Lateralization of the human brain.

It is often suggested that cerebral asymmetry, when a consistent direction of asymmetry prevails, is unique to humans. We now know that many other species exhibit directionally consistent cerebral and behavioral asymmetries. Nevertheless, the predominance of left-cerebral dominance for language and manual functions may have played a special role in human evolution, even though precursors may be found in other animals-and especially in the great apes. I argue that the common cerebral asymmetry for these functions derives from the origins of language in manual gestures. These, in turn, may originate in specialized circuits for grasping that have been identified in primates, and lateralization may have been progressively introduced as praxic and linguistic functions became more complex.