"Ancestors of today's Native Americans populated the Great Plains about 14,000 years ago, about the time glaciers of the last Ice Age began melting back to the north. Prehistoric people living on the dry plains east of the Rocky Mountains were hunter-gatherers--they moved from place to place in search of animals to hunt and seeds, roots, and berries to gather. Archaeologists have reconstructed the history of these hunter-gatherers by studying old...