Humans and Neanderthals

This file figure dated 10 August 2006 shows the figure of a Neanderthal man standing at the entrance hall of the Neanderthals museum in Mettmann, Germany. Recently an important genotype of the Neanderthal man was deciphered at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. (EPA/HORST OSSINGER)

Houston Chronicle

Nov. 16, 2006, 5:41AM

Humans, Neanderthals closer on family tree

But it's the differences in DNA that excite scientists most

By ERIC BERGER

Scientists peering into the hazy history of modern humans and their more brutish cousins, the Neanderthals, say they have discovered the two species are almost identical.

Between 500,000 and 700,000 years ago the two lineages split but continued to interbreed, slowly drifting apart genetically, scientists say. About 370,000 years ago the mixing stopped and the family tree split irrevocably, with one branch leading to Neanderthals and the other to humans, researchers say.

Scientists reached this conclusion, reported in this week's editions of Nature and Science magazines, after cobbling together 1.1 million DNA letters of the Neanderthal genome.

Though less than 1 percent of the complete genetic code, it's enough of a glimpse to begin drawing meaningful conclusions, the researchers contend.

The research teams used DNA extracted from a 38,000-year-old Neanderthal found in Vindija, Croatia. But decoding a Neanderthal genome isn't as simple as taking a sample of human blood and feeding bits of DNA into sequencing machines.

About 95 percent of the DNA in the sample belonged to bacteria and other microbes, which had feasted on nutrients within the bone. So the scientists sequenced all the DNA and plucked only the samples that closely resembled human DNA.

The leaders of the two science teams researching Neanderthal DNA, Svante Paabo of the Max Planck Institute in Germany and Edward Rubin of the Lawrence Berkeley National Laboratory in Berkeley, Calif., said they expected to deliver a rough draft of a Neanderthal genome within two years.

"Clearly we're at the dawn of Neanderthal genomics," Rubin said during a teleconference with reporters. "There's no question we're going to have a Neanderthal genome."

That's significant because Neanderthals, who became extinct about 28,000 years ago and lived among humans in Asia and Europe, are humanity's closest cousin. Rubin and Paabo estimate that when the entire Neanderthal sequence is complete, it will be 99.5 to 99.9 percent the same as the human genome, and the two species will share a large majority of the same 25,000 genes.

But not all — and that is the prospect that most excites scientists.

"Their genes are going to be pretty darn close to ours," said John Hawks, an anthropologist at the University of Wisconsin in Madison. "But we will find differences, and that will give us insight into what it means to be human."

Until now, scientists have culled through the genetic differences between humans and chimpanzees to find the genes that make humans unique. Chimpanzees share about 98.5 percent of their DNA with humans, making them the closest living relative. But the last common ancestor between humans and chimpanzees lived 6.5 million years ago.

By comparing the Neanderthal genome to that of chimpanzees, scientists say they will have an unparalleled opportunity to find the genes, such as those related to more developed brains and tool-making skills unique to humans.

The new research also sheds new light on the mysterious Neanderthals themselves, who many scientists think were somehow wiped out by humans.

Hawks compared the past research of Neanderthals — consisting primarily of scientists studying a few skeletons — to peering at distant planets through telescopes.

"With Neanderthals, we're always looking at them through a great distance, and there's only been these fragments left behind," Hawks said. "Suddenly, we have this enormous set of data that anyone with a computer can look at."

Anthropologists know that Neanderthals used stone tools, but their spears required close-in contact with game.

By contrast, human spears could be flung across longer distances. Neanderthals also developed and matured faster than humans, and were more hardy and capable of surviving harsher, colder climates. The genes may explain why.

But little is known of their demise: Did they lose to humans in competition for game? Was their genetic make-up such that they could not handle the diseases carried by humans?

Already the genetic evidence appears to have dispelled one of the previously leading theories: that extensive interbreeding between earlier humans and Neanderthals resulted in a single species, modern man.

The new studies confirm earlier suggestions that any interbreeding was fleeting, at best, because of such a distant divergence in the two species.

Scientists hailed the new research because it represents a "stunning success" in studying ancient DNA.

eric.berger@chron.com