Uploaded on Nov 20, 2011
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The well-established "Out of Africa" model asserts that all living humans are the descendants of Africans who immigrated, well, out of Africa 50,000 years ago. But did the behavioral shift that led to this immigration -- and that, indeed, underlies advanced human behavior today -- originate culturally and gradually or genetically and abruptly? World renowned anthropologist Dr. Richard Klein explores new and old evidence that sheds light on this challenging and divisive question.
Twenty-three years ago, a landmark exploration of mitochondrial DNA diversity popularized the idea of a recent African origin for all living humans. The ancestral African population was estimated to have existed 200 ka (thousands of years ago), plus or minus a few tens of thousands of years. A corollary was that at some later date, its fully modern African descendents expanded to swamp or replaced the Neanderthals and other non-modern Eurasians. The basic concept soon became known as "Out of Africa," after the Academy Award winning film (1985) that took its title in turn from Isak Dinesen's classic autobiography (1937). Many subsequent genetic analyses have reaffirmed the fundamental Out-of-Africa model, and the fossil and archaeological records also support it strongly. The fossil record implies that anatomically modern or near-modern humans were present in Africa by 150 ka, and the fossil and archaeological records together indicate that modern Africans expanded to Eurasia beginning about 50 ka.
Most paleoanthropologists now accept Out of Africa, and they argue mainly over the extent to which non-modern Eurasians and modern African immigrants may have interbred. Most authorities further agree that a behavioral transformation underlay the modern African expansion, but they presently divide between a majority who believe that advanced behaviors accumulated gradually between perhaps 120 and 50 ka and a minority who believe they appeared abruptly about 50 ka. Those who favor gradual development usually attribute it to long-term social, demographic, or economic shifts, while whose those who perceive abrupt development suggest that it was prompted by genetic change. My main purpose here is to summarize the evidence for the sociodemographic and genetic alternatives and to explain why I prefer the genetic explanation. Its principal failing has long been that it could not be evaluated independently of the archaeology that suggests it, but modern and ancient DNA now promise a direct test.
Dr. Richard G. Klein is the Anne T. and Robert M. Bass Professor in the School of Humanities and Sciences and Professor of Anthropology and Biology at Stanford University. Professor Klein researches the archaeological and fossil evidence for the evolution of human behavior. He has done fieldwork in Spain and especially in South Africa, where he has excavated ancient sites and analyzed the excavated materials since 1969. He has focused on the behavioral changes that allowed anatomically modern Africans to spread to Eurasia about 50,000 years ago, where they swamped or replaced the Neanderthals and other non-modern Eurasians.
This talk is sponsored by Cal Poly's College of Liberal Arts, Social Sciences Department, and The Forum at Poly