Neanderthals Died Out Earlier Than Thought

Neanderthals may have died out earlier than before thought, researchers say.

These findings hint that Neanderthals did not coexist with modern humans as long as previously suggested, investigators added.

Modern humans once shared the planet with now-departed human lineages, including the Neanderthals, our closest known extinct relatives. However, there has been heated debate over just how much time and interaction, or interbreeding, Neanderthals had with modern humans.

To help solve the mystery, an international team of researchers investigated 215 bones previously excavated from 11 sites in southern Iberia, in an area known as Spain today. Neanderthals entered Europe before modern humans did, and prior research had suggested the last of the Neanderthals held out in southern Iberia until about 35,000 years ago, potentially sharing the region with modern humans for thousands of years.

Their data suggest that modern humans and Neanderthals may have actually lived in the area at completely different times, never crossing paths there at all. Even so, these findings do not call into question whether modern humans and Neanderthals once had sex - the findings simply indicate this interbreeding must have occurred earlier, before modern humans entered Europe.

"The genetic evidence for interbreeding - 1 to 4 percent Neanderthal DNA in present-day modern humans - suggests that interbreeding probably occurred before the period we are looking at in the Levant, the region around Israel and Syria, when modern humans first migrated out of Africa," researcher Rachel Wood, an archaeologist and radiocarbon specialist at Australian National University in Canberra, told LiveScience.

Dating bones Scientists discover the ages of artifacts and fossils using a variety of techniques. For instance, radiocarbon dating determines the age of biological remains based on the ratio between the carbon isotopes (atoms of the same element with different numbers of neutrons) carbon-12 and carbon-14 it holds - this proportion changes as radioactive carbon-14 breaks down while stable carbon-12 does not. Researchers can also look at the layers of soil and rock in which objects are found - if these layers were not disturbed over the years, then objects in the same layer should be the same age.

The investigators concentrated on collagen, the part of bone most suited for radiocarbon dating. Only eight of these bones from two sites in Spain - Zafarraya Cave and Jarama VI - had enough collagen for analysis. (Image Gallery: Our Closest Human Ancestor)

One bone, which came from a wild goat, was found in Zafarraya Cave in a similar layer as Neanderthal fossils. The bone was previously estimated as 33,300 years in age. However, using an ultrafiltration technique that cleansed the bone of modern carbon impurities that can give inaccurate younger dates, they found the bone was more than 46,700 years old.

"Our work suggests that at present, it is unlikely that Neanderthals survived any later in this area than they did elsewhere in mainland Europe," said researcher Thomas Higham at the University of Oxford in England.

The most surprising thing "was the enormous difference that the ultrafiltration dating made to the chronologies of the sites we looked at," Wood said. "At other sites in Europe, we have seen that this improved method of dating bone makes a difference, making old bones older. However, we do not normally see such consistently large differences. This is probably because the preservation of the organic materials - bone and charcoal - that are normally radiocarbon dated is really poor in warm climates like southern Spain."

Analysis of the remaining samples revealed they were at least 10,000 years older than previously estimated. Instead, they were close to or more than 50,000 years old, the upper limit for radiocarbon dating.

When Neanderthals died out "Our results cast doubt on a hypothesis that has been broadly accepted since the early 1990s - that the last place for surviving Neanderthals was in the southern Iberian Peninsula," Wood said. "Much of the evidence that has supported this idea is based on a series of radiocarbon dates, which cluster at around 35,000 years ago. Our results call all of these results into question."

These findings suggest modern humans and Neanderthals might not have interacted in this area. In northern Iberia, about 150 miles (250 kilometers) north of Jarama VI, past research suggested modern humans were only present starting about 42,000 years ago. These new findings hint that modern humans and Neanderthals did not coexist for millennia as before thought, and did not live side-by-side. (10 Mysteries of the First Humans)

"The results of our study suggest that there are major problems with the dating of the last Neanderthals in modern-day Spain," Higham said. "We now have to look very cautiously at the model of late Neanderthal survival in southern Iberia and focus our efforts on more rigorous dating programs."

One site, Cueva Antón in Spain, did seem as young as previously thought. However, it remains uncertain whether the artifacts there are linked with Neanderthals - they may belong to modern humans.

The researchers caution they are not definitely saying that there were no Neanderthals in southern Iberia after 42,000 years ago. "What we have is a gap where we have no reliable radiocarbon dates. There might have been Neanderthals or modern humans or both or neither," Wood said. Also, "there are several circumstances which could have obscured later interbreeding events in Europe, so it is not possible to say, for example, that at one time there was not more Neanderthal DNA in Europeans."

The scientists detailed their findings online Feb. 4 in the journal Proceedings of the National Academy of Sciences.

This article originally appeared on LiveScience.com.

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The last Neanderthals had passed by southern Iberia quite earlier than previously thought.

