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New branch of ancient humans discovered

ThaChozenWun
ThaChozenWun Members Posts: 9,390
edited December 2010 in The Social Lounge
A bone that was recently discovered in Siberia belongs to a group of humans that were neither like us or neanderthals.
A finger bone from Siberia now reveals a previously unknown group of ancient humans once existed there, one neither like us nor Neanderthals.

Bizarrely, the DNA from these extinct Siberians seems unusually similar to that of Pacific Islanders from tropical Melanesia.

The 30,000-year-old fossil was found in Denisova Cave in southern Siberia in 2008, a bone fragment that likely came from a fingertip of a young girl. [Image of finger fragment] It was discovered along with microblades (small stone blades used as tools), body ornaments of polished stone, and a molar shaped very differently from that of Neanderthals and modern humans, resembling that of much older human species, such as 🤬 habilis and 🤬 erectus. (The tooth and the finger bone apparently came from different members of the same population.)

After an international team of researchers sequenced the DNA from 40 milligrams of bone they removed from the fossil, they found the "Denisovan" (deh-NEESE-so-van) shared a common origin with Neanderthals but was genetically distinct, apparently descending from the same ancestral population of Neanderthals that had separated earlier from the ancestors of modern humans.

"It amazed me that we found this other extinct group of humans," evolutionary geneticist Svante Pääbo at the Max Planck Institute for Evolutionary Anthropology at Leipzig, Germany, told LiveScience. "When we got this little finger bone from Siberia, I was totally expecting it to be either Neanderthal or modern human. When it was something else, that was totally surprising and shocking to me."

More interbreeding

Surprisingly, their analysis found that genetic material from this sister group of Neanderthals matched 4 to 6 percent of the genomes of some modern Melanesian populations. This suggests interbreeding took place between Denisovans and the ancestors of Melanesians, just as Neanderthals appear to have interbred with the ancestors of all modern-day non-Africans.

"Instead of the clean story we used to have of modern humans migrating out of Africa and replacing Neanderthals, we now see these very intertwined story lines with more players and more interactions than we knew of before," said researcher Richard Green of the University of California, Santa Cruz.

The fact that this extinct branch of the human family tree was discovered in Siberia but contributed gene sequences to modern humans in Southeast Asia suggests it might have been widespread in Asia during the late Stone Age, said researcher David 🤬 , the evolutionary geneticist at Harvard Medical School who led the new population genetic analysis.

It remains uncertain whether this genetic material might have persisted in Melanesians because it provided an evolutionary edge of some sort. "We have a hard enough time learning what effects gene sequences might have when it comes to the genomes of modern humans, such as disease susceptibility - to do that with an archaic group is even harder," 🤬 told LiveScience.

When we met the Denisovans

These findings are adding to the complex picture of the evolutionary history of modern humans and our extinct relatives that has recently emerged, one where interbreeding has left its legacy in our DNA.

The researchers suggest an ancestral group left Africa between 300,000 and 400,000 years ago and quickly diverged, with one branch becoming the Neanderthals who spread into Europe and the other branch moving east and becoming Denisovans. When modern humans left Africa roughly 70,000 to 80,000 years ago, they first encountered the Neanderthals, with remnants of their DNA making up 1 to 4 percent of the genomes of all non-Africans. Another group of modern humans later came in contact with Denisovans.

"This study fills in some of the details, but we would like to know much more about the Denisovans and their interactions with human populations," Green said. "And you have to wonder if there were other populations that remain to be discovered. Is there a fourth player in this story?"

The researchers studiously avoid calling the Denisovans a new species or subspecies. In fact, it remains highly contentious as to whether the Neanderthals were another species altogether or were a subspecies of our species. A species is a group different enough from other groups as to be considered separate, and whose members can and do interbreed - although research has recently shown that Neanderthals (and now Denisovans) shared genes with us, so it remains an open question as to how different they were. Neanderthals and Denisovans are both called humans, however, just as all members of the genus 🤬 are - the controversy is over whether they should be lumped together with us anatomically modern humans or not.

Future research can investigate whether the Denisovan or Neanderthal remnants seen in modern humans provide any evolutionary advantages, 🤬 added.

"Maybe this is the future - reconstructing extinct relatives based not on what stone tools they made, but on their whole genomes from only little pieces of bone," Pääbo said.

