American Scientist

The Dawn of Human Culture. Richard G. Klein with Blake Edgar. 288 pp. John Wiley & Sons. $27.95.

Human evolution is not a neglected topic: A search on amazon.com, for example, turns up more than 1,400 books on the subject. Stanford anthropologist Richard Klein has written several, including the widely acclaimed The Human Career, and science writer Blake Edgar has collaborated with Donald Johanson on two. True, knowledge of our ancestry is growing fast, so there are always new additions to the old story. But more than that is needed to justify yet another overview of how we became us.

The new book Klein has written with Edgar, The Dawn of Human Culture, aims to bring the very latest developments in paleoanthropology to a wide, nonspecialist audience. Clear, readable and briskly written, it covers six million years in under 300 pages and includes plentiful maps, diagrams and illustrations. Although it contains little that is new to those familiar with the field, it provides newcomers with an introduction that is more than adequate in some respects, if slightly less so in others.

I'm not just trying to be funny in describing this as a bare-bones account of human evolution: It concentrates heavily on the fossil and archaeological records, with relatively little coverage of what we can deduce about human behavior from those and other sources (paleoclimatology, comparative primate studies and so on). True, such deductions must always contain elements of conjecture. But according to the authors themselves, "paleoanthropologists know that their first priority must be to understand how ancient people looked and behaved" (italics added). After plowing through lengthy discussions of skeletal differences between Homo habilis, Homo rudolfensis and Homo ergaster, and the tools that each produced, readers might thus reasonably expect to find at least a little about how members of those species subsisted; how their lives were organized; what climates, terrains and ecologies they shared; their relations with the large and efficient predators that ranged their habitat; and much more. Instead, the book takes us off to Java on the wave of post-ergaster expansion, then back to more stones and bones.

Maybe it's this emphasis on skulls, rather than on what these skulls contained, that leads Klein and Edgar to a somewhat naive view of the relationship between brain size and intelligence. Throughout, they assume that larger brains automatically yield higher intelligence. They do not appear even to notice the seemingly insoluble paradox that results from this assumption.

Throughout most of human evolution, brains grew to triple the size of ape brains, while toolkits remained crude, meager and almost unchanging over periods of hundreds of thousands of years. If our ancestors were getting smarter, they certainly weren't showing it. But when human culture finally did explode, this was preceded not by an increase but by a small decrease in average brain size!

Klein and Edgar are well aware of these facts, which no paleoanthropologist disputes. They agree that the artifacts of Homo erectus "appear to have remained remarkably stable for a million years or more." They admit that Neandertals "produced a very small range of readily distinguishable stone tool types" and "rarely if ever crafted artifacts from plastic substances like bone, ivory, shell, or antler." And even when it comes to our own species, they tell us, "Africans and Europeans remained behaviorally similar?and still primitive?until about 50,000 years ago."

Yet Klein and Edgar continue to insist that our ancestors were really getting more intelligent. They cite, for instance, UCLA neuroscientist Harry Jerison's proposal that a spurt in brain growth about 600,000 years ago conferred "the ability to accumulate novel behaviors, such as those we detect through time in the archaeological record" and his conclusion that "'selection for brain size must have been selection for increased or improved information-processing capacity.'" Among Neandertals, too, "a larger brain promoted new, highly adaptive behaviors, including an unsurpassed ability to flake stone." Once again, no other "novel behavior" is actually mentioned.

Even the sole evidence Klein and Edgar offer for this alleged enhancement of intelligence?the improvement of stone tools?is thin. Although they spend a whole page speculating on exactly what Acheulean hand axes were used for, they fail to address Iain Davidson's claim that hand axes weren't tools at all, but were simply the discarded cores of stones from which sharp-edged flakes had been struck. (In the illustration on the next page, compare the bottom left-hand object in the the top panel?characterized as an Oldowan core?with the top left-hand object in the bottom panel?described as an Early Acheulean hand axe. They are virtually identical.) If Davidson is right, the famed "improvement" in hand axes 600,000 years ago would simply mean that knappers were getting more and finer flakes from each stone. This would make yet more mysterious the mystery of how human culture flowered so abruptly.

In the book's brief final chapter, Klein and Edgar claim that the cultural explosion of 50,000 years ago was most likely triggered by the emergence of modern human language, and that language in turn arose through some kind of mutation affecting the way the human brain was organized. This is the "bold new theory on what sparked the 'big bang' of human consciousness" promised to readers so prominently on the dust jacket.

Is this theory truly new? Well, no. I, for one, wrote about it 12 years ago. Is it truly bold? "Rash" might be a better description, if the original reactions of biologists and neurologists are any guide. It is, indeed, highly implausible that a mutation could have such far-reaching consequences; any rewiring of the brain required for language would be far too complex and extensive. The sole supporting evidence the authors adduce is an article on "specific language impairment" (a still somewhat controversial condition that may affect nonlinguistic behaviors too) by geneticist Cecilia S. L. Lai and colleagues in the October 4, 2001, issue of Nature. Klein and Edgar interpret this research as indicating "that a single mutation could underlie the fully modern capacity for speech," although it suggests no such thing. The condition itself may indeed result from a single defective gene, but that doesn't mean the undamaged gene is the cause of language. That would be like saying that the broken plug on your television set was what had previously brought you the picture.

To read Klein and Edgar's account, you might suppose they were the first people to think about the evolution of language and its possible effects on human culture. In fact, over the past dozen or so years, countless books and articles on this topic have appeared, not one of which do they cite. Although they are probably right in concluding that language did indeed bring about a cultural explosion, their timing is almost certainly off. They subscribe to the Fallacy of Instant Consequences, assuming that language must have triggered modern human behavior the moment it appeared.

But language doesn't enforce creativity?it merely makes it possible. Truly creative individuals are rare, even in our species, so the human population, probably tiny to begin with, had to achieve a critical mass before anything new could show up in the archaeological record. Moreover, according to some experts, all the phenomena that came together in Europe 40,000 or 50,000 years ago had already appeared, singly and at scattered sites, in Africa over the previous 50,000 years. Thus the likeliest conclusion is that language as we know it arose, most probably through some fusion of preexisting capacities, around the time our species originated?more than 100,000 years ago.

Precisely how this happened remains one of the great unsolved scientific problems. Unfortunately, Klein and Edgar don't bring its solution any nearer. Still, if what you need is a state-of-the-art survey of the hard facts of human evolution, they surely provide that. Just take some of the conclusions they draw from those facts with the proverbial grain of salt.