One complicating factor is that there appears to be no correlation whatever between the achievement in the human lineage of behavioral modernity and anatomical modernity. We have evidence of humans who looked exactly like us in the Levant at close to 100 kyr ago. But at the same time, in dramatic contrast to what happened in Europe, the Levantine Neandertals persisted in the area for some 60 kyr after the anatomical moderns appeared. Whats more, throughout this long period of coexistence (whatever form it took, and frankly we have no idea how the different hominids contrived to share the landscape for all those millennia), as far as we can tell from the toolkits they made and the sites they left behind, the two kinds of hominid behaved in more or less identical ways. Suggestively, it was not until right around the time that Cro-Magnon-equivalent stoneworking techniques showed up in the Levant, at about 45 kyr ago, that the Neandertals finally yielded possession of the area. And it was almost certainly the adoption of symbolic cognitive processes that gave our kind the final--and, for the Neandertals, fatal--edge. The conclusion thus seems ineluctable that the emergence of anatomically modern Homo sapiens considerably predated the arrival of behaviorally modern humans. But while this might sound rather counterintuitive (for wouldnt it be most plausible to explain the arrival of a new kind of behavior by that of a new kind of hominid?), it actually makes considerable sense. For where else can any behavioral innovation become established, except within a preexisting species?
The Brain and Innovation
NOBODY WOULD DISPUTE that to understand cognitive processes in any vertebrate species, we have to look to the brain. In the case of our own family, Homo neanderthalensis was endowed with a brain as large as our own, albeit housed in a skull of remarkably different shape. And while we know from the very different archaeological records they left behind that Neandertals and Cro-Magnons behaved in highly distinctive ways, specialists on human brain evolution are hard put to identify any features on the external surface of the brain (as revealed in casts of the interior of the braincase) that would by themselves suggest any major functional difference between Neandertal and modern sapiens brains. The same is obviously true for the brains of those early sapiens whose material cultures and ways of life resembled those of the Neandertals. Clearly, then, we cannot attribute the advent of modern cognitive capacities simply to the culmination of a slow trend in brain improvement over time. Something happened other than a final physical buffing-up of the cognitive mechanism. Of course, by the time modern-looking humans came on the scene the necessary groundwork must have been laid for the adoption of modern cognitive processes, but this is not necessarily the same as saying that a specific neural mechanism had been acquired for them.
Lets look again, for a moment, at what our knowledge of the evolutionary process suggests may have occurred. First, its important to remember that new structures do not arise for anything. They simply come about spontaneously, as by-products of copying errors that routinely occur as genetic information is passed from one generation to the next. Natural selection is most certainly not a generative force that calls new structures into existence; it can only work on variations that are presented to it, whether to eliminate unfavorable variants or to promote successful ones. We like to speak in terms of adaptations, since this helps us to make up stories about how and why particular innovations have arisen, or have been successful, in the course of evolution; but in reality, all new genetic variants must come into being as exaptations. The difference is that while adaptations are features that fulfill specific, identifiable functions (which they cannot do, of course, until they are in place), exaptations are simply features that have arisen and are potentially available to be co-opted into some new function. This is routine stuff, for many new structures stay around for no better reason than that they just dont get in the way.