The performance of language is multimodal, not confined to speech. Review of monkey and ape communication demonstrates greater flexibility in the use of hands and body than for vocalization. Nonetheless, the gestural repertoire of any group of nonhuman primates is small compared with the vocabulary of any human language and thus, presumably, of the transitional form called protolanguage. We argue that it was the coupling of gestural communication with enhanced capacities for imitation that made possible the emergence of protosign to provide essential scaffolding for protospeech in the evolution of protolanguage. Similarly, we argue against a direct evolutionary path from nonhuman primate vocalization to human speech. The analysis refines aspects of the mirror system hypothesis on the role of the primate brain’s mirror system for manual action in evolution of the human language‐ready brain.

The short answer to the question of How the Brain Got Language is “through biological and cultural evolution.” The challenge is to be more specific. I use the term “the language-ready brain” to suggest that the brain of early Homo sapiens was adequate to support language but that it required tens of millennia for humans to be able to exploit these innate neural capabilities to develop, cumulatively, languages and the societies that made languages possible and necessary. The ability to surf the World Wide Web is a recent example of society's expanding ability to develop technologies and social structures which allow humans to exploit their neural capabilities in ways that were not part of the adaptive pressures for biological evolution.The two-fold challenge of the book, then, is to understand (i) what are the mechanisms of the language-ready brain and what adaptive pressures evolved them biologically; and (ii) how did those mechanisms support the emergence of language as well as modern-day patterns of language change, acquisition and use, and the social interactions which support them?

The paper introduces dyadic brain modelling, offering both a framework for modelling the brains of interacting agents and a general framework for simulating and visualizing the interactions generated when the brains (and the two bodies) are each coded up in computational detail. It models selected neural mechanisms in ape brains supportive of social interactions, including putative mirror neuron systems inspired by macaque neurophysiology but augmented by increased access to proprioceptive state. Simulation results for a reduced version of the model show ritualized gesture emerging from interactions between a simulated child and mother ape.