Back in the Beginning

To put a human face on our ancestors, scientists from the Senckenberg Research Institute used sophisticated methods to form 27 model heads based on tiny bone fragments, teeth and skulls collected from across the globe. The heads are on display for the first time together at the Senckenberg Natural History Museum in Frankfurt, Germany. This model is Sahelanthropus tchadensis, also nicknamed "Toumai," who lived 6.8 million years ago. Parts of its jaw bone and teeth were found nine years ago in the Djurab desert in Chad. It's one of the oldest hominid specimens ever found.

Australopithecus afarensis

With each new discovery, paleoanthropologists have to rewrite the origins of man's ancestors, adding on new branches and tracking when species split. This model was fashioned from pieces of a skull and jaw found among the remains of 17 pre-humans (nine adults, three adolescents and five children) which were discovered in the Afar Region of Ethiopia in 1975. The ape-man species, Australopithecus afarensis, is believed to have lived 3.2 million years ago. Several more bones from this species have been found in Ethiopia, including the famed "Lucy," a nearly complete A. afarensis skeleton found in Hadar.

Australopithecus africanus

Meet "Mrs. Ples," the popular nickname for the most complete skull of an Australopithecus africanus, unearthed in Sterkfontein, South Africa in 1947. It is believed she lived 2.5 million years ago (although the sex of the fossil is not entirely certain). Crystals found on her skull suggest that she died after falling into a chalk pit, which was later filled with sediment. A. africanus has long puzzled scientists because of its massive jaws and teeth, but they now believe the species' skull design was optimal for cracking nuts and seeds.

Paranthropus aethiopicus

The skull of this male adult was found on the western shore of Lake Turkana in Kenya in 1985. The shape of the mouth indicates that he had a strong bite and could chew plants. He is believed to have lived in 2.5 million years ago and is classified as Paranthropus aethiopicus. Much is still unknown about this species because so few reamins of P. aethiopicus have been found.

Paranthropus boisei

Researchers shaped this skull of "Zinj," found in 1959. The adult male lived 1.8 million years ago in the Olduvai Gorge of Tanzania. His scientific name is Paranthropus boisei, though he was originally called Zinjanthropus boisei -- hence the nickname. First discovered by anthropologist Mary Leakey, the well-preserved cranium has a small brain cavity. He would have eaten seeds, plants and roots which he probably dug with sticks or bones.

Homo rudolfensis

This model of a sub-human species -- Homo rudolfensis -- was made from bone fragments found in Koobi Fora, Kenya, in 1972. The adult male is believed to have lived about 1.8 million years ago. He used stone tools and ate meat and plants. H. Rudolfensis' distinctive features include a flatter, broader face and broader postcanine teeth, with more complex crowns and roots. He is also recognized as having a larger cranium than his contemporaries.

Homo ergaster

The almost perfectly preserved skeleton of the "Turkana Boy" is one of the most spectacular discoveries in paleoanthropology. Judging from his anatomy, scientists believe this Homo ergaster was a tall youth about 13 to 15 years old. According to research, the boy died beside a shallow river delta, where he was covered by alluvial sediments. Comparing the shape of the skull and teeth, H. ergaster had a similiar head structure to the Asian Homo erectus.

Homo heidelbergensis

This adult male, Homo heidelbergensis, was discovered in in Sima de los Huesos, Spain in 1993. Judging by the skull and cranium, scientists believe he probably died from a massive infection that caused a facial deformation. The model, shown here, does not include the deformity. This species is believed to be an ancestor of Neanderthals, as seen in the shape of his face. "Miquelon," the nickname of "Atapuerca 5", lived about 500,000 to 350,000 years ago and fossils of this species have been found in Italy, France and Greece.

Homo neanderthalensis

The "Old Man of La Chapelle" was recreated from the skull and jaw of a Homo neanderthalensis male found near La Chapelle-aux-Saints, in France in 1908. He lived 56,000 years ago. His relatively old age, thought to be between 40 to 50 years old, indicates he was well looked after by a clan. The old man's skeleton indicates he suffered from a number of afflictions, including arthritis, and had numerous broken bones. Scientists at first did not realize the age and afflicted state of this specimen when he was first discovered. This led them to incorrectly theorize that male Neanderthals were hunched over when they walked.

Homo floresiensis

The skull and jaw of this female "hobbit" was found in Liang Bua, Flores, Indonesia, in 2003. She was about 1 meter tall (about 3'3") and lived about 18,000 years ago. The discovery of her species, Homo floresiensis, brought into question the belief that Homo sapiens was the only form of mankind for the past 30,000 years. Scientists are still debating whether Homo floresiensis was its own species, or merely a group of diseased modern humans. Evidence is mounting that these small beings were, in fact, a distinct human species.

Homo sapiens

Bones can only tell us so much. Experts often assume or make educated guesses to fill in the gaps in mankind's family tree, and to develop a sense what our ancestors may have looked like. Judging from skull and mandible fragments found in a cave in Israel in 1969, this young female Homo sapien lived between 100,000 and 90,000 years ago. Her bones indicate she was about 20 years old. Her shattered skull was found among the remains of 20 others in a shallow grave.