In this scenario, modern humans did not out-compete their brethren or wipe them out by means of war, but simply that they intermixed with them and, as the climate changed and the selection pressures of maintaining the bulky Neandertal form changed, two things happened: negative selection was placed on the Neandertal genome and the influx of the modern human genome swamped that of the Neandertals. To be sure, there were likely refugia and it is possible that Zafarraya (which has a full suite of Neandertal characteristics at 26 Ky BP) represents this, but it is an explanation which has a good deal going for it.
The paper “Modeling Human Ecodynamics and Biocultural Interactions in the Late Pleistocene of Western Eurasia” is co-authored by Julien Riel-Salvatore, an assistant professor of anthropology at the University of Colorado Denver; John Martin “Marty” Anderies, an associate professor of computational social science at ASU in the School of Human Evolution and Social Change and the School of Sustainability; and Gabriel Popescu, an anthropology doctoral student in the School of Human Evolution and Social Change at ASU.
“It’s been long believed that Neanderthals were outcompeted by fitter modern humans and they could not adapt,” said Riel-Salvatore. “We are changing the main narrative. Neanderthals were just as adaptable and in many ways, simply victims of their own success.”
The interdisciplinary team of researchers used archeological data to track behavioral changes in Western Eurasia over a period of 100,000 years and showed that human mobility increased over time, probably in response to environmental change. According to Barton, the last Ice Age saw hunter-gathers, including both Neanderthals and the ancestors of modern humans, range more widely across Eurasia searching for food during a major shift in the Earth’s climate.
As Dave Frayer put it, you can find individual Neandertal traits in early modern humans but no one person has the whole suite of them.
The paper can be found at http://dx.doi.org/10.1007/s10745-011-9433-8
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