Modern Humans Interbred with Two Groups of Denisovans

There is now more evidence that were were “one big happy family.”  Here is a short recap:

Beginning around 1.8 million years ago, a hominin form called Homo erectus left Africa for points east, eventually settling in Indonesia and China. These early humans were characterized by having heads roughly ¾ the size of modern humans with very large brow ridges and with their widest point just above the ears. They were also the first humans to conquer fire and perfect hunting.

Then, at some point, between 300 and 500 thousand years ago, a population group migrated from North Africa into Europe and, eventually into East Asia. The European branch became the Neandertals, between 200 and 250 thousand years ago, and the East Asian group eventually became the Denisovans. The Denisovans then spread east and south, eventually mixing with other populations, some of which were the precursors of the Melanesians and native Australians. The bulk of the Neandertals hunkered down in Europe and tried to outlast the bitter cold of not one but two glaciations.  Despite this, while often pilloried in cultural literature as being half-witted brutes, Neandertals were a very complex society, with advanced weaponry and hunting behavior, grave goods, habitation structures and who practiced ritual behavior. Some populations of Neandertals eventually  expanded their range into Western Asia and steppic Russia and interbred with the Denisovans.  Unfortunately, as a culture, we know next to nothing about the Denisovans. 

Roughly 100 thousand years after this, there was yet another wave of migration, between 100 and 60 thousand years ago, of early modern humans from North Africa, who moved north and East mixing with both the Neandertals in Europe and, perhaps, Western Asia and the Denisovans in East Asia.

And now we learn that the modern humans arriving from Africa interbred with not one but two groups of Denisovans.  From Gizmodo:

We know so little about the Denisovans that they don’t even have a formal scientific name, though scientists are considering Homo sp. Altai or Homo sapiens ssp. Denisova. Indeed, as these names suggest, Denisovans were a branch of humans, having diverged from Neanderthals some 200,000 years ago. We know this because the Altai fossil yielded a near-complete genome, which scientists have been poring over since it was first sequenced in 2010.

But in addition to the Neanderthal ancestry, genetic anthropologists also learned that Denisovan DNA lives on in modern humans, especially among Oceanians and East and South Asians. This means anatomically modern humans, or Homo sapiens, must’ve interbred with a population of Denisovans. But as new research published today in the science journal Cell points out, our ancestors mated with Denisovans on at least two different historical occasions. So the traces of Denisovan DNA embedded in the genomes of some people living today originated from at least two distinct Denisovan populations.

Given Palaeolithic population densities, this is not surprising.The research seems to indicate that there were early modern human/Denisovan mixes in both Asia and Oceania.  What this means is that, once the Denisovans and Neandertals split, the Denisovans migrated east and northeast (as humans will do) and established population centers in these areas.  When the modern humans came (Huh.  I wonder what is over that hill?  Oh look, humans...sort of.) it made sense to intermingle with them.  We already know that Neandertals and modern humans could, and did, mix.  It is, absent any knowledge to the contrary, reasonable to assume that the Denisovans looked mostly modern human. 

Interestingly, the research seems to indicate that the rate of interbreeding of Neandertals to early moderns was much more limited than with moderns and Denisovans.  This is at variance with other studies (and fossil material) which seems to indicate more sustained contact.  It would be nice if we could find a bit more fossil evidence to get a handle on what at least one Denisovan looked like. 

Mount Carmel Caves Nominated to Join World Heritage List

Four caves that have extensive evidence of human Palaeolithic occupation have been placed on the World Heritage List. They are Tabun, Jamal, El-Wad and Skhul. Tabun and Skhul are near and dear to the heart of every palaeoanthropologist as being the site of the early modern and Neandertal remains described in The Stone Age of Mount Carmel, by McCown and Keith, which was published in 1937. The story, from the Jerusalem Post, notes:

The sites are “located in one of the best preserved fossilized reefs of the Mediterranean region” and contain cultural deposits filled with 500,000 years of human evolution, from the Lower Paleolithic era to the present day, said a summary document that the World Heritage Committee printed in May.

The Nahal Me’arot caves provide “a definitive chronological framework at a key period of human development,” according to the summary document. Archeological evidence found in the region indicates the appearance of modern humans who conducted deliberate burials and who were exploring early stone architecture, as well as transitioning from hunting and gathering to agricultural processes.

This is long overdue. The Mount Carmel area is also traditionally where Elijah struck down the prophets of Baal.

