The primate isolation call and the evolution and physiological control of human speech
pp. 301-321
in: Jan Wind, Brunetto Chiarelli, Bernard Bichakjian, Alberto Nocentini, Abraham Jonker (eds), Language origin, Berlin, Springer, 1992Abstract
The search for the common roots of the vocalizations of humans and nonhuman primates may come initially through the study of the sounds of infants. Emotional expression through sound is very similar in the infants of all primates, including humans. This has been most thoroughly documented for the distress sounds of the infant separated from its caregiver ("isolation call"). While the isolation calls (IC) of different primate species share overall acoustic characteristics (each expiratory unit consisting of a gradually modulated tone with little noise and frequency modulation), there are more detailed accoustic differences that reliably identify the species. With maturation, the IC becomes differentiated to subserve commumicative functions besides signalling separation distress. The production mechanisms of the IC of human and nonhuman primates may also share a common origin. The anterior cingulate gyrus, part of the limbic forebrain, is essential for normal production of the IC in adult primates, as well as for normal speech in adult humans. The widely accepted homology between the cry of the human neonate and the IC of other mammals suggests that the neural substrate mediating this vocal behavior may have had a conservative evolutionary history. A plausible evolutionary scenario by which the primate IC became linked to human speech may come from the evidence for functional differentiation, wherein the infant IC develops into an array of sounds used in group communication, mediated by the increased cognitive capacity of early hominids.