Monkey Lip Smacks Provide New Insights Into the Evolution of Human Speech
By -- - SCIENCE DAILY
Added: Sun, 03 Jun 2012 22:49:34 UTC
Scientists have traditionally sought the evolutionary origins of human speech in primate vocalizations, such as monkey coos or chimpanzee hoots. But unlike these primate calls, human speech is produced using rapid, controlled movements of the tongue, lips and jaw. Speech is also learned, while primate vocalizations are mostly innately structured. New research published in Current Biology by W. Tecumseh Fitch, Head of the Department of Cognitive Biology at the University of Vienna, supports the idea that human speech evolved less from vocalizations than from communicative facial gestures.
Researchers at Princeton and the University of Vienna used x-ray movies to investigate lip-smacking gestures in macaque monkeys. Lip smacks are made by many monkey species in friendly, face-to-face situations (e.g. between mothers and their infants). Although lip-smacking makes a quiet sound (similar to "p p p p"), it is not accompanied by phonation, which is produced by vocal cord vibration in the "voice box" or larynx.
Although superficially lip-smacking appears to involve simply rapid opening and closing of the lips, the x-ray movies show that lip-smacking is actually a complex behaviour, requiring rapid, coordinated movements of the lips, jaw, tongue and the hyoid bone (which provides the supporting skeleton for the larynx and tongue). Furthermore these movements occur at a rate of about 5 cycles per second, the same as speech, and are much faster than chewing movements (about 2.5 cycles per second). Thus, although lip smacking superficially resembles "fake chewing," it is in fact very different, and more like speech.
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