In From Hand to Mouth: The Origins of Language Michael Corballis provides an engaging, highly readable and provocative account of the evolution of human language. The primary thesis of his book is that language evolved from manual and facial gestures rather than from animal vocalizations, as is often assumed. While this point of view has been expressed by others during the last few centuries (for example, Condillac in 1747), it has never been argued more forcefully and with as much supporting scholarly evidence. (I suspect that it has also never been argued with greater use of hand/mouth adages, clichés and puns.) Among the more provocative ideas is the suggestion that human speech, like writing, was a cultural invention subsequent to gestural language rather than the evolutionary essence of language.

In developing his case, Corballis places a good deal of emphasis on the fact that neuroscientists have discovered individual neurons in the frontal lobe of monkey brains that respond to particular reaching and grasping movements made by the animal and that also respond when the monkey observes the same movements being made by other monkeys or humans. These mirror neurons provide a clear link between gesture production and gesture perception. It is interesting that the mirror neurons in monkeys have been found in an area that corresponds to an area of the human brain that is involved in the production of speech (Broca's area) and that there is evidence of a similar mirror-neuron system in present day humans as well. Because the mirror-neuron system is found in both present-day monkeys and present-day humans, Corballis argues that it is likely that such a system for linking action and perception for gesture was present in the last common ancestor before the split of monkeys and apes, perhaps as much as 30 million years ago. The early evolutionary appearance of the mirror-neuron system for gesture is likely to have been an important step in setting the stage for the eventual emergence of gestural communication.

Though it is impossible to do justice to Corballis' book in a brief review, his evolutionary scenario goes something like this. About 16 million years ago, the great apes (which eventually led to our species) split off from monkeys. Corballis argues that the evolution of larger brains in the line that eventually led to humans enabled an increase in the kind of “offline” thinking that could set the cognitive stage for the emergence of “protolanguage,” the kind of gestural communication that can be acquired by present-day apes. About 5 or 6 million years ago, bipedalism emerged and distinguished hominins from the other great apes. Walking upright freed the arms and hands for even more effective gesturing and for actions that were voluntary and preplanned rather than reflexive. Against this backdrop, the genus Homo emerged about 2 million years ago, accompanied by still larger brains, by the invention of stone tools, and by multiple migrations out of Africa. Corballis suggests that gestural language became more sophisticated during this time period, perhaps driven by emergence of the cognitive ability to imagine novel scenes and to think recursively (as, for example, in, “I know that you know that I know that you see me”). Emergence of recursive thought and of the ability to think of things that are novel or not present permits the emergence of grammar, generativity and other characteristics that distinguish language from protolanguage.

On Corballis' view, language during this period was primarily gestural, though it was likely punctuated by vocalizations consisting of grunts, groans, cries and the like. In fact, changes in the vocal tract that permitted the kind of enhanced cortical control of vocalization and breathing that we see in present-day humans may not have been complete until our species, Homo sapiens, emerged approximately 150,000 years ago. Moreover, such adaptations may have been favored specifically because they augmented an already existing gestural language.

If gestural language emerged first and was so powerful, then why did vocal language emerge at all? As Corballis argues, it is relatively easy to see the advantage of a language system that could be used in the dark or when individuals were out of sight from each other and that could permit communication even while the hands were being used for other things such as demonstrating how to make or use a particular tool. In fact, the transition from primarily gestural to primarily vocal language may have coincided with an explosion of art, culture, and technology that occurred in Europe approximately 40,000 years ago.

I suspect that most readers of this book will, like me, have an easier time accepting the premise that gestural communication was an important development on the way to vocal language than they will have accepting the more provocative suggestion that vocal language was a cultural invention. In Corballis' own words, “My guess is that our own species, Homo sapiens, discovered [emphasis added] that language could be conveyed more or less autonomously by speech alone…. The invention [emphasis added] of autonomous speech may have been as recent as 50,000 years ago.” (p. 218) On this view, rather than being a biological imperative or being the initial or essential form of language, speech becomes very much like writing, mathematics and other cultural inventions that facilitate and enhance communication.

As Corballis develops this evolutionary scenario over the ten chapters of his book, he provides insightful analysis of several related topics. This includes a very useful discussion of the nature of language and of the characteristics that distinguish a “true” language from protolanguage and other forms of communication. It also includes consideration of factors leading to the emergence of such evolutionary landmarks as bipedalism and of the emergence of handedness and hemispheric asymmetry. With respect to the topic of functional hemispheric asymmetry, Corballis builds on the account provided in his earlier books, especially The Lopsided Ape (1992).

Of particular importance to his discussion of hemispheric asymmetry are Corballis' speculations regarding the emergence of left-hemisphere dominance for language in general and for speech in particular. As he notes, there is evidence of left-hemisphere superiority for vocalization in several present-day species, including some species of frogs, with which we shared the last common ancestor approximately 170 million years ago. Though vocalizations in other species do not constitute language, the ubiquity of left-hemisphere dominance suggests that cerebral asymmetry for vocalization may be quite old in evolutionary terms. If this is the case, then it should come as no surprise that when vocal language did eventually develop in humans it would be associated with the already existing left-hemisphere superiority for vocalization. And, it is certainly plausible to suppose that any left-hemisphere dominance for fine motor movements or for gestural language would have been reinforced as language was extended from gesture to vocalization.

Testing evolutionary scenarios is always tricky because it is not possible to simply go into a laboratory and conduct the relevant set of experiments. In building his case, Corballis reviews circumstantial evidence from an extraordinarily wide range of fields and he does so with both scholarship and wit—not an easy combination to pull off. The technique of looking for similarities among contemporary species and then supposing that those similar characteristics were present in their last common ancestor has been used very effectively. Corballis also provides a very effective analysis of gestural communication in present-day humans. To the extent that language emerged first in the form of gesture, we should be able to find evidence for true gestural language in present-day members of our species. In building his case, Corballis makes very good use of contemporary research on signed language systems in humans, though it must be noted that there is far from unanimous agreement about whether these systems constitute formal language.

In short, this is an important book on an important topic. Though not every reader may agree with every conclusion, Corballis lays out his evidence and his logic with sufficient clarity that critics will know exactly what they have to deal with. From Hand to Mouth should be studied by everyone with a serious interest in the origins of language and read by others who want an evolutionary account that is as entertaining as it is informative.