As part of the continuing growth and diver sification of Language and Cognition, this special double issue focuses on the evolution of language. Although this controver sial topic has been discussed for centuries from different per spectives, it is probably safe to say that genuine progress has only begun to take place during the past 25 years or so, as increasing numbers of researcher s have star ted pooling a broad array of relevant ideas and discoveries from a tremendous range of disciplines, including, in alphabetical order, anthropology, archeology, ar tificial life, biology, cognitive science, genetics, linguistics, modeling, neuroscience, paleontology, primatology, and psychology. The rapid expansion and maturation of this field of inquiry is evident in sever al ways. Since 1990, more and more articles about the evolution of language have appeared in prominent, high-ranking journals such as Behavioral and Brain Sciences, Trends in Cognitive Sciences, Proceedings of the National Academy of Science, and Frontiers in Evolutionary Neuroscience. In addition, the publication of books on this topic has been on the rise, and there is now a whole series of impressive monogr aphs under the rubric “Oxford Studies in the Evolution of Language.” Fur thermore, beginning in 1996, the International Conference on the Evolution of Language has been held every other year to provide a public forum for the presentation and evaluation of new developments (http://www.evolang.org/).

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?

Arbib offers a coherent proposal of how the brain has evolved to become language-capable. Integral to the argument are mirror neurons, cells discovered in macaque brains with interesting firing patterns, and studies on gestural communication of great apes. Here, I first discuss some complexities of the recent mirror neuron literature, which suggest that ‘mirroring’ may be an ontogenetically acquired, not an evolved, feature of neurons. Second, it is now clear that chimpanzee vocal behaviour is strongly mediated by social variables, and that individuals can use vocalisations to persuade and inform others, facts that have implications for gestural theories of language evolution. I conclude with discussing research most needed for making progress in understanding how human language has evolved.

In this book it has been proposed that the mirror system can be a scaffold for building a language-ready brain, because of its property of matching action observation with action execution, a feature that can correspond to the “parity” requirement for communication. In this commentary we will first emphasize two properties of mirror neurons and motor cortex that may have contributed to language: the generalization of the property of understanding action goals and the capacity to decode the goal of action sequences. Then we will propose, based on recent behavioural and neurophysiological data in monkeys, that the vocalization in non-human primates could have reached a partial voluntary control, thus contributing to the emergence of a communicative system relying on the coordination of gestures and utterances.

The Mirror System Hypothesis of Michael Arbib (2012), with respect to the cultural evolutionary origins of syntactic structure, allows to make a set of predictions about the neural mechanisms that govern the processing of modern human languages. Neuroimaging techniques may be employed to test these predictions and inform an evolutionary theory of language syntax. In this commentary, I will argue that future neuroimaging research needs in particular to: i) clarify whether linear sequential versus non-linear hierarchical structure differentially depend on mirror neurons as opposed to higher-order heteromodal cortices; ii) challenge current neuroscientific evidence on multilingualism: as it stands, syntactic processing appears to be mediated by the same neural mechanisms across languages, independently of cross-linguistic idiosyncrasies; iii) devise longitudinal studies of grammar acquisition in newborns and children; iv) recreate in the laboratory nearly-ecological conditions for the emergence of syntactic constructions through cultural and social interaction, and exploit the “experiment of nature” of pidgin and creole languages.

In this commentary, I argue (i) that there are some peripheral homologies between the monkey and the human vocalization systems; (ii) that complex vocal learning can be achieved without need of a voluntary hand grasping circuit; and (iii) that in the monkey there are rudimentary circuits that can convey auditory information into Broca's region, via the “ventral pathway” but also via the arcuate or the superior longitudinal fasciculi.

Arbib's How the brain got language is a major achievement in defining a trajectory for the evolution of complex imitation and the language-ready brain leading to human language. In addition to these capabilities, I will suggest that it is useful to consider two additional components of human brain function that are intricately related to the emergence of language. These are, first, the profound human motivation to represent and share the psychological states of others, and second, the related complex semantic system that represents the contents of what is communicated in language. In this sense, these two components represent part of what is under the iceberg, where language is the emerging tip.

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.