Language, Handedness, and Primate Brains: Did the Australopithecines Sign?

Abstract

Evidence from comparative primate neuroanatomy, archaeology, and studies of vocalization systems of nonhuman primates suggests that human vocal language has a long evolutionary history and that there is continuity between our early primate ancestors' call systems and human speech. Old World monkeys exhibit cerebral asymmetries similar to those that appear related to human language. If arboreal monkeylike ancestors of humans were also characterized by cerebral asymmetry, then the fundamental asymmetry that forms the neurological substrate for human language may have been established through selection for simple “discrete” call systems in an arboreal habitat and would have occurred much longer ago than previously thought. The eventual shift from an arboreal to a terrestrial habitat was accompanied by increased complexity (“gradation”) of vocal communication systems. The archaeological record of tools suggests that communication systems became still more complex under the selective pressures that led to bipedalism and that language had been selected for by the time that bipedalism was achieved. Contrary to the gestural hypothesis, right‐handedness (which could not have preceded freeing of the hands) succeeded speech and may have been due to selective pressures for increased complexity of communication, causing a Field Effect upon the brain. [australopithecine, cerebral asymmetry, language, primate brains, right‐handedness]