymmetric patterns of DNA methylation in the fetal spinal cord influence asymmetric gene expression, accounting for roughly a quarter of the variation in left-versus-right gene activity at just eight weeks after conception.6eLife. Epigenetic regulation of lateralized fetal spinal gene expression underlies hemispheric asymmetries These spinal cord asymmetries emerge before the brain’s motor cortex has even connected to the spinal cord, suggesting that some of the earliest groundwork for hand preference is laid down through epigenetic mechanisms acting locally in the body.
A broader review of the topic concluded that particular asymmetries in DNA methylation can affect gene expression in the central nervous system in ways that ultimately shape handedness.7PubMed. Beyond the genome-Towards an epigenetic understanding of handedness ontogenesis Research on methylation patterns in peripheral tissues of adults has also observed differences linked to hand preference, and because hand movements and other lateralized behaviors begin in the womb, researchers expect these methylation differences to emerge very early in development.8Scientific Reports. DNA methylation in peripheral tissues and left-handedness For ambidextrous individuals, whose lateralization is by definition less pronounced, these early molecular asymmetries may simply be weaker or more balanced.
Prenatal Hormones and the Developing Brain
Another influence that acts before birth is hormonal. Prenatal testosterone exposure has long been linked to variations in brain lateralization and handedness. The evidence comes partly from digit ratio studies, which use the relative length of the index and ring fingers as an indirect marker of fetal testosterone levels. A study comparing left- and right-handed males found that left-handers showed digit ratio patterns consistent with higher prenatal testosterone exposure.9PubMed. Finger length ratio (2D:4D) in left- and right-handed males Prenatal testosterone has been linked not just to handedness but to a range of traits including spatial skills and cognitive profiles.10PubMed Central. 2D:4D Ratio and its Implications in Medicine
The proposed mechanism goes something like this: testosterone in the womb influences the rate at which the two brain hemispheres mature. Higher levels may slow the development of the left hemisphere relative to the right, which could push the developing brain toward less rigid lateralization. Less rigid lateralization, in turn, could make someone more likely to develop left-handedness or, in some cases, ambidexterity. This is still a hypothesis with ongoing debate, but it fits with the broader observation that people whose brains are less strongly lateralized tend to have more varied hand preferences.
How the Brain Is Wired Differently
The most visible structural difference in the brains of ambidextrous people involves the corpus callosum, the thick cable of nerve fibers that connects the left and right hemispheres. A landmark study found that the corpus callosum was about 11% larger in left-handed and ambidextrous people compared to consistent right-handers.11PubMed. The brain connection: the corpus callosum is larger in left-handers A bigger corpus callosum means more cross-talk between the hemispheres. In a strongly right-handed person, the left hemisphere typically dominates motor control and language. In an ambidextrous person, both hemispheres appear to share responsibilities more evenly, and the larger information highway between them supports that sharing.
Language is one area where this reduced lateralization shows up clearly. Brain imaging studies have found that about 22% of left-handed and ambidextrous individuals show atypical language lateralization, meaning language is either shared between hemispheres or concentrated in the right hemisphere, compared to only 4 to 6% of right-handers.12PubMed. Language lateralization in left-handed and ambidextrous people: fMRI data This does not mean ambidextrous people process language worse; it means their brains organize the task differently. The functional consequences of that different organization are a separate question, and one where the evidence gets complicated.
