Mitochondrial DNA and the First Americans
Scholars are by no means agreed about exactly when the earliest Americans arrived. Most do agree that Alaska, then enlarged and connected to Asia by the lands now drowned by the Bering and Chukchi seas, is the only feasible route for early tribes to cross from the old world to the new.
Studies of tooth characteristics, genetics, and languages all suggest that these earliest immigrants arrived in three separate waves. First were the Paleo-Indians, whose descendants include all of the South American and Central American Indians, as well as most of those in the forty-eight states. They were followed by the Na-Dene, ancestors of the Athabaskans, of the tribes of the Pacific Northwest, and of the Navajo and Apache of the Southwest. The final wave included the Inuit and the Aleut.
There is still a good deal of argument about dates. Many South American anthropologists feel they have evidence for human occupation much earlier than anything generally accepted from Alaska or from North America in general. But even without assuming migrants before about fourteen thousand years ago, there remains the question of how the three waves of immigrants are related to each other, both in terms of origin and in terms of time, and when the Inuit and Aleut groups split apart. Some scholars suggest that all three groups arrived between fourteen thousand and twelve thousand years ago; others would spread their arrival times apart by as much as six thousand years. And the question of how the three groups are related to each other and to possible descendants of their ancestors who remained in Asia is wide open.
Dr. Gerald Shields at the Institute of Arctic Biology, University of Alaska Fairbanks, is applying a new technique to the problem. He believes that the same mitochondrial DNA (deoxyribonucleic acid) that was used to deduce a common maternal ancestress for the human race might be useful over a shorter time scale to help untangle the relationships among the earliest Americans.
Mitochondrial DNA is passed from mother to child, and changes very slowly and at a fairly constant rate over time. All of the female-line descendants of a given woman will thus have the same mitochondrial DNA at first, but as thousands and tens of thousands of years go by, slight differences will begin to develop. So long as one group is not stealing women from another, groups will similarly diverge. Because the rate of divergence is fairly constant, the length of time back to the point of separation can be estimated.
Dr. Shields' current work is based on attempting to determine the relationships among the groups still in Alaska: the Na-Dene, Inuit, and Aleut peoples. If the technique is able to separate these three groups, perhaps someday it could be extended to include the descendants of Paleo-Indian immigrants, or even Asian peoples that might be related to the first inhabitants of the Americas.
