People first set foot in the Americas no earlier than about 18,000 years ago, according to an analysis of a newly identified gene variant on the Y chromosome.
This evidence supports the longstanding archaeological theory that New World settlers crossed a land bridge from Asia to North America about 14,000 years ago, say geneticist Mark Seielstad of the Genome Institute of Singapore and his colleagues.
The Y chromosome data generate a more precise estimate of colonization of the Americas than earlier DNA studies provided, the researchers contend. Some previous investigations–including analyses of genes in cells' mitochondria and nuclei–yielded settlement dates as early as 40,000 years ago.
"[Our] discovery . . . places the DNA evidence more in line with archaeological data," Seielstad and his coworkers conclude in the September American Journal of Human Genetics.
Their finding builds on a reconstruction of Y chromosome-based lineages worl