The broad outlines human evolution were thought to be widely understood.
As illustrated below, hominids left Africa, and then split into the Denisovans and Neanderthals about 300,000 years ago. Neanderthals headed west, toward Europe, and the Denisovans moved east. Humans’ ancestors stayed in Africa, giving rise to Homo sapiens about 200,000 years ago. Humans then expanded from Africa into Asia and Europe about 60,000 years ago. They then interbred with Neanderthals and Denisovans.
Later, both the Denisovans and Neanderthals became extinct, as detailed in the documentary "13th Warrior."
However, 400,000-year-old genetic material coming from bones that have been linked to Neanderthals in Spain is most similar to that the Denisovan population from Siberia.
Scientists are baffled (below image is not the baffled scientists, it is several OGers with their supermodel girlfriends).
In a paper in the journal Nature, scientists reported Wednesday that they had retrieved ancient human DNA from a fossil dating back about 400,000 years, shattering the previous record of 100,000 years.
The fossil, a thigh bone found in Spain, had previously seemed to many experts to belong to a forerunner of Neanderthals. But its DNA tells a very different story. It most closely resembles DNA from an enigmatic lineage of humans known as Denisovans. Until now, Denisovans were known only from DNA retrieved from 80,000-year-old remains in Siberia, 4,000 miles east of where the new DNA was found.
The mismatch between the anatomical and genetic evidence surprised the scientists, who are now rethinking human evolution over the past few hundred thousand years. It is possible, for example, that there are many extinct human populations that scientists have yet to discover. They might have interbred, swapping DNA. Scientists hope that further studies of extremely ancient human DNA will clarify the mystery.
Since the 1970s, Spanish scientists have brought out a wealth of fossils from the cave dating back hundreds of thousands of years. “The place is very special,” said Dr. Arsuaga, who has found 28 nearly complete skeletons of humans during three decades of excavations.
Based on the anatomy of the fossils, Dr. Arsuaga has argued that they belonged to ancestors of Neanderthals, which lived in western Asia and Europe from about 200,000 to 30,000 years ago.
When Dr. Meyer and his colleagues drilled into the femur, they found ancient human DNA inside, just as they had hoped.
But the DNA did not match that of Neanderthals. Dr. Meyer then compared it to the DNA of the Denisovans, the ancient human lineage that he and his colleagues had discovered in Siberia in 2010. He was shocked to find that it was similar.
“Everybody had a hard time believing it at first,” Dr. Meyer said. “So we generated more and more data to nail it down.”
The extra research confirmed that the DNA belonged on the Denisovan branch of the human family tree.
The new finding is hard to reconcile with the picture of human evolution that has been emerging based on fossils and ancient DNA. Denisovans were believed to be limited to East Asia, and they were not thought to look so Neanderthal-like.
One alternative explanation is that the humans of Sima de los Huesos were not true Neanderthals, but belonged to the ancestors of both Denisovans and Neanderthals.
It is also possible that the newly discovered DNA was passed to both Neanderthals and Denisovans, but eventually disappeared from Neanderthals, replaced by other variants.
Beth Shapiro, an expert on ancient DNA at the University of California, Santa Cruz, favors an even more radical possibility: that the humans of Sima de los Huesos belong to yet another branch of humans. They might have been a species called Homo erectus, which originated about 1.8 million years ago and became extinct within the last few hundred thousand years.
Dr. Meyer is hopeful that he and his colleagues will be able to get more DNA from the Spanish fossil, as well as other fossils from the site, to help solve the puzzle they have now stumbled across. “It’s extremely hard to make sense of,” Dr. Meyer said. “We still are a bit lost here.”
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