Americans are physically most similar to Asian populations
and appear to have descended from Asian peoples who migrated
across the Bering land bridge during the Pleistocene Epoch,
also known as the Ice Age, beginning perhaps some 30,000
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other peoples with Mongolian characteristics, Native Americans
tend to have light brown skin, brown eyes, and dark, straight
hair. They differ from Asians, however, in their characteristic
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.
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 neighbors.
populations (such as those on the Great
Plains of North America) tend to be tall and often heavy
in build, whereas others (for example, many in the South
American Andes and adjacent lowlands) tend to be short and
broad chested; furthermore, every population includes persons
who vary from the average.
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
low-oxygen atmosphere of the high mountains they inhabit.