III.

Physical Traits

Native Americans are physically most similar to Asian populations and appear to have descended from Asian peoples who migrated across the Bering Strait land bridge during the part of the Quaternary period known as the Ice Age, beginning perhaps some 30,000 years ago. Like other peoples with Mongolian characteristics, Native Americans tend to have light-brown skin, brown eyes, and dark, straight hair. They differ from Asians, in the classification of races however, in their characteristic blood types. Because many Native Americans today have had one or more European-Americans or African-Americans among their ancestors, numerous people who are legally and culturally Native American may look fairer or darker than Mongolian peoples or may have markedly non-Mongolian facial features.

Over the thousands of years that indigenous peoples have lived in the Americas, they have developed into a great number of local populations, each differing somewhat from its neighbours. Some populations (such as those on the Great Plains of North America) tend to be tall and often heavily built, whereas others (for example, many in the South American Andes and adjacent lowlands) tend to be short and broad-chested; furthermore, every population includes people who vary from the average. Some physical characteristics of Native American populations have been influenced by diet or by the environmental conditions of their societies. For example, the short stature of some native Guatemalans seems to result at least in part from diets poor in protein; the broad chests and large hearts and lungs of native Andeans represent an adaptation to the rarefied atmosphere of the high mountains they inhabit.