Neanderthals might have held out in isolated refuges for thousands of years longer than previously thought, scientists reported today.

Their survival at what seems to have been their last refuge in Gibraltar for far longer after the arrival of modern humans than once believed suggests our ancestors may not have driven the Neanderthals to extinction. Instead, researchers speculate the Neanderthals fell victim to a cooling of the climate that deteriorated their environment too rapidly for them to adapt.

"While the rest of where they lived was getting colder, down here at the southernmost tip of Europe there were still little pockets of Mediterranean climate, so the world of the Neanderthals there didn’t change that much," researcher Clive Finlayson, an evolutionary biologist at the Gibraltar Museum, told LiveScience.

This now prolonged span of time in which modern humans and Neanderthals could have interacted reopens possibilities they might have interbred, experts added.

More like wrestlers

The researchers investigated Gorham’s Cave, where Neanderthal stone tools such as spear tips were found more than 50 years ago. Neanderthal tools differ from those of modern humans by the way the rock was chipped off and trimmed and by their very size and weight.

"Neanderthals were more like wrestlers, while modern people are in comparison more like long-distance runners," Finlayson explained. "Neanderthals made heavy spears for close quarter ambush hunting of large animals such as rhinos or elephants. Tools of modern people were lighter and perhaps more portable for people who were on the move."

By carbon-dating charcoal from hearths newly excavated at Gorham’s cave, the scientists found Neanderthals might have survived there until 28,000 years ago, and maybe as recently as 24,000 years ago.

While the rest of Europe was cooling, the area around Gibraltar back then "resembled a European Serengeti," Finlayson said. Leopards, hyenas, lynxes, wolves and bears lived amongst wild cattle, horses, deer, ibexes, oryxes and rhinos, all surrounded by olive trees and stone pines, with partridges and ducks overhead, tortoises in the underbrush and mussels, limpets and other shellfish in the waters.

This natural richness of wildlife and plants in the nearby sandy plains, woodlands, shrublands, wetlands, cliffs and coastline probably helped the Neanderthals to persist, he added. Indeed, evidence at the cave shows the Neanderthals likely used it as a shelter on and off "for 100,000 years," Finlayson said.

Changing climate

As the climate cooled, the forested and semi-forested areas Neanderthals were best adapted to were replaced in Europe by tundra from the north and steppe from the east. Modern humans, who were more mobile, might have been better suited for the open expanses of these terrains.

"The key was physique, which for Neanderthals did not change fast enough," Finlayson said.

Prior findings suggested the Neanderthals went extinct in Europe 35,000 years ago, while modern humans arrived in Western Europe some 32,000 years ago. The fact the span between the arrival of modern humans and the extinction of the Neanderthals looked so relatively brief hinted that Neanderthals got out-competed.

These new findings suggest Neanderthals survived after modern humans moved in, and as the environment changed due to climate shifts, Neanderthals faded away.

Interbreeding possible

If Neanderthals lasted longer than once thought, the question of whether Neanderthals and modern humans interbred is raised again, said paleoanthropologist Eric Delson at the American Museum of Natural History and at Lehman College in New York.

Past digs had uncovered what some researchers claimed was the skeleton of a hybrid child. "How could there be a hybrid, if the last Neanderthal died out thousands of years before this child was born? But if it can be shown that Neanderthals were still living near Gibraltar some 24,000 years ago, that part of the hesitancy disappears," Delson said. Still, he added, questions remain about whether the skeleton really does resemble a Neanderthal’s.

Future research can delve deeper into Gorham’s Cave or other nearby caves, Finlayson said. "They might be lucky enough to find some Neanderthal fossils, which would help document who made the artifacts," Delson said.

source: LiveScience

A reconstructed Neanderthal skeleton, right, and a modern human version of a skelaton, left, are on display at the Museum of Natural History Wednesday, Jan. 8, 2003 in New York. Credit: AP Photo

Humans and their close Neanderthal relatives began diverging from a common ancestor about 700,000 years ago, and the two groups split permanently some 300,000 years later, according to two of the most detailed analyses of Neanderthal DNA to date.

