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GENETIC data has backed up archaeological evidence for a relatively recent date for the arrival of humans in the Americas.

Experts disagree over when humans reached the continent. Some evidence based on mitochondrial DNA suggests an early migration 30,000 to 40,000 years ago. But physical evidence for human occupation is shaky before about 13,000 years ago (Â鶹´«Ã½, 6 September, p 17).

Now a team led by Mark Seielstad at the Harvard School of Public Health in Boston, Massachusetts, has identified a mutation on the Y chromosome known to have occurred when people were still living…