Continuing with yesterday's post on possible entry of Homo erectus into America and their survival until relatively recent times, I decided to see if there was more data available and came across the following, which is indeed interesting as it changes the conventional view of how the world was peopled some fifty thousand years ago.
The traditional "linear" model is that man evolved in Africa from apes, which got brainier and at a given moment in time, walked out of Africa (such as the Homo erectus) to people the world while others stayed behind and continued evolving. The migrants (and nobody explains why [**]) remained static and did not change or evolve but those that remained behind did. So then came Homo heidlebergensis and Homo neanderthalensis who moved out of Africa and, finally, after more evolution towards better and bigger brains, we appeared, marched out of Africa and replaced all the others. Only modern man (Homo sapiens) managed to reach America (our 'superior' brains gave us the advantage and let us handle the tough Siberian and Alaskan climate and make it into the New World).
[**] Well, yes, there is a theory, the "Multiregional" one, which in sharp contrast with the "Out of Africa" theory states that modern man did not only appear in Africa, but that Homo erectus evolved in different regions (hence the theory's name) into modern men.
More varieties of humans?
However, the picture seems different: there were other people and also, they all lived at about the same time, sharing overlapping territories:
An article published on March 24, 2010 tells us about DNA extracted from a 40,000 year old finger bone found in a Siberian cave has yielded surprising results: it was not human and it did not belong to a Neandertal either (the only two possible sources of human bones!). It belongs to another New and hitherto unknown lineage of ancient humans. So that makes at least three kinds of humans (actually if we include the Flores Hobbits -Homo floresiensis, it makes four) sharing our planet some 40,000 years ago.
The finger bone was found at the Denisova Cave in 2008. The cave is located at the Altai Mountains in Russia, Central Asia, and has many archaeological layers that span nearly one hundred thousand years of occupation.
Neanderthal remains and modern men stone tools have been unearthed ther. Also broken bone remains, among which was this finger bone which has been radiocarbon dated to between 30 and 48 thousand years ago.
The bone was ground and a minute sample of Mitochondrial DNA (mtDNA) extracted for genetic sequencing.
mtDNA is a special variety of DNA which is found in cellular organelles called mitochondria, which are found inside every cell and help them produce energy.
mtDNA mutates (by chance) at a roughly given rate, and the accumulated mutations found in cells of different species give us an idea of how long they have been diverging apart from a common ancestor.
Now, for those not too familiar with the "drift" and mutations, please bear in mind that these are minute: Modern humans are, despite the differences that exist today between racial groups, a remarkably homogeneous population. A single species of chimpanzee has a difference five times greater than ours among its members!
Nevertheless, the differences exist and are a useful tool.
The mtDNA sample results
The group that sequenced this mtDNA had previously done similar work on Nenderthal genetic material.
The team then compared the finger's mtDNA with that Neanderthal and with modern human's mtDNA data discovering that:
- Neandertals differ from modern humans at an average of 202 nucleotide positions in the mitochondrial genome
- The Denisova "person" differed at an average of 385 positions from modern humans and 376 from Neandertals
Then they compared the Denisova mtDNA with that of chimpanzees (a common ancestor to all humans) and came up with an estimated age for the Denisova people: we H. sapiens, the Neanderthal and the Denisova people shared a common ancestor about one million years ago.
This is younger than the age of our other ancestor, the Homo erectus who left Africa shortly after it evolved roughly 1. 7 million years ago. And, on the other hand it is older than the departure date of the H. heidelbergensis (our and Neanderthal's nearest relative [*]), who is first recorded some 650 thousand years ago.
[*] H. heidelbergensis evolved from H. erectus in Africa and Europe, later evolving into modern man (in Africa), and Neanderthal (in Europe). [2]
So, the Denisova cave results is making scientists wonder if there may have been other hominds exiting Africa or that human evoultion is more like a flow of differing humans instead of a step by step linear process.
But what about H. erectus?
The article does not mention any Homo erectus mtDNA sequencing, so this had led me to wonder if the Denisova people were not simply h. erectus.
As only small bones have been found the telltale signs of an erectus small brain and thick brow bridge have not been found.
Why conjecture about another unknown species when we could simply state that these were surviving erectus.
If so, it is a clear sign that erectus, against common belief, persisted until quite late in mainland Asia (and not only in isolated Asian islands, as was the case I mentioned yesterday in Indonesia).
This time frame overlaps modern man, who may have entered America at that time some 30-40 thousand years ago (this is a highly controversial point as remains older than some 15,000 years in America are disputed and cause of heated debate among archaeologists).
The big "if" however is, "if erectus ever made it to America", because, as I mentioned yesterday, the proof on their presence here is sketchy, flimsy and not widely accepted. And we do lack firm evidence such as their characteristic stone tools, which would be a clear sign of their entry into the New World.
Read the final post (Part 3).
New on Dec. 23, 2010: Read more on the "Denisovians" and their possible link to modern Melanesians: Homo Erectus in America: More.
Sources
[1] Krause J, Fu Q, Good JM, Viola B, Shunkov MV, Derevianko AP, and Paabo S., (2010). The complete mitochondrial DNA genome of an unknown hominin from southern Siberia. Nature. 2010 Apr 8;464(7290):838-9.
[2] Frederick Lawrence Coolidge, Thomas Wynn, (2009). The rise of Homo sapiens: the evolution of modern thinking. Wiley-Blackwell, pp. 208.
Patagonian Monsters - Cryptozoology, Myths & legends in Patagonia
I have always considered that modern humans resemble a hybrid rather then one species. i would concentrate your research on 'conciousnous' as this varies remarkably between people and races. The facial and bodily differences of humans are immense as is the intellectual capacity albeit that I concede a social/development basis fre intellectual development
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