Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.
This primary or social interaction seems to derive directly from an older system and, like all animal systems of communication, is restricted to between you and me, here and now. The secondary communication interaction, speech, is subjects to no such limitations in space and time. ... Though sign languages are onomatopoetic, the signs represent quite arbitrary features of any referent; each Australian sign language, for example, uses quite different signs for familiar animals. Aborigines find signing faster than speaking and more effective at distances, and some groups consider it more elegant than speech. A deaf Aboriginal grows up with access to every aspect of his culture, and joins freely in any conversation. The human facility for mime and its appreciation and our ready grasp of the symbolism in dance, myth, dreams, and art require some explanation. A similar talent is seen in the emergence of natural sign language in every institution for the care of deaf children. These talents would be explicable if speech had evolved through long periods of mime and signing. Natural sign languages are found among the Plains Indians, among all Australian Aborigines, in India, and in many regions around the Mediterranean. They seem to have been studied seriously by only one man, La Mont West, whose conclusions have never been published. He is known to have believed that all of the sign languages had the same syntactic form. If this is so, then it becomes a reasonable evolutionary hypothesis that the deep structure of modern languages is closely related to that of natural sign languages. Perhaps this hypothesis could provide a test of speculations on the evolution of human language. (McBride, G (1973) Comments on ... Primate communication and the gestural origins of language. Current Anthropology 14: 15)