Oldest DNA ever found sheds light on humans' global trek

www.centnews.com ^ | 2014-10-22 18:00:08 | Richard INGHAM

[Red Badger]

France - Scientists said Wednesday they had unravelled the oldest DNA ever retrieved from a Homo sapiens bone, a feat that sheds light on modern humans' colonisation of the planet.

A femur found by chance on the banks of a west Siberian river in 2008 is that of a man who died around 45,000 years ago, they said.

Teased out of collagen in the ancient bone, the genome contains traces from Neanderthals -- a cousin species who lived in Eurasia alongside H. sapiens before mysteriously disappearing.

Previous research has found that Neanderthals and H. sapiens interbred, leaving a tiny Neanderthal imprint of just about two percent in humans today, except for Africans.

The discovery has a bearing on the so-called "Out of Africa" scenario: the theory that H. sapiens evolved in East Africa around 200,000 years ago and then ventured out of the continent.

Dating when Neanderthals and H. sapiens interbred would also indicate when H. sapiens embarked on a key phase of this trek -- the push out of Eurasia and into South and later Southeast Asia.

The new study, published in the journal Nature, was headed by Svante Paabo, a renowned geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who has pioneered research into Neanderthals.

- Neanderthal interbreeding -

The bone found at the Irtyush River, near the settlement of Ust'-Ishim, carries slightly more Neanderthal DNA than non-Africans today, the team found.

But it takes the form of relatively long strips, whereas Neanderthal DNA in our genome today has been cut up and dispersed in tiny sections as a result of generations of reproduction.

These differences provide a clue for a "molecular calendar", or dating DNA according to mutations over thousands of years.

Using this method, Paabo's team estimate interbreeding between Neanderthals and H. sapiens occurred 7,000 to 13,000 years before the Siberian individual lived -- thus no more than 60,000 years ago.

This provides a rough date for estimating when H. sapiens headed into South Asia, Chris Stringer, a professor at Britain's Natural History Museum, said in a comment on the study.

If today's Australasians have Neanderthal DNA, it is because their forebears crossed through Neanderthal territory and mingled with the locals.

"The ancestors of Australasians, with their similar input of Neanderthal DNA to Eurasians, must have been part of a late, rather than early, dispersal through Neanderthal territory," Stringer said in a press release.

"While it is still possible that modern humans did traverse southern Asia before 60,000 years ago, those groups could not have made a significant contribution to the surviving modern populations outside of Africa, which contain evidence of interbreeding with Neanderthals."

Anthropologists suggest a northern branch of Eurasians crossed to modern-day Alaska more than 15,000 years ago via an "ice bridge" that connected islands in the Bering Strait, thus enabling H. sapiens to colonise the Americas.

[Verginius Rufus]

Maybe the most dangerous is other Homo sapiens.

[SunkenCiv]

Thanks Red Badger.

The Neandertal Enigma
by James Shreeve
in local libraries

"Frayer's own reading of the record reveals a number of overlooked traits that clearly and specifically link the Neandertals to the Cro-Magnons. One such trait is the shape of the opening of the nerve canal in the lower jaw, a spot where dentists often give a pain-blocking injection. In many Neandertal, the upper portion of the opening is covered by a broad bony ridge, a curious feature also carried by a significant number of Cro-Magnons. But none of the alleged 'ancestors of us all' fossils from Africa have it, and it is extremely rare in modern people outside Europe." [pp 126-127]

[SunkenCiv]

Someone’s professor said it, someone believes it, that settles it. :’)

[SunkenCiv]

/bingo

[Verginius Rufus]

I think the differences between horses and donkeys are much greater than between Neanderthals and Cro-Magnons. If I remember rightly, horses and donkeys have different numbers of chromosomes.

How did Neanderthals and Cro-Magnons interbreed? Sounds like a topic for a federal research grant. "Hey, baby, want to see my cave paintings?" Did Cro-Magnons need beer goggles?

