Michael C. Corballis
This article explores the origins of language in manual gestures. Humans have the capacity to produce complex intentional gestures either vocally or manually and either system can serve as the medium for language. Vocal learning is especially critical to speech, and few non-human primate species appear capable of more than limited vocal learning. Studies suggest that primate calls show limited modifiability, but its basis remains unclear, and it is apparent in subtle changes within call types rather than the generation of new call types. The discovery of mirror neurons in area F5 of primate prefrontal cortex further supports the evolutionary priority of manual gesture. The hands and arms would lend themselves naturally to mimed representation of events in bipedal hominins. Mime is fundamentally imitative, in that there is a mapping between the mimed action and what it represents. Modern signed languages retain a strong mimetic, or iconic, component such as in Italian sign language some 50% of hand signs and 67% of the bodily locations of signs stem from iconic representations. The addition of phonation, perhaps through selection for a FOXP2 mutation, would allow non-visible gestures within the mouth, including movements of the larynx, velum and tongue, to be recovered from the acoustic signal, as proposed by the motor theory of speech perception.
This article focuses on two roles of gesture and explores the changes that take place in the manual modality when it is employed to fulfill the functions of language on its own. Gestures reflect a global-synthetic image. Gesture is idiosyncratic and constructed at the moment of speaking and it does not belong to a conventional code. The gesture conveys nuances of the coastline that are difficult to capture in speech. Gesture allows speakers to convey thoughts that may not easily fit into the categorical system, which are offered by conventional language. The gestures that accompany speech are not composed of parts but instead have parts that derive from wholes that are represented by way of imagery. The imagistic base of gesture allows it to capture and reveal information that speakers may have difficulty expressing in speech. Gesture can also play a role in cognitive growth by providing an imagistic route through which ideas can be made active or brought into the learner's repertoire. The manual modality assumes an imagistic form when it is used in conjunction with a segmented and combinatorial system. Modern-day human communication systems are based on a segmented and combinatorial mode of representation that gives the system its generative capacity. The gestures that speakers produce in the manual modality can express information that they are often not able to express within the codified spoken system. This information is processed by the listener and becomes part of the conversation.