Language Evolution and Computation Bibliography

Language existed before human populations became separated (all descendant populations have language) but language did not emerge until long after these population divergences occurred (behavioral modernity only showed then). Distinguishing capacity for language from externalized language resolves the apparent paradox, eliminates the need of proto-language, and rules out monogenesis. Speech emerged only after the capacity for language became (sufficiently) fixated in the species. This accords well with a fundamental property of human language. Rules mapping to meaning rely on structural properties only, while rules mapping to sound are (also) sensitive to linear order, reflecting properties of sensorimotor modalities. The asymmetry suggests (i) primacy of internal language over speech/sign, and (ii) evolution of capacity of language preceding externalized language. Click phonemes with their unique geneological, genetic and geographical distribution may be relevant here. All biologically Khoisan groups speak click languages, which are spoken by biologically Khoisan groups only. Separation followed possession of internal language but preceded externalized language. Clicks were recruited for externalization in San populations only after deepest separation.

Can a child who is not exposed to a model for language nevertheless construct a communication system characterized by combinatorial structure? We know that deaf children whose hearing losses prevent them from acquiring spoken language, and whose hearing parents have not exposed them to sign language, use gestures, called homesigns, to communicate. In this study, we call upon a new formal analysis that characterizes the statistical profile of grammatical rules and, when applied to child language data, finds that young children's language is consistent with a productive grammar rather than rote memorization of specific word combinations in caregiver speech. We apply this formal analysis to homesign, and find that homesign can also be characterized as having productive grammar. Our findings thus provide evidence that a child can create a combinatorial linguistic system without external linguistic input, and offer unique insight into how the capacity of language evolved as part of human biology.