New Jebel Irhoud Date Causes Rethink of Chinese Dali Skull

Newsweek (Yes, that Newsweek) has a story on the reexamination of the Chinese Dali cranium, in light of the revised dates for the Jebel Irhoud skulls.  Kastalia Medrano writes:

Known as the Dali skull, it was discovered nearly 40 years ago in China’s Shaanxi province. It belonged to a member of the early hominin species Homo erectus. Its facial structure and brain case are intact, despite being dated to around 260,000 years ago. The Dali skull is so old that archaeologists initially didn’t believe it could share features with the modern Homo sapiens.

But Xinzhi Wu of the Chinese Academy of Sciences in Beijing believed that due to the overwhelming physical similarities, Homo erectus must have shared DNA with Homo sapiens. After decades of this idea being dismissed by mainstream academia, Wu and a colleague, Sheela Athreya of Texas A&M University, recently reanalyzed the Dali skull and found it may force us to rewrite our evolutionary history after all. It’s incredibly similar to two separate Homo sapiens skulls previously found in Morocco. “I really wasn’t expecting that,” Athreya told New Scientist.

If we’d found only the Moroccan skulls, and not the Dali skull, it would make sense to keep believing all modern humans evolved in Africa. But the similarities show that early modern humans may not have been genetically isolated from other parts of the world, like what we know today as China.

“I think gene flow could have been multidirectional, so some of the traits seen in Europe or Africa could have originated in Asia,” Athreya told New Scientist.

Okay, now the nuts and bolts.Dali has always been thought to occupy that rarified space between Homo erectus  and early modern Homo sapiens.  It was always thought to be between 200 and 250 kya, and optically-stimulated luminescence dating (a variant of thermoluminescence) places it between 258 and 267 kya.  My analyses of the skull suggested that it was, in no way, shape or form, a modern human but it did not tend to cluster with the Neandertals in terms of head shape.  Athreya and Wu have done an extensive multivariate analysis and conclude (from the article, likely behind a paywall:

When just the facial skeleton is considered, Dali aligns with Middle Paleolithic H. sapiens and is clearly more derived than African or Eurasian Middle Pleistocene Homo. When just the neurocranium is considered, Dali is most similar to African and Eastern Eurasian but not Western European Middle Pleistocene Homo. When both sets of variables are considered together, Dali exhibits a unique morphology that is most closely aligned with the earliest H. sapiens from North Africa and the Levant.

These results add perspective to our previous view of as Dali a “transitional” form between Chinese H. erectus and H. sapiens. Athough no taxonomic allocation is appropriate at this time for Dali, it appears to represent a population that played a more central role in the origin of Chinese H. sapiens. Dali's affinities can be understood in the context of Wu's Continuity with Hybridization scenario and a braided-stream network model of gene flow. Specifically, we propose that Pleistocene populations in China were shaped by periods of isolated evolutionary change within local lineages at certain times, and gene flow between local lineages or between Eastern and Western Eurasia, and Africa at other times, resulting in contributions being made in different capacities to different regions at different times.

In combination with the Xuchang remains, the reanalysis of this skull suggests that, indeed, there is a long and complex interrelationship between different hominin groups that dates back some 400 thousand years. From the paper:

In the braided-stream network model, evolutionary change in China was the result of a shifting network of gene flow among distinct regional Chinese populations, as well as between Chinese and Western Eurasian populations. These were not isolated evolutionary lineages; gene flow both within China and between Eastern Eurasia, Western Eurasia and Africa was intermittent and could explain the similarities in aspects of the neurocranium found here between Dali and Western Eurasian Middle Pleistocene humans. Gene flow would best be described as a braided stream network with periods of isolated evolutionary change within a local lineage at times, and periods of gene flow between local lineages or paleo-demes at other times, resulting in contributions being made in different capacities to different regions at different times.

It is pretty clear that our simplistic models of Recent African Replacement and Multiregional Evolution need to be reworked. It is becoming more apparent that what we are looking at either a polytypic species with a huge geographical range or a syngamion of related species that intermixed regularly. The Xuchang skulls were, apparently, not unique.

PhysOrg: Research Team Discovers "Immune Gene" in Neanderthals

Neandertals once again appear to be playing a central role in modern human origins and continued viability.  From PhysOrg:

A research group at Bonn University, Germany, and international collaborators discovered a novel receptor, which allows the immune system of modern humans to recognize dangerous invaders, and subsequently elicits an immune response. The blueprint for this advantageous structure was in addition identified in the genome of Neanderthals, hinting at its origin. The receptor provided these early humans with immunity against local diseases. The presence of this receptor in Europeans but its absence in early men suggests that it was inherited from Neanderthals. The results have been published in advance online in the Journal of Biological Chemistry. The printed edition is expected in a following issue.

