Human Diaspora and Extinction

Between 300,000 and 200,000 years ago, Homo sapiens evolved from H. erectus in Africa. This is the species to which modern humans belong. H. sapiens, whose fossils and artifacts are found in Europe and Asia, exhibit rounder and higher-profile skulls with a more delicately structured and flattened face, a distinctive chin, and smaller teeth and jaw. Currently, two distinct species (based on DNA and nuclear gene-mapping) of H. sapiens are known to overlap in time and space in the late Pleistocene: Neanderthals (H. neanderthalensis) and Cro-Magnon (H. sapiens). Neanderthals lived from about 150,000 to 30,000 years ago and were stocky and slightly shorter than modern humans, with relatively large cranial capacity (1350 cubic centimeters), prominent brow ridges, projecting mouth, and receding chin. They developed the Mousterian stone culture, which is characterized by more sophisticated knives and scrapers than those of earlier stone cultures. Trace fossil evidence (for example, artifacts, injuries to the bone, and positioning of the bodies) also suggests that Neanderthals cared for injured and sick members of their group and performed burial rituals. Cro-Magnons, resembling modern Europeans with a flattened brow and projecting chin, occurred from about 34,000 to 10,000 years ago. They moved into regions inhabited by the Neanderthals and, within a short span of time, the Cro-Magnon replaced them either through competition for resources (for example, food, shelter, territory) or by tribal warfare. The Cro-Magnon culture developed into the Late Neolithic culture with specialized tools, cave artwork, decorative bone carvings, clay figurines, and jewelry.

By the end of the Pleistocene, from about

30,000 to 15,000 years ago, small groups of humans began to cross into North America via the Bering Straits land bridge between what is today Russia and Alaska (Boyd and Silk, 2000). By about 12,000 years ago, when the continental glaciers were melting rapidly, many groups of humans migrated to the south via an ice-free corridor from Alaska through the northern (Canadian) Rocky Mountains into the western United States. There is evidence in the form of jaw bones, teeth, and sculpted wood and bone, that humans made their way as far south as South America, to Peru and Chile, by 12,600 years ago. The Clo-vis people, named for their archaeological sites near Clovis, New Mexico, thrived from 13,000 to 11,000 years ago and produced distinctive projectile points that are often found embedded in or associated with animal remains. From 11,000 (end Pleistocene) to 9,000 (beginning Holocene) years ago, the Folsom people fashioned finely flaked and fluted, short points that were attached to shafts. These artifacts have been found at kill sites of extinct bison. By about 10,000 years ago, humans began to raise domesticated animals and turned to agriculture as climates warmed at the end of the Pleistocene.

Two important lessons about global climate change and biodiversity can be learned from geologic, paleontologic, and geochemi-cal evidence in the Pleistocene record. First, sudden changes in climate over very short time periods, such as a warming event of several degrees centigrade in ten years, can occur without being influenced by human activities that include deforestation and the burning of fossil fuels. Second, there is evidence of a pattern of animal extinction based on human activities—mainly overhunting and, most recently, deforestation via the expansion of agriculture.

—Stephen T. Hasiotis

See also: Geology, Geomorphology, and Geography; Glaciation; Global Climate Change; Habitat Tracking; Human Evolution; Hydrological Cycle

Bibliography

Boyd, Robert, and Joan B. Silk. 2000. How Humans Evolved. New York: W. W. Norton; Condie, Kent, and Robert E. Sloan. 1998. Origin and Evolution of Earth: Principles of Historical Geology. Upper Saddle River, NJ: Prentice Hall; Imbrie, John, and Katherine P. Imbrie. 1994. Ice Ages: Solving the Mystery. Cambridge: Harvard University Press; Levin, Harold L. 1999. The Earth through Time. Fort Worth, TX: Saunders; Lowe, John J., and Michael J. C. Walker. 1997. Reconstructing Quaternary Environments. Essex: Addison Wesley Longman; Remane, Jürgen. N.d. "International Stratigraphic Chart and Explanatory Note to the International Stratigraphic Chart." Trond-heim, Norway: UNESCO, Division of Earth Sciences, and the International Union of Geological Sciences. Stanley, Steven M. 1999. Earth System History. New York: W. H. Freeman; Wicander, Reed, and James S. Monroe. 1993. Historical Geology: Evolution of the Earth and Life through Time. Minneapolis/Saint Paul: West.

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