Michael Arbib's book proposes a scenario of language evolution that begins with pantomime, progresses to proto-sign, and then develops together with proto-speech in an “expanding spiral” to create a language-ready brain. The richness of detail in Arbib's hypothesis makes serious appraisal of each of its aspects possible. Here I describe findings about established and emerging sign languages that bear specifically upon the interaction between sign and speech proposed in the Mirror System Hypothesis. While supporting the central role that Arbib attributes to gestural/visual communication in understanding language and its evolution, I point out some kinks in the spiral that potentially disrupt its smooth expansion. One is the fact that each modality relies on an entirely different motor system. Another is the type of relation that holds between the articulators and grammatical structure, which is radically different in each system as well. A third kink disrupts the proposed continuity between holistic pantomime (gestural holophrases) and signs. Given such differences, instead of a scenario in which speech grew out of sign, it seems more likely that the two modalities complemented each other symbiotically throughout evolution as they do today. If so, then the modern ability to spontaneously create sign languages reveals the extraordinary richness and plasticity of human cognition, and not an evolutionary stepping stone to speech.

I suggest two puzzles for the Mirror System Hypothesis. First, there is little evidence that mirror neuron populations for words or for signs exist in Broca's area, and a mirror system is not critical for either speech or sign perception. Damage to Broca's area (or to the mirror system for human action) does not result in deficits in sign or speech perception. Second, the gesticulations of speakers are highly integrated with speech, but pantomimes and modern protosigns (conventional gestures) are not co-expressive with speech, and they do not co-occur with speech. Further, signers also produce global, imagistic gesticulations with their mouths and bodies simultaneously while signing with their hands. The expanding spiral of protosign and protospeech does not predict the integrated and co-expressive nature of modern gestures produced by signers and speakers.

In this article, I will comment on recent advances in the research on the intersection between language and action. On the basis of the argument proposed by Arbib, I will consider an evolutionary scenario according to which language emerged from a basic imitation mechanism devoted to action representation. I will review more appropriate data in patients who present with gesture and language disorders and add it to behavioral, neurophysiological, and neuroimaging evidence that suggests that specialized sensorimotor circuits underlie action processing and may ultimately even ground complex aspects of language. Finally, in the last part of the article, I will discuss some of the future research on the interwoven processes of production and comprehension that are involved in the predictive mechanisms of action and language.

Motor theories of perception posit that motor information is necessary for successful recognition of actions. Perhaps the most well known of this class of proposals is the motor theory of speech perception, which argues that speech recognition is fundamentally a process of identifying the articulatory gestures (i.e. motor representations) that were used to produce the speech signal. Here we review neuropsychological evidence from patients with damage to the motor system, in the context of motor theories of perception applied to both manual actions and speech. Motor theories of perception predict that patients with motor impairments will have impairments for action recognition. Contrary to that prediction, the available neuropsychological evidence indicates that recognition can be spared despite profound impairments to production. These data falsify strong forms of the motor theory of perception, and frame new questions about the dynamical interactions that govern how information is exchanged between input and output systems.

This paper considers Arbib's hypothesis that (oral) language has its roots in gesture in light of recent research on demonstratives, joint attention, and deictic pointing (Michael Arbib. 2012. How the brain got language: The Mirror System Hypothesis. Oxford: Oxford University Press). It is argued that demonstratives provide an important link between gesture, discourse, and grammar that rests on their communicative function to coordinate the interlocutors' focus of attention. Combining evidence from linguistic typology and historical linguistics with evidence from research on social cognition, the paper argues that demonstratives constitute a universal class of linguistic expressions that are commonly used in combination with a deictic pointing gesture to establish joint attention, a cognitive phenomenon that is closely related to Arbib's notion of “complex imitation”. No other class of linguistic expressions is so closely tied to the speaker's body and gesture than demonstratives. However, demonstratives are not only used to focus the language users' attention on concrete entities in the surrounding situation, they are also used to organize the information flow in discourse, which in turn underlies their frequent development into a wide range of grammatical markers, e.g. definite articles, third person pronouns, relative markers, complementizers, subordinate conjunctions, copulas, and focus markers. In this way, demonstratives provide an explicit link between gesture, imitation, and grammar that is consistent with Arbib's theory of the evolution of language.

In this book, Michael Arbib presents a most interesting and comprehensive account of the evolution of language. The work is both impressive and convincing in its description of how the language-ready brain evolved and how languages emerged through cultural evolution. As we are in broad agreement with Arbib's evolutionary story at the neurocognitive level, we focus on an underdeveloped part of his argument: when did language evolve in the human lineage? How does Arbib's neurocognitive argument connect with what archeology teaches us about human evolution?

Arbib hypothesizes that evolutionary modern language significantly postdates human speciation. Why should this be so? I propose an account based on niche construction theory, in which Arbib's language-ready brain is primarily a consequence of epigenetically-driven adaptation to the biocultural niche of protolanguage and (subsequently) early language. The evolutionary adaptations grounding language evolution were initially to proto-linguistic socio-communicative and symbolic processes, later capturing and re-canalizing behavioural adaptations (such as serial and hierarchical constructive praxis) initially “targeted” to other developmental and cognitive domains. The intimate link between praxic action and symbolic action is present not only in the human brain, but also in the human biocultural complex. The confluence of praxis and symbolization has, in the time scale of sociogenesis, potentiated the invention of domain-constituting and cognition-altering symbolic cognitive artefacts that continue to transform human socio-cultural ecologies. I cite in support of this account, which differs only in some emphases from Arbib's account, my colleagues' and my research on cultural and linguistic conceptions of time in an indigenous Amazonian community.

The present article responds to commentaries from experts in anthropology, apraxia, archeology, linguistics, neuroanatomy, neuroimaging, neurophysiology, neuropsychology, primatology, sign language emergence and sign language neurolinguistics on the book How the brain got language: The mirror system hypothesis (Arbib 2012). The role of complex imitation is discussed, and the distinction between protolanguage and language is emphasized. Issues debated include the role of protosign in scaffolding protospeech, the interplay between biological evolution of the brain and cultural evolution of the social interactions within groups, the relations brain mechanisms for action and language, and the question of when language first emerged.