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发帖数: 233 | 1 俄国发现远古人类遗骨
俄罗斯的研究人员说，他们发现了不曾为人所知的早期人类的遗骨。
对在西伯利亚一个山洞中发现的一个牙齿和指骨进行的DNA检测显示，这些被称为“丹尼索夫”人
（Denisovan）的早期人类生活在3万年前，尼安德特人(Neanderthal）是他们的近亲，不过并没
有足够的证据证明他们是两个不同的物种。
基因研究还证明一些“丹尼索夫”人同美拉尼西亞人（Melanesian）的祖先曾经互相交配。
http://www.bbc.co.uk/news/science-environment-12059564
Ancient humans, dubbed 'Denisovans', interbred with us
Professor Chris Stringer: "It's nothing short of sensational - we didn't
know know how ancient people in China related to these other humans"
Scientists say an entirely separate type of human identified from bones
in Siberia co-existed and interbred with our own species.
The ancient humans have been dubbed "Denisovans" after the caves in
Siberia where their remains were found.
There is also evidence that this population was widespread in Eurasia.
A study in Nature journal shows that Denisovans co-existed with
Neanderthals and interbred with our species - perhaps around 50,000
years ago.
An international group of researchers sequenced a complete genome from
one of the ancient hominins (human-like creatures), based on nuclear DNA
extracted from a finger bone.
'Sensational' find
According to the researchers, this provides confirmation there were at
least four distinct types of human in existence when anatomically modern
humans (Homo sapiens sapiens) first left their African homeland.
DNA from a tooth (pictured) and a finger bone show the Denisovans were a
distinct group
Along with modern humans, scientists knew about the Neanderthals and a
dwarf human species found on the Indonesian island of Flores nicknamed
"The Hobbit". To this list, experts must now add the Denisovans.
The implications of the finding have been described by Professor Chris
Stringer of the Natural History Museum in London as "nothing short of
sensational".
Scientists were able to analyse DNA from a tooth and from a finger bone
excavated in the Denisova cave in southern Siberia. The individuals
belong to a genetically distinct group of humans that were distantly
related to Neanderthals but even more distantly related to us.
The finding adds weight to the theory that a different kind of human
could have existed in Eurasia at the same time as our species.
Researchers have had enigmatic fossil evidence to support this view but
now they have some firm evidence from the genetic study carried out by
Professor Svante Paabo of the Max Planck Institute in Leipzig, Germany.
"A species of early human living in Europe evolved," according to
Professor Paabo.
"There was a western form that was the Neanderthal and an eastern form,
the Denisovans."
The study shows that Denisovans interbred with the ancestors of the
present day people of the Melanesian region north and north-east of
Australia. Melanesian DNA comprises between 4% and 6% Denisovan DNA.
David Reich from the Harvard Medical School, who worked with Svante
Paabo on the study, says that the fact that Denisovan genes ended up so
far south suggests they were widespread across Eurasia: "These
populations must have been spread across thousands and thousands of
miles," he told BBC News.
One mystery is why the Denisovan genes are unique in modern Melanesians
and are not found in other Eurasian groups that have so far been
sampled.
'Fleeting encounter'
Professor Stringer believes it is because there may have been only a
fleeting encounter as modern humans migrated through South-East Asia and
then on to Melanesia.
The remains were excavated at a cave site in southern Siberia
"It could be just 50 Denisovans interbreeding with a thousand modern
humans. That would be enough to produce this 5% of those archaic genes
being transferred," he said.
"So the impact is there but the number of interbreeding events might
have been quite small and quite rare."
No one knows when or how these humans disappeared but, according to
Professor Paabo, it is very likely something to do with modern people
because all the "archaic" humans, like Denisovans and Neanderthals
disappeared sometime after Homo sapiens sapiens appeared on the scene.
"It is fascinating to see direct evidence that these archaic species did
exist (alongside us) and it's only for the last few tens of thousands of
years that is unique in our history that we are alone on this planet and
we have no close relatives with us anymore," he said.
The study follows a paper published earlier this year by by Professor
Paabo and colleagues that showed there was interbreeding between modern
humans and Neanderthals as they emerged from Africa 60,000 years ago. |
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