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... But a new study by neurologists at the University of California, Los Angeles and Johns Hopkins University suggests that arm dominance is much more to do with practice than something innate within the brain.

"Limb dominance is often taken as evidence that the dominant hemisphere is intrinsically better at motor control," write Ahmet Arac, Nicolas Jeong Lee, and John Krakauer, in a paper published in Proceedings of the National Academy of Sciences.

"We tested an alternative: dominance reflects asymmetric practice with tools and objects requiring precise control of complex trajectory shapes."

Since most people have already been using their dominant hand loyally throughout their lives, it's difficult to design an experiment to test this hypothesis.

Arac and colleagues came up with a clever way to control for existing dominance, though: making people write with their elbows, something most people have probably never attempted, let alone practiced, before. ...