Language Evolution and Computation Bibliography

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.

The mirror system provided a natural platform for the subsequent evolution of language. In nonhuman primates, the system provides for the understanding of biological action, and possibly for imitation, both prerequisites for language. I argue that language evolved from manual gestures, initially as a system of pantomime, but with gestures gradually `conventionalizing' to assume more symbolic form. The evolution of episodic memory and mental time travel, probably beginning with the genus Homo during the Pleistocene, created pressure for the system to `grammaticalize,' involving the increased vocabulary necessary to refer to episodes separated in time and place from the present, constructions such as tense to refer to time itself, and the generativity to construct future (and fictional) episodes. In parallel with grammaticalization, the language medium gradually incorporated facial and then vocal elements, culminating in autonomous speech (albeit accompanied still by manual gesture) in our own species, Homo sapiens.

Recognising that signed languages are true languages adds to the variety of forms that languages can take. Such recognition also allows one to differentiate those aspects of language that depend on the medium (voiced or signed) from those that depend on more cognitive aspects. At least some aspects of language, such as symbolic representation, time markers, and generativity, may derive from the communication of the products of mental time travel, and from the sharing of remembered past and planned future episodes.

One of the properties that most conspicuously distinguishes human language from any other form of animal communication is generativity. Language with this property therefore presumably evolved with the Homo line somewhere between H. habilis and H. sapiens sapiens. Some have suggested that it emerged relatively suddenly and completely with H. sapiens sapiens, and this view is consistent with (a) linguistic estimates as to when vocal language emerged, (b) the relatively late 'explosion' of manufacture and cultural artifacts such as body ornamentation and cave drawings, and (c) evidence on changes in the vocal apparatus. However, evidence on brain size and developmental patterns of growth suggests an earlier origin and a more continuous evolution. I propose that these scenarios can be reconciled if it is supposed that generative language evolved, perhaps from H. habilis on, as a system of manual gestures, but switched to a predominantly vocal system with H. sapiens sapiens. The subsequent 'cultural explosion' can then be attributed to the freeing of the hands from primary involvement in language, so that they could be exploited, along with generativity, for manufacture, art, and other activities.