The scientists detailed their findings in the Dec. 23 issue of the journal Nature.

Comments

  • ThaChozenWun
    ThaChozenWun Members Posts: 9,390
    edited December 2010
    Here's another article about the life of those people.
    NEW YORK – Scientists have recovered the DNA code of a human relative recently discovered in Siberia, and it delivered a surprise: This relative roamed far from the cave that holds its only known remains.

    By comparing the DNA to that of modern populations, scientists found evidence that these "Denisovans" from more than 30,000 years ago ranged all across Asia. They apparently interbred with the ancestors of people now living in Melanesia, a group of islands northeast of Australia.

    There's no sign that Denisovans mingled with the ancestors of people now living in Eurasia, which made the connection between Siberia and distant Melanesia quite a shock.

    It's the second report in recent months of using a new tool, genomes of ancient human relatives, to illuminate the evolutionary history of humankind. In May, some of the same scientists reported using the Neanderthal genome to show that Neanderthals interbred with ancestors of today's non-African populations. That might have happened in the Middle East after the ancestors left Africa but before they entered Eurasia, researchers said.

    As for the Denisovans, the new work is probably just the start of what can be learned from their genome, said one expert familiar with the research. Eventually, it should provide clues to traits like eye and skin color, said Todd Disotell of New York University.

    "We're going to be able to piece these people together in the next few years from this genome," he said.

    The existence of a new human relative was first revealed just nine months ago from a sampling of DNA recovered from a finger bone discovered in the Denisova Cave in southern Siberia. Researchers proposed the informal name Denisovans for them in Thursday's issue of the journal Nature, where they report the new results.

    There's not enough evidence to determine whether Denisovans are a distinct species, the researchers said.

    The genome, recovered from the finger bone, showed that Denisovans are more closely related to Neanderthals than to modern humans. That indicates that both they and Neanderthals sprang from a common ancestor on a different branch of the evolutionary family tree than the one leading to modern humans.

    Scientists have no idea what Denisovans looked like, said David 🤬 , a Harvard University researcher and an author of the new paper.

    Apart from the genome, the researchers reported finding a Denisovan upper molar in the cave. Its large size and features differ from teeth of Neanderthals or early modern humans, both of which lived in the same area at about the same time as the Denisovans.

    Neither the finger bone nor the tooth can be dated directly, but tests of animal bones found nearby show the Denisovan remains are at least 30,000 years old, and maybe more than 50,000 years old, 🤬 said.

    Scientists found evidence that in the genomes of people now living in Melanesia, about 5 percent of their DNA can be traced to Denisovans, a sign of ancient interbreeding that took researchers by surprise.

    "We thought it was a mistake when we first saw it," 🤬 said. "But it's real."

    And that suggests Denisovans once ranged widely across Asia, he said. Somehow, they or their ancestors had to encounter anatomically modern humans who started leaving Africa some 55,000 years ago and reached New Guinea by some 45,000 years ago.

    It seems implausible that this journey took a detour through southern Siberia without leaving a genetic legacy in other Eurasian populations, 🤬 said. It makes more sense that this encounter happened much farther south, indicating Denisovans ranged throughout Asia, over thousands of miles and different climate zones, he said.

    Yet, archaeologists have reported virtually no sign of the Denisovans, no tools or other indications of how they lived. Maybe that's because sites in Asia haven't been studied as systematically as Neanderthal sites in Europe, he said.

    Disotell said he and colleagues were "blown away" by the unexpected Melanesia finding, with its implication for where Denisovans lived.

    "Clearly they had to have been very widespread in Asia," and DNA sampling of isolated Asian populations might turn up more of their genetic legacy, he said.

    Rick Potts, director of the human origins program at the Smithsonian Institution, said the new work greatly strengthens the case that Denisovans differed from Neanderthals and modern humans.

    Still, they may not be a new species, because they might represent a creature already known from fossils but which didn't leave any DNA to compare, such as a late-surviving 🤬 heidelbergensis, he said.

    Potts also said the Melanesia finding could mean that the Melanesians and the Denisovans didn't intermix, but simply happened to retain ancestral DNA sequences that had been lost in other populations sampled in the study. But he stressed he doesn't know if that's a better explanation than the one offered by the authors.

    "I am excited about this paper (because) it just throws so much out there for contemplation that is testable," Potts said. "And that's good science."