After years of spirited debate over how and when people first reached the Americas, scientists finally seem poised to reach agreement. The emerging consensus: In contrast to what was long held as conventional wisdom, it now seems likely that the first Americans did not wait for ice sheets covering Canada to melt some 13,000 years ago, which would have allowed them to traipse south over solid ground. Instead, early nomads might well have traveled by boat or at least along the coast from Siberia to North America, perhaps navigating arctic waters near today's Bering Strait. The telltale evidence: ancient DNA from those early people that's been coaxed, by powerful analytical technology, into revealing its secret.

Rewriting the prehistory of the Americas is perhaps the most remarkable discovery—but hardly the only one—so far achieved through the analysis of ancient DNA. Other new insights about the past are being drawn from the same emerging scientific discipline. In the past five years, the double helix has shed light, for example, on the vanished woolly mammoth, the flightless dodo, and even humanity's long-lost kin, the Neanderthals. Extracting and testing old DNA, once considered practically impossible because too little of the stuff survives the eons intact, are now at the cutting edge of archaeology, paleontology, and other fields, thanks to new techniques and more powerful technology.