Ambidexterity

How it works

About 90% of people are right-handed². One common theory links handedness to the way the two halves of the brain divide up fine motor control. The evidence for it is mixed². Signs of it can be seen before birth, and it settles in early childhood².

Genes play a part but not a large one. Twin studies put the inherited share at about 25%, with the rest coming from development and environment². A 2020 study of more than 1.7 million people found 48 genetic variants linked to handedness. Of these, 41 were tied to left-handedness and 7 to ambidexterity⁵.

True ambidexterity means equal skill with both hands for every task, including writing. Mixed-handedness is much more common. A mixed-handed person might write with the left hand and do everything else with the right³. Many people who call themselves ambidextrous are mixed-handed.

The non-dominant hand can be trained. Musicians, surgeons, and athletes do it on purpose. People who injure their writing hand can learn to write with the other, but it takes practice. The trained hand rarely reaches full equality.

How common it is

The often-quoted figure of about 1%¹ comes from one study of nearly 8,000 children⁶. Two large self-report surveys found about 2% and 3%⁵. Researchers do not test the same tasks or use the same cutoff for “equal skill”, so estimates shift with the method. Counting only writing gives a low number. Counting many everyday tasks, and calling someone ambidextrous if they split evenly across most of them, gives a higher one. No country runs a standard national test for it.

Try it

1. Write your name with your usual hand, then with the other. Compare.
2. List five tasks: throwing a ball, using scissors, brushing teeth, opening a jar, dealing cards.
3. Note which hand you reach for in each one without thinking.
4. If the answers are all the same hand, you are strongly one-handed. If they split, you are mixed-handed. If both hands do every task equally well, you are in the rare group.

Is it a problem?

No. Ambidexterity is not a disorder and needs no treatment. One large study found that mixed-handed children were twice as likely to have language and school difficulties⁶. A hand preference that changes suddenly in an adult, rather than being lifelong, is worth mentioning to a doctor, since a sudden shift can follow injury to the brain or the writing arm.

History and culture

The word comes from Latin: ambi, both, and dexter, right. It means having two right hands¹. Leonardo da Vinci wrote with his left hand in mirror script and is often described as ambidextrous⁴.