The pattern of intermittent technological innovation was gone, replaced by constant refinement.

Clearly, these people were us.

idence of any intermixing of peoples in Europe.

In the Levant, the coexistence ceased— after about 60,000 years or so—at right about the time that Upper Paleolithic-like tools began to appear. About 40,000 years ago the Neandertals of the Levant yielded to a presumably culturally rich H. sapiens, just as their European counterparts had.

The key to the difference between the European and the Levantine scenarios lies, most probably, in the emergence of modern cognition—which, it is reasonable to assume, is equivalent to the advent of symbolic thought. Business had continued more or less as usual right through the appearance of modern bone structure, and only later, with the acquisition of fully modern behavior patterns, did H. sapiens become completely intolerant of competition from its nearest—and, evidently, not its dearest— co-inhabitors.

To understand how this change in sensibility occurred, we have to recall certain things about the evolutionary process. First, as in this case, all innovations must necessarily arise within preexisting species—for where else can they do so? Second, many novelties arise as "exap-tations," features acquired in one context before (often long before) being co-opted in a different one. For example, hominids possessed essentially modern vocal tracts for hundreds of thousands of years before the behavioral record gives us any reason to believe that they employed the articulate speech that the peculiar form of this tract permits.

And finally, it is important to bear in mind the phenomenon of emergence— the notion that a chance coincidence gives rise to something totally unexpected. The classic scientific example in this regard is water, whose properties are wholly unpredicted by those of hydrogen and oxygen atoms alone. If we combine these various observations, we can see that, profound as the consequences of achieving symbolic thought may have been, the process whereby it came about was unexceptional.

We have no idea at present how the modern human brain converts a mass of electrical and chemical discharges into what we experience as consciousness. We do know, however, that somehow our lineage passed to symbolic thought from some nonsymbolic precursor state. The only plausible possibility is that with the arrival of anatomically modern H. sapiens, existing exaptations were fortuitously linked by a relatively minor genetic innovation to create an unprecedented potential.

Yet even in principle this deduced scenario cannot be the full story, because anatomically modern humans behaved archaically for a long time before adopting modern behaviors. That discrepancy may be the result of the late appearance of some key hardwired innovation not reflected in the skeleton, which is all that fossilizes. But this seems unlikely, because it would have necessitated a wholesale Old World-wide replacement of hominid populations in a very short time, something for which there is no evidence.

It is much more likely that the modern human capacity was born at—or close to—the origin of H. sapiens, as an ability that lay fallow until it was activated by a cultural stimulus of some kind. If

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