For decades, scientists thought they had solved a mystery that had puzzled the likes of Thomas Jefferson and Benjamin Franklin. How did humans first reach North America? The answer - so they thought - was that people had migrated to Alaska from Siberia by walking across a "land bridge" where the Bering Strait is now.
Now, new discoveries are mystifying archaeologists again.
In 1929, a cowboy named James Ridgley Whiteman found projectile points among the bones of a mammoth (an ancient elephant) in Clovis, N.M. There were among the most ancient of Indian artifacts - about 13,000 years old. Experts believed the same people who manufactured these "Clovis points" were among the earliest to populate the Americas.
The theory made sense. The melting of glaciers at the end of the last Ice Age 13,500 years ago would have allowed people to walk from Asia to North America over a land bridge.
But then, in the 1990s, mounting evidence pointed to approximately 10 recently discovered sites in South America about the same age as the one in Clovis. One of them, in Monte Verde, Chile, was 1,000 years older. At that time, the land bridge would have been closed by impassible ice. Even so, how could humans have gotten that far south so quickly?
"The big questions about the peopling of North America are back again," says Kenneth Tankersley, a professor of anthropology at Kent State University in Kent, Ohio.
In 1996, scientists discovered Kennewick Man along the Columbia River in Washington State. It is one of the oldest (9,000 years) and most complete human skeletons found in North America. His bones resemble those of someone from Polynesia. Perhaps he, and others, reached North America by boat from Southern Asia, rather than from Russia.
The future could hold the secrets of the past. DNA technology may allow scientists to answer the questions of who the first settlers were and where they came from. DNA is a molecule that contains a chemical "blueprint" for an organism's physical traits. It can be used as a way to link ethnic groups over time.
Scientists hope to compare DNA from ancient human remains with DNA collected from populations of ethnic groups around the world. Maybe a match will solve the mystery.
(c) Copyright 2000. The Christian Science Publishing Society