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. 

New Ancestral Native American Population Discovered: The YEC Interpretation

On the heels of the discovery of the new ancestral Native American DNA, several young earth creationists have claimed that the discovery supports the global flood model and a young earth.

Uh huh.

From the Baptist Press:

After scientists extracted the DNA, they dated it to approximately 11,500 years ago, according to common evolutionary dating methods, and discovered commonalties between the harvested genome and the DNA of modern Native Americans. Researchers also found the ancient infant girl had ancestors in East Asia some 35,000 years ago according to evolutionary dating methods.

The finding marks the second oldest human genome ever discovered in North America, The New York Times reported.

Nathaniel Jeanson, a Harvard-trained research biologist with Answers in Genesis (AiG), told Baptist Press the dating of the Alaska DNA seems to be inaccurate. But other details of the find, he noted, corroborate the account in Genesis 11 of mass human migration following attempted construction of the Tower of Babel.

The Nature study, Jeanson said, is “more evidence for people in the Americas from Asia -- East Asia, Central Asia" and "is consistent with Scripture.”

It is also consistent with every single model of population movement into the New World since the 1970s. It may be the oldest DNA found in the New World, but it still supports all of the previous models.  And, on what basis is the dating wrong?  Jeanson is willing to take everything else at face value, including the idea that this represents the first peopling of the New World.

How would he know this if the dates are wrong?  Again, from the article:

Kurt Wise, a Southern Baptist and Harvard-trained paleontologist, told BP in written comments the 11,500 "radiocarbon years" cited by Nature "amount to many fewer true (chronological) years (probably closer to 4,000-4,100 years)."

"If one considers the ages" given by Nature “in relative terms, the new findings are consistent with a dispersion of humans from Babel,” said Wise, professor of natural history at Truett McConnell University, “people making it to western-most Europe, southern-most Africa, and eastern-most Asia first, then coming through the Bering Strait from western Asia into what is now Alaska ... and spreading from there into northern, central, and southern South America.

“So, these remains,” Wise said, "are most probably of a population of people spreading out from Babel” -- a reality he termed “rather exciting!”

How does one take the dates ”in relative terms?”  That is why they call it absolute dating.  Relative dating is when something is older than something else based on its position in the geological column.   Additionally, the reason that we can identify it as a population that is ancestral to later Native Americans (some of them, anyway) is because of the genetic similarities to very-eastern Siberian and north Chinese populations that existed some 30 to 40 thousand years ago in those areas and who's descendants migrated over the Bering Strait.

If the flood really had happened sometime between 2400 and 2500 B.C., there would be no such genetic diversity.  Everyone would have very similar DNA and it would be traceable to some area around northeastern Turkey/southern Armenia/Black Sea.  Yet those people are very distinct, genetically from east Asians and Europeans. 

In short, this DNA strand constitutes no evidence, whatsoever, for a migration of people after the Noachian Flood.   

Another Human Species in China?

The Christian Science Monitor and other outlets are reporting on a new find from Xuchang, China, that seems to possess intermediate traits between archaic and modern Homo sapiens:

In an article published Friday in the journal Science, the researchers note that the skull fragments date to the Late Pleistocene epoch, a time marked by the expansion of H. sapiens and the extinction of other species in the genus Homo. During the early part of that epoch, Neanderthals roamed Europe and western Asia while humans began to journey out of Africa. But fossil records of human species in Eastern Asia from that time period are thin, muddying the picture of that era for a substantial region of the planet.

The skulls found in China were found to bear very close resemblances to those of Neanderthals, including a very similar inner ear bone and a prominent brow ridge. But the brow ridge was much less pronounced than one would expect from Neanderthals, with a considerably less dense cranium, as one might expect in an early H. sapiens. Researchers also found that the skulls were large by both modern and Neanderthal standards, with a whopping 1800 cubic centimeters of brain capacity.

So where do they fit in the grand scheme of things?

"The overall cranial shape, especially the wide cranial base, and low neurocranial vault, indicate a pattern of continuity with the earlier, Middle Pleistocene eastern Eurasian humans. Yet the presence of two distinctive Neanderthal features ... argue for populational interactions across Eurasia during the late Middle and early Late Pleistocene," said Dr. Trinkaus in a statement.

This kind of population mixing makes sense. We already know that modern humans and Neandertals interbred in Europe and that the geographic range of Neandertals stretched from Portugal to Teshik Tash, in Russia and Shanidar Cave, in Iraq.

The remains are dated to Marine Oxygen Isotope Stage 5d or 5e, making them between 105 and 125 ky in age.  Here is a description of the neurocranium from the paper:

The large Xuchang 1 neurocranium closely approximates the shapes of those of Middle Pleistocene humans, especially eastern Eurasians (Fig. 2 and fig. S17). The vault height is low, similar to those of the Neandertals and the higher Middle Pleistocene vaults, and the low vault height is reflected in a low temporal squamous portion (figs. S27 and S28). It is also produced by the very flat midsagittal parietal arc. In contrast, the maximum cranial breadth is the largest known in the later Pleistocene (fig. S15), and it is securely based on an undistorted posterior cranium. Moreover, the widest point is low, on the temporal bones (fig. S17), as in most earlier crania, rather than on the parietal bones, as among Neandertals and most modern humans. In addition, the one complete mastoid process is short and slopes inward (fig. S17), rather than being longer and more vertical, as in modern humans and some Neandertals. These features combine to provide the cranium with an occipital profile similar to those of earlier human crania, contrasting with the rounded profiles of Neandertals and the laterally vertical ones of modern humans.

There are a few things that are immediately interesting about this. First, this skull is YUGE.  1800 cc is monstrous.  The average cranial capacity of modern humans is around 1450 cc and that of Neandertals, around 1550 cc.  Second, the low, flat cranium with the widest point on the temporal bones (just above your ears) are traits of Homo erectus, not modern humans or Neandertals, suggesting strongly that there was some sort of continuity from this group through to modern humans in this region.  Neandertals simply don't have those traits.  Nonetheless, the cranium clearly shows some Neandertal traits in the ear and rear of the vault.  This continuity is characterized by the authors thus: "This morphological combination, and particularly the presence of a mosaic not known among early Late Pleistocene humans in the western Old World, suggests a complex interaction of directional paleobiological changes and intra- and interregional population dynamics."  As more information becomes available, we will have a better idea of how this find fits in the east Asian evolutionary picture.  This is exciting.  Up until this point, we have had very few finds in China that fall within this general time frame, most notably the Dali and Mapa remains.  I will have to rework my section on human origins for the BioLogos site for this region.