The right is more conservative than the left: a postnatal hypothesis of handedness based on mice.

Handedness is a fundamental behavioral trait in humans, with the majority exhibiting right-hand dominance. While its origins remain elusive, it is considered an innate genetic trait. This study demonstrates pawedness in mice (n = 473), comparable to human handedness, as an acquired trait rapidly emerging after limited unilateral paw training. Notably, acquired right-pawedness demonstrates greater conservativeness compared to left-pawedness, as evidenced by stronger stability and greater resistance to reversal. This results in a population right-paw dominance under random training conditions. Moreover, acquired pawedness also exhibits sex differences, with the initial preference proving more malleable in females. These findings unveil the acquired features of pawedness in mice. By illuminating possible behavioral laterality commonalities across species, the study proposes a postnatal hypothesis for the origins of human handedness: it is not an innate genetic trait as traditionally believed, but rather an environmentally acquired stable behavior whose development is actively guided by genetic predispositions.