Terrence Deacon


The co-evolution of language and the human brain

Book review by Anthony Campbell. Copyright © Anthony Campbell (1999).

Deacon starts this book by posing a question: why don't animals have language? After all, some of them show good evidence of intelligence in other respects, yet language eludes them. So the book sets out to examine what it is about the human brain that makes it capable of speech.

Deacon approaches the subject from three angles. In Part 1 he considers the nature of symbolic communication; in Part 2 he looks at how the brain is constructed in relation to language, and in Part 3 he sets the discussion in an evolutionary context. As my summary indicates, this is an ambitious book but Deacon is well qualified to write it. He does research in developmental and comparative neurobiology at Harvard Medical School and Boston University, and is also Associate Professor of Biological Anthropology at Boston University. Moreover, he is an excellent writer.

In Part 1 Deacon draws on the work of the American philosopher Charles Sanders Peirce to construct a theory of how human language works (semiotics). This uses three terms: icon, index, and symbol, which are related to one another in a hierarchical manner, and Deacon makes the important and very interesting point that acquiring a grasp of this system, which all human language users must do in order to communicate, requires unlearning as well as learning. In order to shift to a higher level in the hierarchy you have to unlearn the associations you made at the lower level. Deacon uses this idea to explain the astonishing ease with which small children acquire language and also relates it to attempts to teach language to chimpanzees, especially a young bonobo called Kanzi.

It is certainly puzzling that young children have this remarkable ability to learn a complex language, but Deacon does not agree with Noam Chomsky's view that there is an innate Universal Grammar encoded in our brains. He proposes a very interesting alternative idea: namely, that it is language itself which provides this facility. In other words, he suggests that languages "evolve" in order to be easily learnt by young children; those that are easily learned tend to be selected by a sort of evolutionary process. We can think of languages, he suggests, as independent life forms that parasitize human brains. This idea is reminscent of Richard Dawkins's memes, which Deacon mentions in passing.

The icon-index-symbol relationship is not entirely easy to grasp, but it's important for what follows because it underlies the whole of the rest of the book. One intellectual predecessor who I thought might have been mentioned in this context, but wasn't, is the late Gregory Bateson, who put forward a rather similar scheme of logical levels of meaning and who also emphasized the idea that mind is not confined to the body but ramifies out into the symbolic universe around it.

In Part 2 we come to the brain structures which underlie the ability to acquire language; mere increase in brain size, as Deacon demonstrates by a comparative study, is not enough. Specific structures are required to make vocalization possible; Deacon relates the extraordinary story of a harbour seal called Hoover, who acquired—apparently as the result of brain damage caused by infection—the ability to utter speech. But of course, merely being able to form words is not enough either; there must also be structures that allow for symbol formation, and here it is the prefrontal cortex that seems to be important.

Localization of speech function within the brain is discussed in detail in relation to animals and also to humans with various forms of language disorder, congenital and acquired. Certain brain areas (Broca's area and Wernicke's area) are known to be connected with speech, but Deacon doesn't accept that speech is somehow localized in these places; many brain areas are involved in speech. He thinks that these are sites in the brain that act as bottlenecks for information that is passing through the brain as a whole. This explains why damage to these areas disrupts language, but it doesn't mean that language actually resides there.

In Part 3 we look at how the ability to use symbolic communication may have evolved and how this has in turn influenced human evolution. This part of the book is necessarily more speculative than what has gone before. The puzzle is to explain how our apelike ancestors could have developed speech; no living species of ape has this ability apart from us. It's not only the brain that would need to evolve, but also the vocal tract; our larynx has moved to a lower position in our throat compared with other apes, which makes it possible for us to produce more sounds but also makes us liable to choke when swallowing. How far Homo erectus and the Neanderthals were able to speak is uncertain, but Deacon thinks the Neanderthals, at least, were probably able to speak well. He believes that their demise when our own ancestors appeared on the scene was due not to cultural or linguistic inferiority but to diseases brought by the newcomers to which the unfortunate Neanderthals had no inbuilt resistance. This idea is an interesting new speculation but unverifiable, and it suffers from the defect that Neanderthals and modern humans coexisted in some areas for many thousands of years.

Many archaeologists point to the appearance of cave paintings in the Neolithic as evidence of a "great leap forward", and are puzzled by the apparent suddenness with which this occurred; it has even been taken to be evidence of the origin of language. Deacon is rather dismissive of this idea. He suggests that it may have had other causes—perhaps nothing more complicated than increased leisure time thanks to an abundant supply of game. His point is not that this or that cause was definitely responsible for this "advance", but rather that the idea of "advances" itself is a mistake. Many changes that took place, such as the development of agriculture, were probably responses to environmental degradation brought about by human depredation; once made, these changes became irreversible.

In his final chapters Deacon ranges still further afield to consider the implications of his analysis for the angst which, he says, has afflicted modern societies since Descartes. We are increasingly unhappy at the apparent soullessness of the world; there seems to be no place for human values or meaning. This, he holds, is a mistaken view; the universe isn't just mindless clockwork but meaning is intrinsically part of it. He may be right about this, although I think the angst he refers to is more a Western than an Eastern phenomenon; Indian and Chinese thought has historically been less afflicted by the dichotomy.

I found this an immensely stimulating book, in fact one of the most stimulating I've read in years.

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%T The Symbolic Species
%S The co-evolution of language and the human brain
%A Deacon, Terrence
%I Allen Lane (The Penguin Press)
%C London
%D 1997
%G ISBN 0713991887
%P 527 pp
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