People Aren’t Born as Righties or Lefties—They Develop Hand Dominance With Practice, a New Study Suggests

Humans do have a biological preference for using one side of their body, which might prime them for using limbs on that side for complex motor tasks like writing—and honing those skills over time

Margherita Bassi | Daily Correspondent

July 22, 2026 12:59 p.m.

Share

Copy linkEmailSMSFacebookXRedditLinkedInBlueskyPrint

Add as preferred source

Many people assume that they are born either left-handed or right-handed. New research, however, suggests that part of handedness actually comes down to practice.

While you do have a biological preference for using one side of your body, your dominant hand’s improved skills at tasks like writing compared to those of your other hand were developed over time, researchers reported on June 30 in the journal Proceedings of the National Academy of Sciences. That means you can level up your nondominant limb’s abilities through training—something occasionally experienced by stroke survivors and amputees.   

“You don’t prefer your dominant hand because it’s more skilled. It becomes more skilled because you prefer it,” study co-author John Krakauer, a neuroscientist at Johns Hopkins University School of Medicine, says in a statement. “You wouldn’t notice any difference between your two hands without tools and objects in the world that demand practice to use well.”

Roughly 90 percent of people are righties, a trait largely attributed to evolution. However, genetics aren’t the only factor at play. Two left-handed parents, for example, have a left-handed kid just 25 to 30 percent of the time, reports Quanta’s Natalie Wolchover. And the identical twin of a lefty has only a 20 to 30 percent chance of also showing left dominance.

Previous research suggests that preference for using one side of the body develops in the womb, but for decades, scientists have debated why the preferred side is usually more skilled. One major theory posits that the brain hemisphere that controls the preferred side of the body is wired to manipulate movement more effectively than the other hemisphere. Another idea, however, is that improved ability on one side is accumulated over time because those limbs are favored.

To investigate, Krakauer and his colleagues asked roughly two dozen right-handed participants to reach their arms toward a target, touching it with the palm. Some of them also did the task with four-pound wrist weights or with a thin bamboo stick—a tool—extending from their forearm, in which they used the stick to tap the target. Across participants, both arms performed equally at the first two tasks, but in the stick test, their dominant limb tended to perform better.

In another experiment, 11 people wrote the letter A and the number 8 with both their dominant and nondominant hands as neatly and quickly as possible. As expected, they did better with the dominant side. But then, they did the same task with a marker attached to their elbows, and neither side was better. A different group of 12 participants was asked to do the elbow writing exercise for a few hours, and both their dominant and nondominant limbs improved at the same rate, suggesting that both limbs could acquire the skill with practice.

“The dominant arm isn’t more capable because one hemisphere of the brain is simply better at controlling movement,” study co-author Ahmet Arac, a neurologist at the David Geffen School of Medicine at the University of California, Los Angeles, says in a separate statement. “It is because we’ve spent a lifetime practicing the specific, complicated movements that tools and handwriting demand. Take away that practice by switching to a body part like the elbow that’s never done the task before and the advantage disappears.”

The findings track with the proposal that hand dominance is often passed down because we generally learn complicated motor skills from other people—who are often righties.  

For instance, “a dad might explain to his kid how to tie their shoes. That’s of course easier if the dad uses the same hand for explaining the kid uses for tying the shoe themselves,” said Sebastian Ocklenburg, a psychologist at MSH Medical School in Germany who was not involved in the study, to Kim Mills on the American Psychological Association’s “Speaking of Psychology” podcast last year. “So, there seems to be a benefit from having the same handedness as other people because it makes this motor learning easier, which is one of the ideas why there are so many right-handers.”

In the future, Arac says he hopes to see more research focusing on the minority handedness group—lefties—as well as other kinds of body movements, he tells Science News’ Laura Sanders. It would also be interesting to know “what enables better or faster learning,” he adds.

Margherita Bassi | Read More

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.