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#22897 07/23/07 11:00 PM
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New research supports the belief modern humans came out of Africa in a single wave (led by a Moses?):

http://newsfeedresearcher.com/data/articles_t29/idt2007.07.19.07.26.10.html

From the article:

"The team found that loss of genetic diversity was very closely mirrored by reduced physical variation the farther away people lived from Africa."

Of course this would be so even if humans descend from a single migration out of Africa in Homo erectus times. There is always less variation at the margins of a species' distribution because inbreeding and selection are greater. Genes from the centre or point of origin are also less able to reach all margins.

More from the article:

"Dr Andrea Manica and colleagues found all the skulls - 4,666 male and 1,579 female - bore striking similarities, giving support to the hypothesis that modern humans came fully developed out of Sub Saharan Africa"

If they all have a relatively recent common origin they should have more than "striking similarities", they should be almost exactly the same. Besides they would also have similarities if they had formed hybrids with any original population followed by selection.

I presume the genetic evidence they refer to is the mitochondrial DNA and Y-chromosome evidence I used in my "Adam and Eve" post. The following ancient SAGG link explains how these lines are reduced. Presumably the effect is not just confined to the period of modern humans:

http://www.scienceagogo.com/news/20040819224859data_trunc_sys.shtml

From that link:

"Scientists have puzzled over the fact that men's common ancestor, dubbed Y-chromosome Adam, seems to have lived around 100,000 years ago, whereas women's common ancestor, known as mitochondrial Eve, lived almost 200,000 years ago. Worldwide, the DNA from the Y chromosome has much less genetic variability than does mitochondrial DNA."

And this time more people are prepared to question the research:

http://anthropology.net/2007/07/21/anthropologists-dispute-latest-out-of-africa-claims/

From this link:

"Hawks has written up some more thoughts on his blog, in which he gives vent to his frustrations at what he clearly perceives as being a study that is fatally flawed from the outset, but has nevertheless grabbed the headlines, as so many similar ’single exodus’ claims have done in the past."

Now SAGG readers are no doubt sick of my saying it's because the idea can be interpreted as fitting in with biblical stories. I agree with the final statement in this link:

"The idea that much of the Pleistocene was populated by people living in a technical and cultural coma, only wakened from their collective slumber in the Upper Palaeolithic by the sudden pinprick of a modern intelligence which arose from a single location at a specific point in time, (enabling the florescence of our über-selves), is itself long overdue for consignment to the compost heap of old theories based on out-moded concepts."

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I had heard that lack of genetic diversity proved there had been a near mass extinction at some point. The point was named I just don't remember it. Large amounts of diversity reduced suddenly to small amounts making us more genetically homogenous as we were basically starting over.


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Scpg02. Bottleneck. I suspect the greatest selection in the human line was around the change from Australopithecus to Homo, about two to two and a half million years ago. Selection for tool-making and height.

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There was also a suggested bottleneck at 74k bp, following the Toba eruption, but this has since been disputed - J Hawks has a post

http://johnhawks.net/weblog/reviews/archaeology/middle/petraglia_toba_india_continuity_2007.html

and regarding the latest OoA theory, he has this link

http://johnhawks.net/weblog/reviews/earl....html?seemore=y

Terry - thanks for the mention over at Anthropology.net - my main objection to stories like these is that they propose a complete replacement model, whereby 'stupid old cavemen' or whatever, were
made extinct by our modern species which was supposedly vastly superior in intelligence etc, to all that went before - which, imo, is not only wrong, but can be seen to be wrong just by a brief examination of the Lower and Middle Palaeolithic - early art and symbolic expression, indicative of language, plus evidence for evolution occurring at multiple locations across the globe, rather than a wave of terminator-style exodus events from Africa.

cheers, Tim

#22927 07/25/07 09:54 AM
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Thanks TimJ07. One reply on a link from the second site:

http://science.slashdot.org/article.pl?sid=07/07/19/1438241

As option 2 wrote:

"The populations of the various continents split apart, but there is sufficient gene flow for mutations originating in one part of the world to spread to another. By coincidence or some process I'm not familiar with, the mutations arising in Africa spread to Europe and Asia, and those arising elsewhere spread to Africa. However, Europe and Asia have less genetic exchange, even with Africa acting as an intermediary."

The writer prefers his option 3 the single origin recent out of Africa scenario but his comment regarding option 2, "By coincidence or some process I'm not familiar with" seems rather silly. After all humans have been wandering into and out of Africa continually in historic times. But the writer obviously believes modern humans are the only species capable of such movement and hybridization.

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Maybe this has implications for what, or who, came out of Africa.

"Kenyan Fossils May Add New Branch to Human Family Tree" http://news.nationalgeographic.com/news/2007/08/070808-early-humans.html

"Traditional evolutionary theories of the genus Homo suggest a successive progression: Homo habilis gave rise to Homo erectus, which then begat modern humans, Homo sapiens."

..but...

"The finding indicates the two species lived side-by-side for half a million years in eastern Africa, according to study lead author Fred Spoor, a professor of evolutionary anatomy at University College London."


"Time is what prevents everything from happening at once" - John Wheeler
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Thanks Rede. I hadn't seen that version but both the anthropology and John Hawks blogs have articles on the two fossils. They provide a different perspective. Scroll down to the"man bites dog" article in the first one:

http://johnhawks.net/weblog/

http://anthropology.net/2007/08/08/the-ilert-fossils/

And this guy really gets stuck in:

http://scienceblogs.com/afarensis/2007/08/09/the_ileret_skulls_my_two_cents/

Seem likely to me that H. erectus evolved outside Africa from a H. habilis (whatever that species is, it varies considerably) and then moved back into Africa. Over time these two species interbred and produced the hand-axe.


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