The Dawn of Human Culture (31 page)

years ago. Sungir’ lies 210 kilometers (125 miles) northeast of Moscow in a region that was unoccupied before the Upper Paleolithic, and its location alone highlights a newly developed human ability to adapt to especially harsh circumstances. The Sungir’ people surely invested a lot 08 Nature or Nurture.r.qxd 1/29/02 5:06 PM Page 266

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of time in finding food and in keeping warm, yet they managed to produce no less than thirteen thousand beads, three thousand of which occurred in the grave of an adult male and ten thousand of which were about equally divided between the bodies of two children buried head to head in a second, common grave. The beads occur in strands that were probably fastened to leather clothing, and they are accompanied by other art objects that suggest a burial ritual and a concern or respect for the deceased that living humans commonly share. The Sungir’

graves are in fact among the oldest from which such ritual and respect can be unambiguously inferred, but White goes further. The ten thousand beads in the children’s grave took more than ten thousand person-hours to produce, and their abundance may mean that the children occupied a special position or status in Sungir’ society.

In Chapter 1, we described how the exchange of ostrich eggshell beads fostered social cohesion among historic southern African hunter-gatherers. With ethnographic observations like this in mind, White argues that “the rapid emergence of personal ornamentation [in the Upper Paleolithic] may have marked, not a difference in mental capacities between Cro-Magnons and Neanderthals, but rather the emergence of new forms of social organization that facilitated and demanded the communication and recording of complex ideas.” In his view, either an increase in population density or a greater tendency for people to gather in large groups could have precipitated the underlying social transformation.

Archeologist Ofer Bar-Yosef of Harvard University offers a different, but complementary hypothesis. Bar-Yosef specializes in the archeology of southwestern Asia (the Near East) and he has investigated both the origin of modern humans and the origin of agriculture, 08 Nature or Nurture.r.qxd 1/29/02 5:06 PM Page 267

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which occurred about 30,000 years later. He refers to both events as

“revolutions,” and he believes that they were driven by similar forces.

About 11,000 years ago, hunter-gatherers along the eastern margin of the Mediterranean Sea relied heavily on wild cereals (wheat, barley, and rye) and other plant foods, much as their forebears had in the preceding millennia. Their adaptation was stable, and it even allowed for a degree of sedentary life—permanent or semi-permanent hamlets from which the people could exploit abundant wild plants and an accompanying supply of gazelles and other wild animals. Then, starting about 11,000 years ago, climate turned suddenly and sharply colder and drier, and the downturn persisted for 1300 years, during what paleoclimatologists call the Younger Dryas period. Wild cereals and other key food plants became much scarcer, and Bar-Yosef and other archeologists believe that the people responded by encouraging them to grow in nearby fields. To produce the next crop, they naturally selected seeds from those individual plants that grew best under their care, and in the process they transformed wild species that could grow on their own into domesticates that required human assistance. By 9500 years ago, they had added animals (sheep, goats, cattle, and pigs) to the repertoire of domesticates, and they were full-fledged farmers.

The economic transformation encouraged human population growth, and for this reason alone, it also promoted changes in social and economic relations. As population density increased and world climate ameliorated after 9000 years ago, splinter groups broke off to seek new land and they eventually spread the new agricultural way of life westwards to Spain and eastwards to Pakistan.

Bar-Yosef suggests that like the agricultural revolution, the much earlier event we call the “dawn of human culture” involved the 08 Nature or Nurture.r.qxd 1/29/02 5:06 PM Page 268

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invention of new ways to obtain food and that this resulted in population growth and in new modes of social and economic organization.

Splinter groups would again have carried the new adaptation from its core area, which in this case was probably eastern Africa.

Like White and Bar-Yosef, other archeologists have proposed models in which the “dawn” followed naturally on a technological advance, a change in social relations, or both. Such explanations are attractive in part because they rely on the same kind of forces that historians and archeologists routinely use to explain much more recent social and cultural change. In regard to the “dawn,” however, they share a common shortcoming: they fail to explain why technology or social organization changed so suddenly and fundamentally.

Population growth is an inadequate reason, first, because it too would have to be explained, and second, because there is no evidence that population was growing anywhere just prior to the “dawn.” We have noted that the Africans who lived just before the “dawn” made MSA (Middle Stone Age) artifacts, while those who lived afterwards produced LSA (Later Stone Age) assemblages. In southern and northern Africa, the interval between 60,000 and 30,000 years ago that encompasses the MSA/LSA transition appears to have been mostly very arid, and human populations were so depressed that they are nearly invisible to archeology. Conditions for human occupation remained more favorable in eastern Africa, but so far, excavations and surveys here also fail to suggest a population increase in the late MSA. Neither the number of sites nor the density of occupation debris they contain increase conspicuously towards the LSA, which began between 50,000

and 40,000 years ago. And in Europe populations grew only after the

“dawn” arrived, not in anticipation of it.

