Debates rage among anthropologists over the details of how people came to populate the New World. How many times was the frigid Bering Strait crossed, which ethnic groups took the perilous journey, when did the migrations take place? Now an analysis of tens of thousands of skull measurements provides some new data to stew over. The study suggests that there were two migrations to the New World, the second of which consisted of people who were ethnically Asian.
Anthropologists have long suspected that humans migrated to the New World more than once, but proving this hypothesis has been extraordinarily tough. Linguistic studies provide some support. Genetic and archaeological studies, on the other hand, have been equivocal. And researchers also aren't sure just who migrated: Conventional wisdom holds that Native Americans are descended from East Asians, while recent genetic work hints at more Central Asian roots.
Now an analysis of 2000 skulls ranging from 100 to 10,000 years old adds data to the controversy. Anthropologist C. Loring Brace of the University of Michigan, Ann Arbor, and colleagues measured 21 characteristics such as nose height and head width. People in the same ethnic group exhibited similar features whereas samples from different ethnic groups differed. The measurements, coupled with archaeological data, suggest that humans migrated into the New World twice, with the first group entering 17,000 years ago, the team reports in the 31 July online edition of the Proceedings of the National Academy of Sciences. This group, from which most Native Americans are descended, seems to be most closely related to two non-Asiatic Japanese indigenous populations. A second group of migrants that is descended from Asians crossed the Bering Strait just 1000 years ago, giving rise to the Inuits and the Athabascans, groups indigenous to North America's polar region.
Anthropologist Richard Jantz of the University of Tennessee, Knoxville, says that the study makes a "rigorous" contribution to the question of how New World populations originated. But some scientists say the study's conclusions are not well supported. Geneticist D. Andrew Merriwether of the University of Michigan, Ann Arbor, says that the researchers' statistics are flimsy and that they are being fooled by skulls that look the same but are not related. "I wouldn't put much of anything in the [population] trees," he says.