BEIJING -- For centuries, scientists have grappled with a striking human puzzle — why roughly 90 percent of people worldwide are right-handed — yet the underlying cause of handedness has long remained elusive, until now, as a Chinese research team says to have solved it.

Published recently online in the Journal of Genetics and Genomics, the study, led by researchers from the Chinese Academy of Sciences (CAS), has revealed how hand preference develops through animal experiments, proposing the "Hypothesis of Acquired Conservation of Right-Hand Preference" to address the question of handedness origins, one of the most challenging puzzles in science.

The research team found that untrained mice use both paws equally when eating, with no specific preference. In the experiment, the scientists designed a special cage with a small hole placed in a challenging position, so that the mice had to use a specific paw to reach the food inside.

This allowed the scientists to force the mice to eat using only their left paw or only their right paw.

Remarkably, after just 5 to 7 forced feeding trials, the mice developed a lasting preference. Those trained to use their right paw became "right-pawed," continuing to favor that paw for over a month even after restrictions were lifted. The same held true for mice trained to use their left paw, proving that limb preference can be acquired through training.

A crucial finding emerged in a follow-up experiment. After the mice formed a habit with one paw, scientists forced them to switch. Right-paw habits proved persistent and hard to change, whereas left-paw preferences could be more easily "corrected" to right-paw use.

Even when mice were forced to alternate between paws, most ended up favoring their right paw. Only a small minority remained "stubborn" left-paw users, reproducing the real-world distribution of human handedness.

Based on these results, the researchers concluded that human handedness is not innate, but rapidly established during early life through repeated unilateral hand use.

"A right-hand preference, once formed, is more stable and easier to sustain than a left-hand one, granting it a cumulative advantage in individual development. Reinforced by a right-hand-dominant social environment, this tendency ultimately creates our 'right-handed world,'" said Sun Zhongsheng, a researcher from the Institute of Zoology at the CAS.

The findings not only resolve a longstanding behavioral puzzle but also offer a new perspective for understanding brain asymmetry and the plasticity of human behavioral traits.