Richard G. Klein (born April 11, 1941) is a Professor of Biology and Anthropology at Stanford University. He is the Anne T. and Robert M. Bass Professor in the School of Humanities and Sciences. He earned his PhD at the University of Chicago in 1966, and was elected to the National Academy of Sciences in April 2003. His research interests include paleoanthropology, Africa and Europe. His primary thesis is that modern humans evolved in East Africa, perhaps 100,000 years ago and, starting 50,000 years ago, began spreading throughout the non-African world, replacing archaic human populations over time. He is a critic of the idea that behavioral modernity arose gradually over the course of tens of thousands, hundreds of thousands of years or millions of years, instead supporting the view that modern behavior arose suddenly in the transition from the Middle Stone Age to the Later Stone Age around 50-40,000 years ago.
