Were the primary ancestors of today's Native Americans really the first people to set foot in the New World? Genetic evidence suggests so, but ancient skeletons tell a different story. Now, the most detailed analysis yet of ancient American skulls concludes that there were two distinct waves of colonizers from Asia, suggesting that another group got here first.
A team of paloeanthropologists compared the skulls of several dozen Paleoamericans, which date back to the early days of migration 11,000 years ago, with those of more than 300 Amerindians, which date to 1000 years ago. The Paleoamerican remains came from four sites in South and Central America, and the researchers also compared them with more than 500 skulls from East Asia. In all, the team found clear differences in the shapes and sizes of the Paleoamerican and Amerindian samples. That suggests that more than one group of individuals migrated to the Americas from Asia, the team reports online today in PLoS ONE. And due to the age of the skeletons, the researchers say, this other group of individuals arrived before the primary ancestors of today's Native Americans.
Team member Katerina Harvati of Germany's Tübingen University says that although the study does not rule out a single migration, it demonstrates "that the story of the peopling of the New World was most likely more complex than is commonly thought."
The work is "solid" and "perhaps the most sophisticated analysis of craniofacial traits undertaken to date," says Theodore Schurr, a molecular anthropologist at the University of Pennsylvania. Schurr's own recent work on DNA in living people has led him to favor a single migration, but he says he is "willing to accept that there were pulses of migration into the Americas from Northeast Asia at different times."
Nevertheless, Schurr warns that the lack of large numbers of Paleoamerican skulls makes progress difficult and that the small sample sizes may not show the true morphological and genetic diversity of early American populations. The field, he notes, continues to be hampered by the lack of ancient DNA data because of poor bone preservation. Genetic studies of modern populations, by contrast, can draw on large numbers of samples. Dennis Stanford, an archaeologist at the Smithsonian Institution in Washington, D.C., adds that the authors could have benefited from additional samples from North America as well as more Asian skulls. He believes that there likely were three or four major migrations.
Harvati hopes that further studies will include more samples and agrees that "ancient DNA would be extremely helpful." But so far, she notes, such studies have not had much success.