Neanderthal DNA: No Human Hanky-Panky

Nov. 15, 2006 — Early humans and Neanderthals, our closest and ill-fated evolutionary cousins, shared the same habitat for hundreds of thousands of years, but engaged in little or no inter-species hanky-panky, scientists have said.

Two pathbreaking studies published Wednesday in the journals Nature and Science also confirmed earlier estimates that the two related branches of the hominid family tree went their separate genetic ways some 500,000 years ago.

Using distinct techniques of DNA sequencing — which analyzes genetic fragments recovered, in this case, from Neanderthal remains — the coordinated scientific papers also predicted that the complete Neanderthal genome would be pieced together within two years.

Not long ago the prospect of sequencing the entire genome of an extinct organism was regarded by many specialists as simply impossible.

The demise of Neanderthals some 30,000 years ago is often blamed on smarter and more adaptable Homo sapiens, but there is still no scientific consensus on the exact cause of extinction.

The two studies, one headed by Edward M. Rubins and the other by Svante Paabo, arrived at similar conclusions using cutting-edge but different scientific tools.

A commentary in Nature introducing both papers suggested they were the "most significant contributions" published in the field since the discovery of Neanderthals 150 years ago.

The team of U.S., German and Croat researchers led by Paabo, Director of the Genetics Department at the Max Planck Institute for Evolutionary Anthropology in Leipzig, used a technique called pyrosequencing to analyze one million base pairs of Neanderthal DNA, removing impurities and matching the fragmentary genetic sequences against the template of human chromosomes.

"Our finding that the Neanderthal and human genomes are at least 99.5 percent identical led us to develop and successfully implement a targeted method for recovering specific ancient DNA sequences," the authors wrote.

The human genome contains some 3.2 billion chemical nucleotide bases, grouped within some 30,000 genes.

The Nature paper concluded that human and Neanderthal DNA diverged between 465,000 and 569,000 years ago, and that Neanderthals, like humans, "derived from a very small ancestral population of about 3,000 individuals."

Rubin's study, published in the journal Science, used what is called a "metagenomic" technique to sequence some 65,000 base pairs of Neanderthal DNA which are amplified through replication in bacteria. The result is then further amplified using enzymes.

Rubin works at the Lawrence Berkeley National Laboratory in Berkeley, Calif., and is director of the Department of Energy's Joint Genome Institute in Walnut Creek, also in California.

His analysis yielded a similar, albeit wider, estimate of when Homo sapiens and Neanderthals took different evolutionary paths: between 120,000 and 670,000 years ago.

The more we learn about the hominids who didn't cut the evolutionary grade, the scientists concluded, the more we learn about ourselves.

"The full Neanderthal genome," they added, will also help resolve a long-standing debate: "In evolution, how important are mutations in genes that result in structural and physiological changes, compared with mutations that affect the regulation of those genes?"

The first evidence for the Neanderthals emerged in 1856, when workers at a lime quarry in the Neander Valley, western Germany, came across bones initially thought to be that of a bear.

Since then, the remains of about 400 Neanderthals have been found, at sites ranging from southern England to continental Europe and the Middle East.