EARLY HUMAN EVOLUTION IN THE AMERICAS: TIMING, GEOLOGY, AND ECOLOGY

Deglaciation at the end of the LGM probably controlled the timing of human entry into the Americas. Deglaciation was not sufficiently advanced to permit human colonization until about 14,000 14C BP (16,800 cal BP) along the NW coast of N America, and possibly as late as about 11,000 to 11,500 14C BP (12,550 - 13,050 cal BP) in the interior. Minimum limiting dates for New World human remains suggest that colonization occurred shortly after the LGM, c. 14,000 14C BP (16,250 cal BP) or 15,000 14C BP (16,950 cal BP). Thus, the oldest human remains from the Americas are modern Homo sapiens. No early archaic human forms, such as Homo erectus, have been discovered in the Americas. The oldest human skeletons (>8,000 14C BP) found in the Americas tend to have longer and narrower (dolichocephalic) crania, while later human remains tend to have broader (brachycephalic) crania which more closely resemble Asian Mongoloid populations. Rapid evolutionary change or multiple migrations to the Americas could explain these differences. Because the Americas were the last major continents to be colonized by humans, evolutionary studies in the Americas focus primarily on cultural and technological development rather than biological evolution. The preponderance of linguistic, biological and archeological evidence indicates Native Americans probably originated in northeast Asia. Reliably dated archeological sites document humans occupying a variety of habitats throughout the Americas by 11,500 14C BP (12,550 - 13,100 cal BP). Ecological settings, isotope analysis of human skeletal remains, and trace element analysis of obsidian artifacts demonstrate maritime and terrestrial adaptations by c. 11,000 14C BP (12,550 cal BP). The adaptations of the founding New World population had a profound impact on New World environments and American environments in turn helped shaped subsequent cultural development in the Americas.