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Six years ago, D. Andrew Merriwether was a master's student in the lab of geneticist Douglas Wallace at Emory University in Atlanta, learning to use genes to trace the ancestry of native American peoples. When he left to pursue doctoral studies at the University of Pittsburgh, Merriwether continued that research, expecting to bolster the conclusion coming from the Wallace lab: that genetically distinct groups of prehistoric people migrated to the Americas in three separate waves. But this year, Merriwether found himself publicly contradicting his mentor, in a series of papers suggesting that there was only a single migration. Although they remain personally friendly, mentor and student clearly are divided on this issue. Says Merriwether, now at the University of Michigan: "I feel badly about it because Wallace is the one who inspired me to go into this field. It's awkward."
Chalk up one more disagreement to one of the most contentious issues in human prehistory: the question of who settled the Americas. A decade ago, intellectual battles raged over a bold synthesis of linguistic, genetic, and dental data named after co-creator Joseph Greenberg, a Stanford University linguist. The Greenberg theory suggested that the first Americans arrived from Asia in at least three separate waves, each wave giving rise to one of three linguistic groups. Linguists opposed putting the diverse languages of most native Americans into one "Amerind" group, but the theory fit dental and genetic evidence from several labs, including Wallace's.
But now the pillar of support from genetics is showing cracks, thanks to new data from Merriwether and others, including a European team whose review is published in the October issue of the American Journal of Human Genetics. Additional DNA samples and better resolution show that native Americans as diverse as the Eskimos of Alaska and the Kraho and Yanomami of Brazil share more gene types than previously thought, which suggests that they are descended from the same founding populations in Asia-and that their ancestors entered North America in only one or two migratory waves, says Oxford University evolutionary geneticist Ryk Ward. Scientists are already searching for those ancestors' closest kin in Siberia and Mongolia.
Not surprisingly, not everyone supports the new interpretations. Greenberg, for example, says that given the flip-flopping conclusions from the...