Human Language and Our Reptilian Brain: The Subcortical Bases of Speech, Syntax, and Thought (review)

In his latest book, Philip Lieberman argues for the existence of what he calls the functional language system. Language is a complex biological adaptation, he argues, and like all complex biological adaptations involving behavior it rests on a combination of evolutionarily old neural circuitry, the use of old neural circuitry for new functions, and some new neural circuitry as well. As indicated by the title, Human language and our reptilian brain, he is especially eager to point out the contributions of very old parts of the human brain. Perhaps the main idea is best conveyed by his claim that ‘Ultimately, human linguistic and cognitive ability can be traced back to the learned motor responses of mollusks’ (2).

The theoretical thrust of the book is against modularity and innate linguistic knowledge as espoused by Noam Chomsky and others. L relates the rationale for modular construction in various kinds of modern technologies and then argues, briefly and persuasively, that the empirical facts are that the human brain does not work in this way: ‘Biological brains simply do not conform to the design principles of radar sets or conventional digital computers’ (11). From a similarly brief and persuasive review of the neurophysiological evidence, he claims that ‘These biological facts all argue against neural structures that code innate linguistic knowledge’ (5; see also Elman et al. 1996). He also points out that the notion of linguistic competence, as divorced from performance, is not really biologically plausible, as natural selection can work only on outwardly expressed behaviors. There is no question that language is unique to the human species, but in L’s view it is best understood as a new and unique combination of old things, the vast majority of which we share with other animal species.

The book is actually meant for a fairly wide popular audience. We thus get in Ch. 1 an elementary tour of the brain and a brief primer on connectionist networks, and in Ch. 2 we are given a lesson on how humans produce and perceive the sounds of language physically. We also learn quite a bit along the way about various kinds of brain damage and other abnormalities and their effects on human linguistic abilities. Ch. 3 reviews, textbook style, selected studies on verbal working memory and its neurophysiological bases.

Chs. 4–6 are updates and refinements of the thesis put forth originally in Lieberman 1985 to the effect that the neural mechanisms underlying human linguistic (especially syntactic) abilities evolved from ones originally adapted for the planning and sequencing of concrete motor actions. Specifically, the proposal is that a key aspect of human syntactic ability resides in the subcortical basal ganglia, which seem to be mainly responsible for sequencing motor activity: ‘In a sense, human language and thought can be regarded as neurally “computed” motor activity’ (158). He also makes it very clear in these chapters that he has never held the view that only modern humans, in the last 150,000 years, have had language. He has sometimes been caricatured as holding this view because he has been arguing for some time that earlier hominids could not produce the full range of speech sounds that characterize modern human language. But the claim is simply that the anatomical changes in the human supralaryngeal vocal tract that occurred with modern humans enabled the more efficient production and comprehension of speech—clearly implying that some forms of language and speech were already present with premodern humans. He even goes to some pains to argue that language-trained apes such as Kanzi acquire from their unique environments language skills that differ from human skills only quantitatively, not qualitatively. L’s evolutionary story is self-consciously Darwinian and gradualist.

The book makes good evolutionary arguments about how human beings came to have at least some of their linguistic abilities, especially those involving speech. In fact, exciting data...