March 12, 2007

The evolution of human speech

CURRENT ANTHROPOLOGY Volume 48, Number 1, February 2007

The Evolution of Human Speech
Its Anatomical and Neural Bases

by Philip Lieberman

Human speech involves species-specific anatomy deriving from the descent of the tongue into the pharynx. The human tongue's shape and position yields the 1:1 oral-to-pharyngeal proportions of the supralaryngeal vocal tract. Speech also requires a brain that can "reiterate"—freely reorder a finite set of motor gestures to form a potentially infinite number of words and sentences. The end points of the evolutionary process are clear. The chimpanzee lacks a supralaryngeal vocal tract capable of producing the "quantal" sounds which facilitate both speech production and perception and a brain that can reiterate the phonetic contrasts apparent in its fixed vocalizations. The traditional Broca-Wernicke brain-language theory is incorrect; neural circuits linking regions of the cortex with the basal ganglia and other subcortical structures regulate motor control, including speech production, as well as cognitive processes including syntax. The dating of the FOXP2 gene, which governs the embryonic development of these subcortical structures, provides an insight on the evolution of speech and language. The starting points for human speech and language were perhaps walking and running. However, fully human speech anatomy first appears in the fossil record in the Upper Paleolithic (about 50,000 years ago) and is absent in both Neanderthals and earlier humans.


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