Using different techniques, two teams of scientists separately sequenced large chunks of DNA extracted from the femur of a 38,000-year-old Neanderthal specimen found in a cave 26 years ago in Croatia. One team sequenced more than one million base pairs and the other 65,000 pairs of the genome.

The achievements could help shed light on the evolution of our own species, and it paves the way for building a complete library of the Neanderthal genome, the scientists say.

No evidence of interbreeding

In popular imagination, Neanderthals are often portrayed as prehistoric brutes who became outsmarted by a more advanced species, humans, emerging from Africa. But excavations and anatomical studies have shown Neanderthals used tools, wore jewelery, buried their dead, cared for their sick, and possibly sang or even spoke in much the same way that we do. Even more humbling, perhaps, their brains were slightly larger than ours.

The results from the new studies confirm the Neanderthal’s humanity, and show that their genomes and ours are more than 99.5 percent identical, differing by only about 3 million bases.

"This is a drop in the bucket if you consider that the human genome is 3 billion bases," said Edward Rubin of the Lawrence Berkeley National Laboratory, who led one of the research teams.

For comparison, the genomes of chimpanzees, our closest living relatives, differ from humans by about 30 million to 50 million base pairs.

The findings also appear to refute speculations by some scientists that Neanderthals and humans interbred in more recent times. "We see no evidence of mixing 30,000 to 40,000 years ago in Europe," Rubin said. "We don’t exclude it, but from the data that we have, we have no evidence that pages were ripped from one genome and put in the other."

Ruling out contamination

One of the biggest challenges in sequencing Neanderthal DNA is finding a bone sample that hasn’t been too contaminated by human handling. Fortunately, the femur fragment used in the studies was relatively small and uninteresting, causing it to be largely overlooked.

The femur "was thrown in a big box of uninformative bones and not handled very much," said Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Germany, leader of the other sequencing project. "Whereas more interesting bones—where you can study the muscle attachment and the morphology of Neanderthals—had been extensively cleaned and handled and thus tend to be much more contaminated."

The researchers also relied on other clues, such as chemical damage unique to ancient DNA, to help verify that the genetic material was indeed Neanderthal. "One of the crucial things is that we feel confident that the DNA we have, which we’re calling Neanderthal, is truly Neanderthal," Rubin said.

New advances

The success of the two team’s sequencing projects were made possible by recent advances in DNA sequencing technology, which now allow scientists to sequence DNA over 100 times faster than in the past.

Paabo’s team recovered more than a million Neanderthal base pairs using a new automated technique called "pyrosequencing." In this process, DNA fragments are attached to tiny artificial beads, sequenced, and then matched to similar sections on human chromosomes.

Rubin’s team employed "metagenomics," which involves integrating short fragments of extracted Neanderthal DNA into the genomes of bacteria. The Neanderthal DNA gets amplified as the bacteria divide, and then scientists pluck out human-matching bases using "probes" made with snippets of human DNA.

The researchers say their achievements mark the "dawn of Neanderthal genomics," and they estimate that further advances in DNA sequencing technology could allow the completion of a very rough draft of the entire Neanderthal genome within two years.

"There’s no question that we’re going to have a Neanderthal genome, and likely, we’re going to have several Neanderthal genomes," Rubin said. The team hopes to extract and sequence DNA from the bones of other individuals and to complete several drafts of the Neanderthal genome.

Clues to our past

A complete Neanderthal genome would help scientists identify the genetic changes in our own genome that set us apart from other hominids.

The comparison between recently sequenced chimpanzee genomes and ours is already shedding light on the evolutionary changes our ancestors went through to make them less ape-like. But because chimps and humans began diverging some 6.5 million years ago, examination of their genome cannot reveal what happened in the final stretches of our own evolution.

"Humans went through several stages of evolution in the last 400,000 years," said study co-author Jonathan Pritchard of the University of Chicago. "If we can compare humans’ and Neanderthals’ genomes, then we can possibly identify what the key genetic changes were during that final stage of human evolution."

A completed genome will also reveal new insights about Neanderthals, who disappeared mysteriously about 30,000 years ago.

"In having the Neanderthal genome sequence …we’re going to learn about the biology, learn about things that we could never learn from the bones and the artifacts that we have," Rubin said.

source: LiveScience