Theoretical speculations on the evolutionary origins of hemispheric specialization

ABSTRACT—Hemispheric specialization has long been considered a uniquely human trait associated with the evolution of language and handedness. Recent studies in a host of vertebrate species have reported evidence of population-level behavioral and brain asymmetries, challenging the claims for the uniqueness of hemispheric specialization to the human species. Here we summarize the findings in nonhuman species and discuss the adap-tive significance and potential costs of lateralization of function. Hemispheric specialization refers to sensory, motor, and cog-nitive abilities that are specialized to either the left or right cerebral hemisphere. Two of the most pronounced manifes-tations of hemispheric specialization in humans are right-handedness and left-hemisphere lateralization for languag