Michael Corballis is a psychologist with a strong interest in lateralization, handedness, and the origins of language. In this book, he puts these interests together with a solid and comprehensive survey of other background material relevant to the origins of language. The book also pushes Corballis' own specific hypothesis, that human languages were implemented mainly in manual gestures until about 50,000 years ago, at which point largely vocal language took over as an invented cultural innovation. This is an argument about the medium in which linguistic messages were expressed. Corballis believes that the human capacity for generative syntactic language may possibly be as old as one million years. The argument is much less about when true linguistic generativity arose than about the hypothesized relatively recent switch to the vocal medium.
While conceding that Corballis succeeds in showing that this late switch to vocal language was possible, it still seems to me to be very unlikely. Corballis claims that the hominins of 150,000 years ago communicated mainly by manual gestures, but were (and here he agrees with the dominant view) biologically essentially the same as modern humans. Thus, they would have had all the potential of modern babies for acquiring skilled vocal articulation and control of complex phonological systems. Vocal language comes very naturally to modern humans. What took our ancestors so long (about 100,000 years!) to `discover' the advantages of vocal language? Corballis believes that vocal language does have advantages over manual language, and this, he argues, accounts for the displacement of the earlier waves of Homo sapiens by later waves of the same species, technologically superior due to possession of the better medium for language. Corballis' argument is a revamping of a position that used to be common among archeologists, especially those concentrating on the European Upper Paleolithic, that truly generative language itself did not emerge until some 45,000 years ago. At least he does not repeat that implausible suggestion. Instead, he has pushed the beginning of generative language back to around the beginning of Homo sapiens, which does seem plausible, while idiosyncratically sticking with a much later switch into the modern preferred vocal medium.
The argument for successive waves of Homo sapiens displacing each other is backed by DNA dating evidence, from which Corballis strategically chooses to rely on the shortest estimates of time back to the common ancestor of all non-African humans, about 50,000 years. But this argument conveniently forgets the African members of the human race; the common ancestor of all humans probably lived at least 150,000 years ago. The story outside Africa was apparently that the technologically superior humans with vocal language displaced their still manually communicating cousins from the gene pool, while back in Africa what must have happened was that the manually communicating people had the good sense to adopt the ways of the vocalists without getting outbred by them. Corballis does not pursue this African/non-African difference, though it seems to me to be pretty important for his case.
Most linguists will be dismayed to see that Corballis has swallowed the arguments of the long-range reconstructors such as Merritt Ruhlen. Clearly the idea that some pan-human etymologies can be reconstructed fits in quite well with the claim for a wave of newly-vocal humans conquering the world starting about 50,000 years ago. But here Corballis should have checked with a few more linguists. Most opponents of long-range reconstruction do believe that there may have been one single (spoken) human language, to which all modern languages could in principle trace some of their roots. The problem is that too much time has elapsed since this putative mother of all languages existed, and the routes to the present are in all likelihood totally obscured by later changes. As linguists like Larry Trask, Don Ringe and Lyle Campbell, to name but a few, loudly insist, no good answer has yet been given to the charge that the correspondences noted by the long-range reconstructionists are not above the chance level. In other words, no effort has been put into rejecting the null hypothesis. One might have expected a psychologist, above all, to be sensitive to this statistical problem.
Oddly perhaps, although the book's central argumentative thesis is, I believe, badly flawed, I still found this a very useful book in many ways. It does a good job of summarizing the tangled material on the prehistory of our species from Australopithecus onward, with a lot of very recent research mentioned. And on the complex situation regarding lateralization and handedness Corballis is in his own element and a leading authority. As an indication of how fast research in this area is moving, Enard et al (2002) have now discovered that a gene (FOXP2) which appears to be involved in articulation, probably underwent a mutation within the last 100,000 years. Hence the final step in the emergence of a fully vocal language may have been due to a mutation, not to a cultural innovation. Corballis, of course, could not have known of this while writing his book. I believe most scholars of the origins of language will now be convinced that manual gestures played an important role in bootstrapping humans into communication systems capable of referring and of describing, at first iconically, a range of different actions. I will warmly recommend this book to my students in a course on the origins and evolution of language, but with the health warnings mentioned above.
The book is excellently written and structured. It is characterized by a lot of wry humour, some of which had me spontaneously laughing aloud. Read it -- it's fun; the factual summaries, apart from the misadventure into Ruhlen-land, are useful, and the problematic central argument is, one feels, by no means the whole point of the book. I also liked the novel layout adopted by Princeton University Press, where the footnotes occupy a narrow small-print column down the outside of the page.