Ambidexterity and Cognitive Performance
There is a persistent myth that ambidextrous people are cognitively gifted because they “use both sides of the brain.” The research does not support this. A meta-analysis examining handedness and cognitive ability found that when people are simply sorted into left-handers and right-handers, no meaningful differences in cognitive performance emerge.13PubMed. Handedness and cognitive ability: Using meta-analysis to make sense of the data But when ambidextrous or mixed-handed individuals are examined as a separate group, a different pattern appears. A study using a large nationally representative dataset found that ambidextrous individuals performed more poorly than either left- or right-handers on tests measuring arithmetic, memory, and reasoning, and this pattern held in both children and adults.14PubMed. Handedness and intellectual achievement: an even-handed look
Before anyone reads too much into that: the effect sizes are small, and the relationship appears to be more complex than a simple “ambidexterity equals cognitive disadvantage.” A reanalysis of the same underlying data using continuous measures of relative hand skill rather than categorical groupings found a more nuanced picture, suggesting the relationship between hand preference and cognitive ability is not as straightforward as earlier work implied.15PubMed. Cognitive ability and continuous measures of relative hand skill: a note It is possible that some of the apparent cognitive disadvantage in ambidextrous individuals reflects the muddled way researchers have defined the category rather than a real underlying difference. When you lump together people who are naturally skilled with both hands, people who are weakly handed in either direction, and people who are mixed-handed for different tasks, you are not studying a single phenomenon.
Links to Neurodevelopmental and Psychiatric Conditions
One area where ambidexterity and mixed-handedness attract clinical attention is their elevated prevalence in certain psychiatric and neurodevelopmental conditions. A synthesis of the research found that non-right-handedness, which includes both left-handedness and mixed-handedness, appears at higher rates among people with neurodevelopmental disorders.16PubMed Central. Non-right-handedness and psychiatric disorders: A synthesis of epidemiological, genetic, and neurobiological evidence The link is especially well-documented for schizophrenia. One study found that mixed-handedness was about five times more common among people with schizophrenia than among controls, and the rate showed a stepwise increase from controls to first-degree relatives to patients themselves, suggesting a genetic component to the association.17PubMed. Schizophrenic patients and their first-degree relatives show an excess of mixed-handedness
These findings do not mean that being ambidextrous is itself a disorder or that ambidextrous people are at high risk for schizophrenia. The vast majority of ambidextrous and mixed-handed people have no psychiatric diagnosis. What the research suggests is that the same developmental processes that influence hemispheric lateralization can, when they go significantly awry, contribute to both atypical handedness and vulnerability to certain conditions. One theoretical framework proposes that when a particular genetic variant leaves hemispheric dominance to chance, the result can be a lack of clear cerebral dominance, which in most people just produces mixed or ambidextrous hand preference but in a small subset may contribute to disordered thought patterns and, at the same time, possibly to enhanced creativity and lateral thinking.18PubMed. Ambidexterity and magical ideation
Can You Train Yourself to Be Ambidextrous
Given that genetics and prenatal development seem to lay the foundation, you might wonder whether ambidexterity can be acquired through practice. The short answer is that you can substantially improve your non-dominant hand’s skill, but the brain does not simply mirror itself in the process. A training study using brain imaging found that when right-handed people practiced precision drawing with their left hand, the improvements were associated with increased connectivity between sensorimotor hand areas and a network in the left hemisphere involved in skilled hand movements.19PubMed Central. Increased functional connectivity between cortical hand areas and praxis network associated with training-related improvements in non-dominant hand precision drawing In other words, the brain recruited additional resources from an existing network rather than building a new mirror-image system.
Another study examining a technique called intermanual transfer, where you practice a skill with one hand to improve the other, found significant motor improvements in the non-dominant hand along with changes in a distributed brain network involving the supplementary motor area, thalamus, basal ganglia, and cerebellum.20PubMed. Neuroplastic and motor behavioral changes after intermanual transfer training of non-dominant hand: A prospective fMRI study The brain is clearly plastic enough to allow substantial gains in non-dominant hand performance. But trained ambidexterity and innate ambidexterity are probably not the same thing neurologically. A person who practices using their left hand for years develops stronger connections and recruits motor planning networks more efficiently, but their fundamental hemispheric architecture remains that of a right-handed person who has learned a new skill.
This distinction matters for people who encounter advice about training children to use both hands or cross-training athletes to switch-hit. Practice will produce real improvements, and for specific sports or musical instruments, it may be worth pursuing. But the idea that training both hands equally will rewire the brain into a state comparable to natural ambidexterity is not well supported. The neuroplastic changes are genuine but operate on top of existing lateralization rather than replacing it.
