What are the neurological bases of human language, and how did they evolve? What makes human language special? For the past two hundred years virtually all attempts to account for the neural bases and evolution of language have looked to the neocortex, the most recent evolutionary aspect of the mammalian brain. In recent years, following Noam Chomsky's lead, linguistic research has virtually equated syntax with language. Syntactic ability is taken to be a unique characteristic of the human mind, deriving from genetically transmitted "language instinct."
In this provocative book, Lieberman shifts the focus, arguing that language is not an instinct coded in a discrete cortical "language organ", but a learned skill, based on a Functional Language System distributed over many parts of the human brain. To make his case, Lieberman synthesises converging behavioral and neurobiological data, including clinical evidence from speech-impaired patients (some with Parkinson's disease, whose deficits are subcortical, and some with Broca's aphasia); neuroimaging; and evolutionary biology. Using this enormous body of data, he argues that human language is regulated by a network that involves regions of the neocortex often associated with nonlinguistic cognition, and even subcortical structures-our ancient reptilian brain-in addition to Broca's and Wernickes areas in the neocortex.
In this challenging view, our language capacity is overlaid on sensorimotor systems that originally evolved to do other things than support language, and that continue to do them now-namely, yield timely motor responses to environmental challenges and opportunities. In Lieberman's view, the FLS is dynamic and adaptive, responding to situational requirements. It rapidly integrates sensory information with stored knowledge and enlists additional neural resources, such as the regions of the frontal lobes, in response to task difficulty.
In a further development of his evolutionary argument, Lieberman goes on to maintain that although the neural substrate that allows us to acquire language is innate, nothing about particular languages, including their grammar and syntax, is innate. Nor are the mental operations carried out in our brains compartmentalised in the modular manner proposed by many linguists and cognitive scientists (he points out that functional neuroimaging shows no neat matches between linguistic theory and current neuroscientific knowledge about linguistic functioning). lnstead, the neural bases of human language are intertwined with other aspects of cognition, motor control, and emotion.
Ultimately, then, Lieberman concludes, the human FLS is unique, but its anatomy and physiology derive from neural structures and systems that regulate adaptive behavior in other animals. This exciting hypothesis, deeply informed by evolutionary theory and evolutionary biology as well as by current research in neuroscience and neuropathology, offers a sharp Darwinian challenge to much current thinking in linguistics and cognitive science, and will provoke new research and debate for years to come.