"The Upper Paleolithic," according to Stanford anthropologist Richard Klein, "signals the most fundamental change in human behavior that the archaeological record may ever reveal, barring only the primeval development of those human traits that made archaeology possible."3
He's not kidding. The archaeological record of the Upper Paleolithic, or last phase of the Old Stone Age—the product of the modern humans who displaced the Neanderthals in Europe 30,000 to 40,000 years ago—is qualitatively different from anything that came before. With the advent of modern humans in Europe, innovation was bustin' out all over.
Many of the new features that marked this "great leap forward" were impressive—cave paintings, sculpture, jewelry, dramatically improved tools and weapons. Some of them brought significant changes in the practical matters of daily life, but most important, from our point of view, is that they show an extraordinary increase in the human capacity to create and invent.
What's more, the innovations show that profound social and cultural changes were taking place. We developed new social arrangements as well as new tools: The spearpoints and scrapers of this period often used materials from hundreds of miles away, which must have been acquired through some form of trade or exchange. Before, tools were almost entirely made from local materials. We also see the beginnings of cultural variation: Tools and weapons started showing regional styles.
At this point, people—some of them anyhow—were acting wildly different from their forebears of even 20,000 years earlier. The spark of innovation was taking them in all kinds of new directions. We're not saying that every Tom, Dick, and Harry was an inventor, but at least some people were coming up with new ideas—and doing so perhaps 100 times more often than in earlier times. The natural question is, "Why?" It doesn't really look as if being a modern human, in the sense of having ancestors who were anatomically modern and who had originated in Africa, was enough, by itself, to trigger this change. We don't see this storm of innovation in Australia. Obviously, something important, some genetic change, occurred in Africa that allowed moderns to expand out of Africa and supplant archaic sapiens. Equally obviously, judging from the patchy transition to full behavioral modernity, there was more to the story than that. So probably being an "anatomically modern" human was a necessary but not sufficient condition for full behavioral modernity.
More generally, behavior has a physical substrate: Biology keeps culture on a leash, which is why you can't teach a dog to play poker, never mind all those lying paintings. We have every reason to think that back in the Eemian period (the interglacial period of about 125,000 years ago), the leash was too short for agriculture. Humans did not develop agriculture anywhere on earth during the Eemian, but they did so at least seven times independently in the Holocene, the most recent interglacial period, which began 10,000 years ago. Not only that, in the Eemian the leash was too short to allow for the expansion of anatomically modern humans out of Africa into cooler climates. In that period, biology somehow kept people from making at-latls or bows, and from sewing clothes or painting, all of which are routinely performed and highly valued by contemporary hunter-gatherers. People were different back then—significantly different, biologically different.
Genetic changes allowed important human developments in 40,000 BC that hadn't been possible in 100,000 BC. Moreover, other genetic changes may have been necessary precursors to later cultural changes. Here we shall argue that the dramatic cultural changes that took place in the Upper Paleolithic, which have been referred to as the "human revolution," the "cultural explosion," or (our favorite), the "big bang," occurred largely because of underlying biological change.
We are not the first to suggest this. Richard Klein has said that some mutation must have been responsible for this dramatic increase in cultural complexity.4 We wholly agree with the spirit of his suggestion, but we believe that such dramatic change probably involved a number of genes, and thus some mechanism that could cause unusually rapid genetic change. As it turns out, we know of such a mechanism, and the necessary circumstances for that mechanism turn out to have arrived just in time for the human revolution.
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