Retrieved Genes Hint At Neanderthals' End

Did modern humans wipe out the Neanderthal people who inhabited Europe until 28,000 years ago or did the two populations merge through interbreeding? New DNA evidence extracted from the ribs of a Neanderthal infant, one of the last of its kind, supports the thesis that these hardy, beetle-browed people left little or no genetic legacy in today's populations.

Even though Neanderthals perished long ago, the surprising retrieval of intact DNA, the second such sample to be recovered, has set biologists speculating that with further finds the genetics of this extinct human species could become quite well understood.

The two DNA retrievals, both suggesting that Neanderthals were a separate human species, come before and after a startlingly contradictory finding made last June. After studying the remains of a boy recovered in Portugal paleoanthropologists said the human child had strong Neanderthal features, suggesting, they said, that modern humans had interbred with Neanderthals. Neanderthals and their forebears occupied modern Europe from around 300,000 years ago. They were adapted to the cold conditions of the ice age and had stocky bodies, thick bones and enormous strength. Though their stone tools seem similar to those of modern humans who started to enter Europe from Asia around 35,000 years ago, they ceased to flourish and abruptly disappeared throughout their home range around 28,000 years ago, leaving no clues in the archaeological record as to the reason for their extinction.

Neanderthal DNA was first isolated three years ago from the original bones first found in the Feldhofer Cave in the Neander Valley near D?sseldorf in 1856. The finding was startling because no human DNA of such antiquity - at least 30,000 years old - had been recovered and because it showed a pattern of DNA that was quite different from that of modern humans.

Though the Feldhofer DNA was extracted with elaborate precautions, the finding was greeted with some reservation because it was a single result. Confirmation has now come from a second Neanderthal.

The remains were recovered by a Russian expedition from the Moscow Institute of Archaeology to the Mezmaiskaya Cave in the Caucasus, to the northeast of the Black Sea. They belonged to a Neanderthal infant less than 2 months old, too young for the sex to be determined from the bones. The bones were dated by the carbon isotope method to 29,000 years ago, making the infant among the last generations of the Neanderthals.

A sample of the infant's ribs was made available by the Russian researchers to Dr. William Goodwin of the Human Identification Center at the University of Glasgow in Scotland.

Goodwin and Russian and Swedish colleagues report in this week's issue of Nature that the DNA sequence from the Mezmaiskaya Cave is 3.5 percent different from that of the Feldhofer Cave Neanderthal, suggesting a considerable genetic diversity within the Neanderthal population.

But the two Neanderthal DNA sequences are very different from those of modern humans, Goodwin and his colleagues say. Based on the rate at which DNA changes over time in living organisms, Goodwin calculated that the two Neanderthals last shared a common ancestor at least 150,000 years ago, a date that matches the first fully Neanderthal remains, and that the Neanderthal and modern human lineages split some 600,000 years ago.