(5 of 5)
Or at least you can try. Those molecular clocks are still rather crude. "The mitochondrial DNA signals a migration up to 30,000 years ago," says research geneticist Michael Hammer of the University of Arizona. "But the Y suggests that it occurred within the last 20,000 years." That's quite a discrepancy. Nevertheless, Hammer believes that the evidence is consistent with a single pulse of migration.
Theodore Schurr, director of the University of Pennsylvania's Laboratory of Molecular Anthropology, thinks there could have been many migrations. "It looks like there may have been one primary migration, but certain genetic markers are more prevalent in North America than in South America," Schurr explains, suggesting secondary waves. At this point, there's no definitive proof of either idea, but the evidence and logic lean toward multiple migrations. "If one migration made it over," Dillehay, now at Vanderbilt University, asks rhetorically, "why not more?"
Out of Siberia?
Genetics also points to an original homeland for the first Americans — or at least it does to some researchers. "Skeletal remains are very rare, but the genetic evidence suggests they came from the Lake Baikal region" of Russia, says anthropologist Ted Goebel of the University of Nevada at Reno, who has worked extensively in that part of southern Siberia. "There is a rich archaeological record there," he says, "beginning about 40,000 years ago." Based on what he and Russian colleagues have found, Goebel speculates that there were two northward migratory pulses, the first between 28,000 and 20,000 years ago and a second sometime after 17,000 years ago. "Either one could have led to the peopling of the Americas," he says.
Like just about everything else about the first Americans, however, this idea is open to vigorous debate. The Clovis-first theory is pretty much dead, and the case for coastal migration appears to be getting stronger all the time. But in a field so recently liberated from a dogma that has kept it in an intellectual straitjacket since Franklin Roosevelt was President, all sorts of ideas are suddenly on the table. Could prehistoric Asians, for example, have sailed directly across the Pacific to South America? That may seem far-fetched, but scientists know that people sailing from Southeast Asia reached Australia some 60,000 years ago. And in 1947 the explorer Thor Heyerdahl showed it was possible to travel across the Pacific by raft in the other direction.
At least a couple of archaeologists, including Dennis Stanford of the Smithsonian, even go so far as to suggest that the earliest Americans came from Europe, not Asia, pointing to similarities between Clovis spear points and blades from France and Spain dating to between 20,500 and 17,000 years B.P. (Meltzer, Goebel and another colleague recently published a paper calling this an "outrageous hypothesis," but Dillehay thinks it's possible.)
All this speculation is spurring a new burst of scholarship about locations all over the Americas. The Topper site in South Carolina, Cactus Hill in Virginia, Pennsylvania's Meadowcroft, the Taima-Taima waterhole in Venezuela and several rock shelters in Brazil all seem to be pre-Clovis. Dillehay has found several sites in Peru that date to between 10,000 and 11,000 years B.P. but have no apparent links to the Clovis culture. "They show a great deal of diversity," he says, "suggesting different early sources of cultural development in the highlands and along the coast."
It's only by studying those sites in detail and continuing to search for more evidence on land and offshore that these questions can be fully answered. And as always, the most valuable evidence will be the earthly remains of the ancient people themselves. In one 10-day session, Kennewick Man has added immeasurably to anthropologists' store of knowledge, and the next round of study is already under way. If scientists treat those bones with respect and Native American groups acknowledge the importance of unlocking their secrets, the mystery of how and when the New World was populated may finally be laid to rest.
— With reporting by Dan Cray / Los Angeles