[BroJoeK]

“Where did Neanderthals originate?
Did they originate somewhere else or are they just a different offshoot of hominids?”

The way to think of it is, over the past millions of years, dozens of hominid species evolved in Africa, each a little smarter, a little more human - like than before.
Some of these species then migrated out of Africa, and when they met earlier species, they adapted, interbred and eventually replaced the earlier models.

Apparently, Homo-Neanderthal did not themselves leave Africa, but rather adapted/evolved in Europe from earlier species, now tentatively identified as “homo-anticesor”.
Neanderthals were in turn replaced by the latest emigrants, homo sapiens, beginning around 45,000 years ago.

[BroJoeK]

mountainlion: "These people come to a conclusion and call it a scientific fact.
It is still a conclusion and theory.
There are many theories and conclusions."

In scientific terms, a "fact" is a confirmed observation, while a "theory" is a confirmed hypothesis = explanation.
So, for examples, fossils and DNA are facts, while evolution and out-of-Africa are theories.

Barring some error in measurements, you don't expect facts to ever change, but theories can and often do change as new facts become known.

In this particular example, the new fact is DNA retrieved from very ancient bone, but everything explaining what it all means is based on theory -- i.e., radiometric dating, evolution, ancient pre-human migrations & interbreeding.
The new facts tend to confirm "out of Africa" theories, while providing possible dates for human-Neanderthal interbreeding.

But if you were hoping to find metaphysical or religious certainty in such science theories, then your expectations were highly unrealistic.

[BroJoeK]

Boogieman: "If you read Origin of the Species, that was really Darwin’s first step, casting doubt on the traditional notion of species, so that he could redefine the term to suit his purposes."

In fact, there was no strictly defined notion of "species", and indeed there is still not one today.
Humans have always bred and selected domesticated animals to suit our purposes, and so have long known of species' variability.
We've also known that some species cannot successfully interbreed with other -- the example of horse and donkey come to mind.

But the word "species" is strictly a modern construct, whose definitions have changed over time, and is even now changing to accommodate the latest in DNA analyses.
Thus, today a population can be designated a separate "species" even if it can successfully interbreed with others, but ordinarily does not.
If populations are biologically unable to interbreed, in the wild, they are considered not just separate "species", but also separate "genera".

Thus the example of polar bears and brown bears.
Until recent years polar bears were considered a separate genus from brown bears, but since we've seen confirmed examples of polar/brown bear interbreeding, they were reclassified as just separate species.

[mountainlion]

I agree except that “possible dates for human-Neanderthal interbreeding” is theory and not facts. There are conflicting theories as to whether Neanderthal and modern humans were coexistent. More data and DNA information are needed. DNA information could then be examined by statistics to determine if interbreeding actually took place.

[entropy12]

Interesting details. Thank you!

[BroJoeK]

Perhaps you are not aware of research over the past decade or so?
First of all, there’s no doubt at all that Neanderthals and biologically modern humans existed at the same times.
Indeed, if we use the usual date given for the first biologically modern humans, 200,000 years ago, then Neanderthals existed for the first 160,000+ years.

Obviously, not together at the same times & places until around 45,000 years ago, for maybe 10,000 years or so.
That’s when events got interesting, and nobody knows for sure what happened, except that when it was all over, Neanderthals were gone, and all non - Africans share up to 4% “Neanderthal DNA”.
So figuring out how & why that happened is a great quest of current research.

[mountainlion]

Perhaps you are not aware of research over the past decade or so?

There is not anywhere near 100% agreement on this. There are some interesting outcomes of DNA research. Chimpanzees have 95% of human DNA but a Carrot has 80% of human DNA.

[BroJoeK]

Well... Much depends on exactly how you measure things, but the usual numbers given put cows at 80%, fruit flies and chickens at 60%, and all forms of plant life below 50%.

Regardless, these numbers are a major piece of evidence supporting the hypothesis that all life on earth is at least remotely related and descended from distant common ancestors.