First Americans Arrived Earlier Than Once Thought
Christopher Columbus may have introduced Europe to the New World, but he could have called it the Pretty Old World. New research is supporting the idea that humans first entered the Americas -- across a land bridge connecting modern-day Alaska and Siberia -- thousands of years earlier than scientists had believed, perhaps substantially more than 20,000 years ago. Discoveries in archaeology, linguistics, and even genetics reveal that the story of the first Americans is a very old and intricate tale."The bottom line is that the peopling process is a lot more complex than we ever thought it was," said archaeologist Tom Dillehay of the University of Kentucky. Researchers had developed a neat picture of people migrating in well-timed waves from Asia into the Americas -- arriving sometime around 11,500 years ago. Now, scientists are realizing that the picture isn't quite so organized.
"For a long time, it was too simple," said David Meltzer, an archaeologist at Southern Methodist University in Dallas. "Armies move in waves. Hunter-gatherer groups don't move in waves." The new studies suggest that the first Americans probably crossed the land bridge earlier than 20,000 years ago, before great ice sheets sealed off the passageway for thousands of years. And some people may have even wandered across much earlier.
For example, new work indicates that it would have taken close to 40,000 years for the language of the first Americans to diversify into the 140 or so language families seen today among Native Americans. And other research, into the genetic relationships between Native Americans and several Asian groups, suggests that the earliest split between these groups could have occurred more than 30,000 years ago. The picture of more-ancient Americans first gained wide acceptance a year ago, when a team of archaeologists journeyed to southern Chile to visit the site known as Monte Verde. Dillehay and his colleagues have been excavating the site since 1977, and they have long said that it is the remains of a human settlement from 12,500 years ago. But many archaeologists were reluctant to accept that date, because it contradicted the notion that the first record of American settlement was a collection of 11,500-year-old spear points found far north of Monte Verde, near Clovis, N.M.
Last year, the team, sponsored in part by the Dallas Museum of Natural History and the National Geographic Society, went to Monte Verde and agreed that it was indeed older than Clovis. That implied that humans had not only made it to the Americas by 12,500 years ago -- they had also managed to get all the way to southern South America from their entry point in Alaska. And that was quite a task, unless they arrived much earlier, because the land bridge was sealed off by ice from about 13,000 to about 20,000 years ago.
So now scientists are thinking that people must have made it across before ice covered the passageway. And the Monte Verde discovery is prompting other archaeologists to look for sites that may also be pre-Clovis. "Within the past year, the green light's gone on," said Dennis Stanford, an archaeologist at the Smithsonian Institution in Washington, D.C. "There are a number of sites that looked good at first blush" to be older than Clovis, he added. Some of those include the Cactus Hill site in southeastern Virginia, which may contain archaeological remains from 15,000 years ago; the Chesrow complex in eastern Wisconsin, which appears to have human-made artifacts buried alongside 13,000-year-old mammoths; and the Meadowcroft rock shelter near Pittsburgh, which may date to 14,000 years ago. (There are even hints of a 33,000-year-old layer of human artifacts at Monte Verde, Dillehay said, a prospect he said he doesn't even want to consider at the moment, although he plans to excavate it in 2001.)
Many archaeologists have argued for pre-Clovis dates for some of these sites for years, but others have pointed out problems with the techniques used to date the artifacts, or have questioned whether the artifacts were really made by people. Other scientists caution against jumping to re-date other sites. "Just because Monte Verde is older doesn't mean the other sites have to be," Meltzer said.
Along with archaeological evidence, more clues to the earliest Americans come from linguistic studies done by Johanna Nichols of the University of California, Berkeley. Nichols has studied the 140 or so language families that encompass Native American languages today, then projected them back in time to study how long it would take for those to develop. (A language family is a group of related languages, such as the Indo-European family that includes English.) She found that it would take 30,000 years at least -- and closer to 40,000 in some instances -- to generate the number of languages seen today in the Americas, she reported.
Nichols also has calculated how long it would take for a language -- and hence the people speaking it -- to spread from Alaska to Monte Verde. A language "traveling in a beeline at a good clip" could cover that 8,000-mile distance in 7,000 years, she said. So to reach Monte Verde by 12,500 years ago, people would have had to start traveling from Alaska 19,500 years ago. But the land bridge was sealed by ice then, so the migrants would have had to enter even earlier. "All of this points to a great age" for the first entry, she said.
Similarly, geneticists have found that humans must have entered the Americas at least 30,000 years ago, reported Theodore Schurr of Emory University. Schurr and colleagues have been studying DNA and other genetic markers, from Native American and Siberian groups, to see how these people are related. Such markers are passed down through generations, so by studying which groups still have the markers -- and in what amounts -- scientists can learn how groups have separated and then intermingled.
All Native American groups have four special markers that appear to trace back to Asia, Schurr said. And modern people in Siberia have three of the four markers, plus a very small amount of the fourth. That suggests to researchers that the three markers are very old, dating from the time when Asians migrated to America; and that the fourth represents a more recent intermingling of the groups.
Other scientists are turning to biological techniques to study objects found during archaeological digs -- such as ancient hair, said Robson Bonnichsen, director of the Center for the Study of the First Americans at Oregon State University. Bonnichsen and colleagues have been studying naturally shed hair from archaeological sites to see whether it can be used to retrieve ancient DNA. His team has found that it's possible to determine the age of a hair -- through dating the decay of its radioactive carbon -- at the same time as extracting DNA from the hair. Bonnichsen reported that his group had extracted ancient DNA from a 9,400-year-old clump of hair from a desert bighorn sheep. The ancient hair, found in a cave in eastern Nevada, is genetically similar to a modern hair from a bighorn sheep, he said.
(Source: The Record (New Jersey) / by Alexandra Witze - Aug 2 1998)