What Happened to the Neanderthals? Check Their DNA

Article excerpt

Humans' closest cousins, the Neanderthals, vanished 30,000 years ago after sharing turf with humans for millenniums. But why they disappeared remains a mystery.

Two research teams decided to try a new approach: Instead of studying tiny fragments of DNA from one of these cousins, they looked for ways to string fragments together to get a more complete source of potential genetic clues. Conventional wisdom held that this task was impossible for material this old. But using the 38,000- year-old remains of a 38-year-old male, found in a Croatian cave, each group now says it has rebuilt, or sequenced, long segments of Neanderthal DNA - the twisted, ladder-shaped molecule in the nucleus of cells that holds an organism's genetic blueprint.

The technique is not only yielding new insights into Neanderthals, reported in Thursday's issue of the journal Nature and Friday's issue of Science, it's also likely to prove an important tool in teasing out secrets about how plants and animals evolved, researchers say. DNA "is the ultimate forensic record of evolution," says Sean Carroll, an evolutionary biologist at the University of Wisconsin-Madison. "There's never been a more exciting time to be an evolutionary biologist."

Within the next two years, one team hopes to finish a rough draft of the Neanderthal's full genome. This would help scientists answer nagging questions about the Neanderthals' evolutionary history, including factors contributing to their demise. It also would yield insights into the evolutionary history of modern humans.

"We are at the dawn of Neanderthal genomics," says Dr. Rubin, with the US Department of Energy's Joint Genome Institute in Walnut Creek, Calif. He likens the effort to those of archaeologists who deciphered hieroglyphics to learn about ancient Egyptians in detail.

The results that will be published this week are "really a big teaser," says Anne Stone, who heads the Molecular Anthropology Laboratory at Arizona State University. But it's an important one, she adds. The sequences the two teams have produced cover 65,000 to 1 million base pairs. Each base pair is built from four basic chemicals that make up an organism's genetic "code." Each base pair forms a "rung" on the DNA molecule's ladder. By comparison, the human genome, and presumably the Neanderthal's, consists of some 3 billion base pairs. But the DNA strands that the teams have strung together are far longer than any previous length of Neanderthal DNA.

The samples are based on DNA in the cell nucleus. This DNA carries contributions from a father and a mother. …