Whether or not it predates Neandertals will never be known but the fact that it has time-depth back that far suggests that this receptor evolved separately from the incipient modern humans and that the interbreeding between the two was sufficient enough for it to take hold in some populations of modern humans. The report also notes that this receptor is very rare in Sub-Saharan Africans but is present in at least two-thirds of Europeans. 

I think we are just scratching the surface in terms of determining how much interbreeding went on between Neandertals and modern humans.  It is clear, judging from each new study, that the species lines are becoming more and more blurred. 

Study: Neandertal Speech and Language Abilities Like Modern Humans

Science Daily has a story on Neandertal speech.  Work by Dan Didiu and Stephen Levinson suggests that Neandertals and modern humans share a common ancestry with regard to the use of language.  Science Daily writes:

Dediu and Levinson review all these strands of literature and argue that essentially modern language and speech are an ancient feature of our lineage dating back at least to the most recent ancestor we shared with the Neandertals and the Denisovans (another form of humanity known mostly from their genome). Their interpretation of the intrinsically ambiguous and scant evidence goes against the scenario usually assumed by most language scientists, namely that of a sudden and recent emergence of modernity, presumably due to a single -- or very few -- genetic mutations. This pushes back the origins of modern language by a factor of 10 from the often-cited 50 or so thousand years, to around a million years ago -- somewhere between the origins of our genus, Homo, some 1.8 million years ago, and the emergence of Homo heidelbergensis. This reassessment of the evidence goes against a saltationist scenario where a single catastrophic mutation in a single individual would suddenly give rise to language, and suggests that a gradual accumulation of biological and cultural innovations is much more plausible..

I am still a bit “iffy” on the whole “common ancestor of modern humans and Neandertals” thing since some are trying to argue for a common ancestor based on the material from the Gran Dolina, in Spain, and it sure as all get out looks like modern humans originated in Northeast Africa at, or near, Herto. I have a tendency to think that there was a good deal of panmixia throughout Europe and north Africa.  Otherwise, we are required to believe that there was a species split at H. antecessor into what became modern humans (how'd they get to north Africa?) on one side and Neandertals on the other and that, some 700 to 720 thousand years later, emerging moderns and Neandertals encountered one another and interbred.  That is overly simplistic, I am sure but it seems far-fetched.  It seems easier to argue that the H. antecessor material represents an archaic Homo sapiens population that was the precursor (or something like it was) to later archaics, such as Petralona and Atapuerca, out of which Neandertals came.  Then the Neandertals interbred with the north-moving moderns and somewhere in there, the Denisova population split off.  The panmixia in Europe, western Asia and Russia explains why moderns have both Neandertal and Denisovan genes, along with the modern genes that originated in North Africa.  Subsequent swamping of the archaic genome led to the demise of both the Neandertals and Denisovans.   

Neandertal/Modern Human Hybridization in North Africa?

That is the focus of a new paper in PLoS ONE by Sanchez and colleagues.  Using 780 thousand single nucleotide polymorphisms of 125 individuals from populations in North Africa, they write:

We found that North African populations have a significant excess of derived alleles shared with Neandertals, when compared to sub-Saharan Africans. This excess is similar to that found in non-African humans, a fact that can be interpreted as a sign of Neandertal admixture. Furthermore, the Neandertal's genetic signal is higher in populations with a local, pre-Neolithic North African ancestry. Therefore, the detected ancient admixture is not due to recent Near Eastern or European migrations. Sub-Saharan populations are the only ones not affected by the admixture event with Neandertals.

Well, raise my rent! When we analyzed the modern human remains in the Near East using canonical variates analysis, we found that they showed more of a similarity with North African archaics than they did Neandertals and that this supported a model of a general northern migration of North Africans into the Levant between 100 and 200 thousand years ago. I will be interested to see the reaction to this from the morphologists.

Ironically, the bulk of the evidence supporting the admixture of modern humans and Neandertals has always been based on the fossil record, while the genetic evidence has traditionally been used to argue for a recent African origin. It is interesting to see all of the genetic studies that have turned the tables. There is not a specific level of admixture at which point you can say "hey, these are the same species," but the studies continue to come out suggesting that admixture was taking place wherever these two groups intermingled and that there do not seem to have been biological imperatives to mate.  They simply decided to do so.  Remember the sage words of J. Lawrence Angel: "When two groups of people meet, they may fight but they willl always mate."