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Werner Herzog Tackles the Upper Palaeolithic

Acclaimed filmmaker Werner Herzog has directed a documentary on Chauvet Cave in France, where the walls are covered in artwork that dates to around 30,000 years ago. Chris Garcia, writing for the Wall Street Journal, has this to say:

Because the cave is accessible only to scientists, Mr. Herzog had to acquire special permission from the French government to film inside and had to adjust to extreme time and technical limitations, using a crew of only four.

What the veteran filmmaker, 70, discovered inside was a world of subterranean splendor, namely cave paintings in pristine condition—Ice Age menageries of rhinos, lions, mammoths, bison and cave bears, amid glistening lunar-like surfaces.

The film has been shot in 3D and will be out at the end of April in the larger cities and then other places later. The funny quote from the interview, however, is about Woody Allen:

CG: You're an extremely fast filmmaker, a lot like Woody Allen.

WH: Woody Allen is like a snail. He makes a film a year. I make two to three films a year.

Now, that's funny.

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From Bottleneck to Expansion

Once modern humans began to assert themselves on the landscape, data suggests they took off. ScienceDaily is reporting that beginning around 40 000 years ago, the human population began expanding:

Reconstructions of the timing and magnitude of changes in human population size are important for understanding the evolution of our species. There has been a longstanding disagreement whether humans began to increase in number as a result of innovative technologies and/or behaviors formulated by hunter-gatherer groups in the Late Pleistocene, or with the advent of agriculture in the Neolithic. Hammer's research integrates empirical genetics with discoveries in paleontology and archeology to help provide answers to interdisciplinary questions about which kinds of innovations led to the evolutionary success of humankind.

The article appears in PLoS One and can be read here. The authors conclude:

The data from the three surveyed non-African populations (French Basque, Chinese Han, and Melanesians) are inconsistent with the simple growth model, presumably because they reflect more complex demographic histories. In contrast, data from all four sub-Saharan African populations fit the two-phase growth model, and a range of onset times and growth rates is inferred for each population. Interestingly, both hunter-gatherers (San and Biaka) and food-producers (Mandenka and Yorubans) best fit models with population growth beginning in the Late Pleistocene. Moreover, our hunter-gatherer populations show a tendency towards slightly older and stronger growth (~41 thousand years ago, ~13-fold) than our food-producing populations (~31 thousand years ago, ~7-fold). These dates are concurrent with the appearance of the Late Stone Age in Africa, supporting the hypothesis that population growth played a significant role in the evolution of Late Pleistocene human cultures.

The late Stone Age at this point coincides with the recession of the ice at the tail end of the Late Würm glaciation and is coincident with the appearance of modern humans in Europe and several other areas of the Old World. It also accounts (at least in part) why technology takes off at such a fantastic clip beginning with the Upper Palaeolithic period. A critical mass of people drive new ideas and technology. It also helps that your tundra line doesn't begin at Vienna.

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The Axe That Roared

Maev Kennedy of The Guardian has a story about an axe that was found in a quarry by John Evans and Joseph Prestwich that has reappeared after 150 years. According to the story:

On 26 May 1859, six months before Charles Darwin shattered the biblical creation story when he finally plucked up the courage to publish his theory of natural selection, the stone hand axe from the bottom of a French quarry was presented to the world at a lecture at the Royal Society in London.

Neither John Evans nor Joseph Prestwich, the businessmen and amateur archaeologist and geologist who found it, nor their distinguished audience, could guess its true age, around 400,000 years. But they did know it came from "a very remote period", when the woolly mammoth and rhinos, whose bones were mixed up in the same layer, roamed the plains of northern France.

There was no way the mammoths and the man-made tool could be fitted into the traditional biblical timescale, calculated by the 17th-century Archbishop Ussher, that God made the world in 4004BC.

The axe then vanished for 150 years, until it was tracked down by another archaeologist and geologist team – Clive Gamble, a professor at Royal Holloway, and Robert Kruszynski of the Natural History Museum – who publish their quest in next month's Antiquity journal.

It is important to note that this was not the first stone tool to come out of the ground and that people were starting to get some odd ideas about just how literal the biblical creation story actually was. The Spy Neandertals had been unearthed in Belgium, in 1828, the Feldhofer cranium in the Neander Valley, in 1856, and other finds had come to light, as well. The axe was special because it showed prehistoric occupation of England, which had spent most of its time under large sheets of ice.