Public Release: 

Is the evidence for human 'replacement' really clear?

Arizona State University

The common "textbook" view in paleoanthropology of when and how modern humans came to be in Western Europe sees a migration of modern humans coming from Africa through the Middle East sometime between 50,000-40,000 years ago. In this view, these "tropical" modern humans were physically and culturally distinct from the cold-adapted, culturally primitive Neandertals who were already there, and the invaders drove the older inhabitants to extinction in fairly short order. Paleoanthropologists and archaeologists cite a shift in the fossil evidence and the sudden appearance of art and tool making as evidence of the change.

But is the evidence really so clear? Not at all, says Arizona State University paleoanthropologist Geoffrey Clark. Far from being a clear shift in fossils and archaeological material documenting a relatively abrupt replacement of one species by another in the European landscape, the accumulating evidence, particularly in archaeology, "is increasingly one of geographical and behavioral mosaics." The archaeological evidence, Clark says, shows that many of the "traits" that have been traditionally associated with modern humans, such as increased sophistication and specialization in tool industries and the appearance of symbolic behavior manifest as 'art', can, in fact date much further back, depending on the locality, and can also be associated with Neandertal fossils as well as with those of modern humans. Conversely, evidence of 'more primitive' behaviors, such as the use of stone "flake" tool technology (commonly described as Mousterian as opposed to more sophisticated "blade" stone tool technology, commonly described as Aurignacian) seems to persist both before and long after the accepted "transition" boundary, again depending on locality.

"These changes really follow a much more complex temporal and spatial mosaic pattern," said Clark. "They don't show up in Europe in a neat package at around 40,000 years ago, as textbook generalizations would have it."

Clark sees a possible alternative cause for the cultural and technological changes (in both modern human and Neandertal populations) in adaptive behaviors brought on by changes in population density. In particular, more evidence for symbolic behavior, including the production of art and more formal stone tools, might have been selected for under conditions where human and/or Neandertal populations achieved a critical density, Clark argues.

"There were probably localized human population increases during the mild climatic conditions of late Oxygen Isotope Stage 3 (57,000-24,000 years ago) that could correspond with some of the isolated incidences we see of symboling", Clark said.

"Similarly, when much of northern Europe became glaciated during Oxygen Isotope Stage 2 (24,000-12,000), population packing certainly must have occurred in Southern Europe that would have intensified selection for these behaviors and that accounts for the dramatic increase that we see in the incidence of 'art' in the archaeological record. We need to remember that during much of the time that Neandertals occupied Europe the environment was intermittently pretty harsh and population density was, apparently, always very low," he said.

Clark recognizes no correlations whatsoever between particular 'types' of humans and particular 'types' of archaeological remains, either in Europe or anywhere else. He thinks that symbolism is an emergent property found in even the earliest hominids, and that it is uncorrelated with a particular human species or subspecies.

Clark notes that many archaeologists and paleoanthropologists don't seem to recognize that the lack of a strong record of a behavior does not mean that it was absent, only that it was not present with enough frequency to show up in the archaeology.

"If some combination of social, environmental and/or demographic conditions doesn't select heavily for a particular behavior, then there will be no evidence for it," he said. "It's no accident that the 'art' is concentrated when -- after 20,000 years ago -- and where -- in southwest France, northern Spain -- it is. These southern refuge areas were the only places people could go under glacial maximum conditions. "What we see in the allegedly 'sudden changes' in tool technology and 'art' in the Upper Paleolithic could very well be due to changes in population densities that increased selective pressure for the expression of symbolic behavior to the extent that it became visible archaeologically for the first time."



Note: this release relates to material to be discussed in the 8 a.m. February 15 AAAS press briefing, the 9 a.m. session, "The Archaeology of Modern Human Origins," and a paper to be given by Lawrence Straus and Geoffrey Clark entitled "When Anatomy and Archeology Do Not Coincide at 'The Transition'."

Source: Geoffrey Clark, 480-965-7596,

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