By making people write with their elbows, scientists found that repetition really matters

Babies are born with a natural preference for using their left or right side. Now, a new study suggests that preference alone doesn’t explain the dominant side’s superior skills: They come from practice.

Then, Arac, of the David Geffen School of Medicine at UCLA, and his colleagues threw these folks a curveball by asking them to write with a pen taped to an elbow. Half the people wrote with their dominant elbow, and the other half wrote with their nondominant elbow. Neither elbow — dominant or nondominant — was very good.

Yet practice made all the difference. After a new group of 12 people put pen-equipped elbow to paper for a few hours, their writing improved — and it improved equally for both dominant and nondominant elbows. By finding symmetrical improvements in the elbow, the new study helps make the case that practice matters. Dominance, the researchers write, “is a practice effect.”

Most of the participants were right-handed. A study focused on lefties would be interesting, Arac says, as would exploring different sorts of body movements. Scientists also want to understand “what enables better or faster learning,” Arac says, particularly for people as they relearn certain movements.