BOSTON, MASS.- Some unique behaviors associated with modern humans--including a shift in diet and the earliest evidence of personal ornaments like beads--may be linked to an increase in human population density between 40 and 50 thousand years ago, Mary C. Stiner and Steven L. Kuhn reported today at the American Association for the Advancement of Science (AAAS) meeting.
Their study could shed light on the origin of modern humans, a contentious topic in anthropology. Some researchers think that modern humans arose as a new species in Africa around 200,000 years ago, subsequently migrating out of Africa and replacing earlier groups of humans around the world. Other researchers believe that early human populations like the Neanderthals gradually evolved into modern humans, while still others think there may be evidence of some intermingling between early and modern human populations.
Genetic, fossil, and archaeological evidence have been used to support each scenario, but archaeological data provide a unique approach to the problem, said Stiner.
"The nice thing about archaeology, something that's missing from fossil and genetic data, is that we have fairly refined information on the age and geographic location of our evidence. This level of detail in time and space has never been worked out for the genetic or fossil evidence," Stiner noted.
Stiner and Kuhn's research indicates that modern human behavior appeared at the same time in many parts of the world. Ornament traditions, in particular, seem to have developed simultaneously in Africa, Asia, and Europe, "suggesting that this phenomenon does not mark the geographic expansion of a single population," said the University of Arizona scientists.
The researchers investigated several Upper Paleolithic sites around the Mediterranean Basin to look for aspects of the archaeological record that might record evidence of modern human behavior. Their analysis uncovered a significant shift in the types of small game animals hunted or gathered at these sites, from slow-reproducing and easy-to-catch animals like shellfish and tortoises, to quickly-reproducing and more agile animals like birds, hares, and rabbits.
Stiner and Kuhn think the switch might reflect an increase in human population density, which would have placed more pressure on available resources and forced the humans to expand their dietary repertoire.
"If you have over-used your preferred resource, you can respond by turning to lower-ranked resources. We have pretty clear evidence that that's what was going on after about 40 to 50 thousand years ago," said Stiner told the AAAS attendees.
Along with the shift in small game use, recent excavations of Upper Paleolithic sites such as Üçagizli Cave in Turkey (WEBSITE: http://w3.arizona.edu/~hatayup) and Ksar' Akil in Lebanon revealed an "unprecedented proliferation" of personal ornaments like shell beads and pendants. The upswing in personal ornamentation might be a sign of Paleolithic population increases as well, said Stiner and Kuhn.
"Ornamentation is universal among all modern human foragers," said Stiner, noting that these groups use the ornaments to convey information about kinship, status, and other aspects of identity to outsiders.
The timing of these two behavioral changes, long after the first appearance of anatomically modern humans in the fossil record, "makes it clear that modern human behavior doesn't appear at the same time that skeletally modern humans do," Stiner concluded.
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