Language as gesture.

Language can be understood as an embodied system, expressible as gestures. Perception of these gestures depends on the "mirror system," first discovered in monkeys, in which the same neural elements respond both when the animal makes a movement and when it perceives the same movement made by others. This system allows gestures to be understood in terms of how they are produced, as in the so-called motor theory of speech perception. I argue that human speech evolved from manual gestures, with vocal gestures being gradually incorporated into the mirror system in the course of hominin evolution. Speech may have become the dominant mode only with the emergence of Homo sapiens some 170,100 years ago, although language as a relatively complex syntactic system probably emerged over the past 2 million years, initially as a predominantly manual system. Despite the present-day dominance of speech, manual gestures accompany speech, and visuomanual forms of language persist in signed languages of the deaf, in handwriting, and even in such forms as texting.