Why Handedness Exists at All
To understand ambidexterity, it helps to step back and ask why the vast majority of humans are right-handed in the first place. This is actually a harder question than it sounds. A review of the evolutionary origins of handedness evaluated several competing hypotheses, including that population-level right-handedness emerged from the demands of skilled tool use, communicative gestures, hierarchically organized actions, or intentional goal-directed behavior.21PubMed Central. Evolutionary origins of human handedness: evaluating contrasting hypotheses None of these hypotheses has won decisively, and the authors concluded that the old simple distinction between human and animal handedness is no longer tenable.
A large comparative study across primate species muddied the waters further. Contrary to the assumption that right-handedness is a deep primate trait, most non-human primate species showed no strong population-level hand preference, and a slight majority actually leaned left.22eLife. The evolution and biological correlates of hand preferences in anthropoid primates The strong rightward bias we see in humans may be relatively recent in evolutionary terms, tightly linked to the expansion of language and complex tool manufacture that characterize our species. If that is the case, then ambidextrous individuals may represent a persistent minority phenotype, one that sticks around because the genetic variants underlying reduced lateralization carry other effects, both beneficial and costly, that prevent natural selection from eliminating them entirely.
How Handedness Gets Measured, and Why It Matters
A surprising amount of confusion about ambidexterity traces back to how researchers measure handedness in the first place. The most commonly used tool for decades has been the Edinburgh Handedness Inventory, a questionnaire that asks which hand you prefer for ten common activities. Your responses are combined into a single score that places you somewhere on a continuum from strongly left-handed to strongly right-handed, with people near the middle classified as ambidextrous or mixed-handed. The problem is that this captures preference but not performance. You might say you use your right hand for writing and your left for opening jars, but that tells us nothing about how skilled you are with each hand at either task.
Studies that measure actual manual performance, asking participants to do timed tasks with each hand separately, consistently find more mixed-handers and fewer truly ambidextrous individuals than preference-based surveys suggest. The 3.3% ambidexterity rate found in performance-based testing versus the roughly 1.7% found in self-report illustrates this gap.3PubMed. How should “ambidexterity” be estimated? 2PubMed Central. A large-scale population study of early life factors influencing left-handedness The numbers move in opposite directions depending on the tool you use, which means any claim about “what percentage of people are ambidextrous” depends entirely on how you define and measure it.
This measurement problem has practical consequences for research. If studies classify ambidextrous people as left-handers, as many do by default, then findings about “left-handers” may actually reflect the ambidextrous people mixed into the group. If studies exclude everyone who is not clearly right- or left-handed, they throw out the very population most interesting for understanding brain lateralization. The push to treat mixed-handedness as its own legitimate category rather than a messy in-between is not just a matter of academic tidiness. It changes what the data tell us about cognition, mental health, and brain organization.
Stroke Recovery and Hemispheric Flexibility
One practical area where handedness and brain lateralization matter is recovery from stroke. When a stroke damages the hemisphere that controls a person’s dominant hand, rehabilitation depends partly on how much the undamaged hemisphere can compensate. Handedness has been identified as one of several patient-related factors that influence prognosis for post-stroke language recovery.23PubMed Central. Post-stroke aphasia prognosis: a review of patient-related and stroke-related factors The reasoning is that people with less lateralized brains, including ambidextrous and left-handed individuals, may have more bilateral language representation to begin with, giving the intact hemisphere a head start in taking over lost functions. This is speculative and not yet well proven in large clinical studies, but it aligns with the brain imaging data showing that ambidextrous individuals are far more likely to have language distributed across both hemispheres rather than concentrated in one.
The flip side of this coin is that strong lateralization, the neurological basis of strong handedness, may be efficient precisely because it avoids duplication. Having one hemisphere specialize in language and fine motor control while the other handles spatial processing and attention could make both functions work better than they would in a brain trying to do everything on both sides. This efficiency-versus-resilience tradeoff is one reason researchers suspect ambidexterity has persisted in the population at low frequencies rather than being selected away entirely. For most people in most situations, strong lateralization works well. But in the aftermath of brain injury, a more bilateral brain may have an edge.