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Conceivably, the trigger was a climatic event like the Younger Dryas of 11,000 years ago, but the “dawn” occurred during a long interval of fluctuating climate that on present evidence did not include a comparably dramatic episode. Even if one is eventually detected, it will be difficult to explain why it prompted such a far-reaching behavioral response, when yet earlier, equally or even more radical climatic spikes did not. The most notable preceding spike was a millennium-long bout of intense cold that followed the Mt. Toba volcanic supereruption in Sumatra, Indonesia, about 73,500 years ago. The Mt. Toba eruption was the most massive in the last 2 million years and perhaps in the last 450 million years. To provide perspective, Toba ejected roughly four thousand times as much material as Mt. St. Helens (Washington State) in 1981 and about forty times more than Mt. Tambora (Sumbawa Island, Indonesia) in 1815. The Tambora eruption was the largest in historic times, and the aerosols from it reduced sunlight and global temperatures so much that 1816 became known as “the year without a summer” when New England experienced snow in July and August. The far more extensive aerosols from Toba produced a “volcanic winter” akin to the “nuclear winter” that some have hypothesized would follow a new world war, and the effect was accentuated and prolonged by feedback from a global trend toward colder climate in the early part of the last glacial period. Plant and animal populations must have declined sharply almost everywhere, and the impact on human populations was probably catastrophic. Yet, the aftermath of Mt. Toba is notable precisely because it did not provoke a revolutionary cultural response. The lack of a response supports artifactual evidence that people possessed limited ability to innovate before 50,000 years ago.

Finally, there is no evidence that the “dawn” was prompted by a technical innovation comparable to the invention of agriculture.

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Archeology not only fails to reveal such an innovation, it suggests that the “dawn” actually marks the beginning of the human ability to produce such remarkable innovations. From an archeological perspective then, the “dawn” is not simply the first in a series of ever more closely spaced “revolutions,” starting with agriculture and running through urbanization, industry, computers, and genomics, it was the seminal revolution without which no other could have occurred. This brings us to what we think was the key change that explains it.

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“dawn” is that it stemmed from a fortuitous mutation that promoted the fully modern human brain. Our case relies primarily on three circumstantial observations extracted from our preceding survey of human evolution. The first is that natural selection for more effective brains largely drove the earlier phases of human evolution. The neural basis for modern human behavior was not always there; it evolved, and we are merely using the available behavioral evidence to suggest when.

The second observation is that increases in brain size and probably also changes in brain organization accompanied much earlier behavioral/ecological shifts. These include especially the initial appearance of stone artifacts 2.6 to 2.5 million years ago, the first appearance of hand axes and the simultaneous human expansion into open, largely treeless environments 1.8 to 1.6 million years ago, and possibly also the advent of more sophisticated hand axes and the first permanent occupation of Europe about 600,000 to 500,000 years ago.

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Our third and final observation is that the relationship between anatomical and behavioral change shifted abruptly about 50,000 years ago. Before this time, anatomy and behavior appear to have evolved more or less in tandem, very slowly, but after this time anatomy remained relatively stable while behavioral (cultural) change accelerated rapidly. What could explain this better than a neural change that promoted the extraordinary modern human ability to innovate? This is not to say that Neanderthals and their non-modern contemporaries possessed ape-like brains or that they were as biologically and behaviorally primitive as yet earlier humans. It is only to suggest that an acknowledged genetic link between anatomy and behavior in yet earlier people persisted until the emergence of fully modern ones and that the postulated genetic change 50,000 years ago fostered the uniquely modern ability to adapt to a remarkable range of natural and social circumstances with little or no physiological change.

Arguably, the last key neural change promoted the modern capacity for rapidly spoken phonemic language, or for what anthropologists Duane Quiatt and Richard Milo have called “a fully vocal language, phonemicized, syntactical, and infinitely open and productive.”

In the 4 October 2001 issue of
Nature
magazine, a team of geneticists led by Cecilia Lai of Oxford University indirectly supported this idea when they identified a single gene that is probably “involved in the developmental process that culminates in speech and language.”

Individuals who possess a defective copy of this gene have great difficulty recognizing basic speech sounds, learning grammatical rules, and understanding sentences. They are not necessarily impaired in other respects, and they often score normally for non-verbal intelligence. In short, the new discovery shows that a single mutation could underlie 08 Nature or Nurture.r.qxd 1/29/02 5:06 PM Page 272

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the fully modern capacity for speech. Still, we stressed earlier that there is no compelling anatomical evidence for the evolution of language, and the suggestion that its final development underlay the “dawn” follows mainly from the intimate bond between language and culture among living humans. Living people use language not only for communication, but also for mental modeling and for posing the kind of

“what if” questions that enable the uniquely modern human ability to innovate. And in our view, it is above all a quantum advance in the human ability to innovate that marks the dawn of human culture.

The strongest objection to the neural hypothesis is that it cannot be tested from fossils. The connection between behavioral and neural change earlier in human evolution is inferred from conspicuous increases in brain size, but humans virtually everywhere had achieved modern or near-modern brain size by 200,000 years ago. Any neural change that occurred 50,000 years ago would thus have been strictly organizational, and fossil skulls so far provide only speculative evidence for brain structure. Neanderthal skulls, for example, differ dramatically in shape from modern ones, but they were as large or larger, and on present evidence, it is not clear that the difference in form implies a significant difference in function. There is especially nothing in the skull to show that Neanderthals or their contemporaries lacked the fully modern capacity for language.

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support for an abrupt replacement grew stronger in succeeding decades, but it became particularly compelling after the middle 1980s with the development of three new, crucial lines of evidence. First were new dates which showed that modern or near-modern humans inhabited Africa between 120,000 and 50,000 years ago when only the Neanderthals lived in Europe. Second were new fossils (mainly from the Sima de los Huesos at Atapuerca, Spain) which showed that the Neanderthals evolved in Europe between about 400,000 and 130,000

years ago. And third were increasingly sophisticated genetic analyses which show that the Neanderthals diverged from living humans long before living human groups diverged from one another. Some of the new (and old) evidence is ambiguous, circumstantial, or even contra-dictory, but this is inevitable in historical science, which has more in common with a criminal trial than it does with a physics experiment.