Homo Longi Were Probably Denisovans

Homo longi ("Dragon men") the new species identification temporarily assigned to a Chinese specimen with a mix of archaic and modern features was probably one of a fairly heterogeneous species of hominin known genetically as Denisovans after the cave in Siberia where their DNA was first characterized. They were the predominant post-Homo erectus hominin of Asia and modern Papuans and Australian aborigines have particularly high level of Denisovan admixture which is present at trace levels in other Asians and in the indigenous peoples of the Americas. 

Their facial structure, although not necessarily their stature or build, resembles the typical artistic depiction of J.R.R. Tolkien's dwarves. An artist's impression of this archaic hominin previously known only from teeth and DNA is as follows:

 

Background and Analysis

The images above (via John Hawks) capture the big picture of archaic hominins. As Razib Khan explains, setting the background:

In 2010, genomes recovered from ancient remains of “archaic hominins” in Eurasia turned out to have genetic matches in many modern humans. . . . we had to get used to the new reality that a solid 2-3% of the ancestry of all humans outside Africa is Neanderthal. About 5% of the ancestry of Melanesian groups, like the Papuans of New Guinea, actually comes from a previously unimagined new human lineage discovered in Denisova cave, in Siberia of all places. . . . Trace, but detectable (0.2% or so), levels of “Denisovan” ancestry are found across South, Southeast, and East Asia (as well as among indigenous people of the Americas). Similarly, trace but detectable levels of Neanderthal ancestry actually appear in most African populations. And, though we have no ancient genomes to make the triumphant ID, a great deal of circumstantial DNA evidence indicates that many African groups harbor silent “archaic” lineages equivalent to Neanderthals and Denisovans. We call them “ghost” populations. We know they’re there in the genomes, but we have no fossils to identify them with. . . . an Israeli group has a paper out in Science on a human population discovered there which seems to resemble Neanderthals and dates to 120,000 to 140,000 years ago. . . .

Neanderthals, Denisovans, and modern humans are just the main actors in the plotline of our species’ recent origins. Today on our planet there is just one human species, but this is an exceptional moment. For most of the past few million years there were many human species. Up until 50,000 years ago in the Southeast Asian islands of Flores and Luzon, we see strong evidence of very specialized species of small humans, the pygmy Hobbits and Homo luzonensis. They are different not only from each other, but from modern humans, Denisovans and Neanderthals. In Africa, there were almost certainly very different human populations which over time were absorbed, just as the Denisovans and Neanderthals were. Homo naledi in South Africa almost certainly persisted down to the period of the rise of modern humans on the continent, 200,000 years ago.

Finally, a great deal of circumstantial archaeological and genetic evidence is accumulating that some earlier African lineages related to modern humans expanded out into eastern Eurasia before our own expansion. Artifacts in China and Sumatra dating to before 60,000 years ago seem suspiciously modern, and genetic analysis of Siberian Neanderthals dating to 120,000 years ago suggests admixture from populations related to modern humans. It is still possible that Homo longi descends from one of these early populations. Only DNA can establish this for a fact, but most older fossil remains do not yield genetic material, and this skull is old enough that only perfect conditions would have yielded DNA.

Ancient hominins from China ca. 200,000 to 100,000 years ago with a mix of archaic and modern features were probably Denisovans. John Hawks calls them "H. antecessor groups with the Jinniushan-Dali-Harbin-Xiahe clade." 

A new published journal article describes a specimen skull from these archaic hominins and puts them in context. Morphologically, it is closer to modern humans than to Neanderthals, although Denisovan DNA is shares a clade closer to Neanderthals than to modern humans (within the clade that all three share), and this is likely what this specimen is (although we don't have DNA to confirm it). It is akin to several other roughly contemporaneous sets of remains from Asia:

Razib Khan has this commentary:

Some researchers want to call “Dragon Man” Homo longi (龙, pronounced lóng, being Chinese for dragon), a new human species, and assert its features mean it is more closely related to modern humans than Neanderthals. This is particularly true of the Chinese researchers, in whom I can’t help but sense a drive to establish precedence for China as one of the major hearths of modern humans.*

Paleoanthropologists outside of China seem more inclined to believe that “Dragon Man” is actually the paradigm-busting species we have only known definitively from genomics: Denisovans. This faction points out that “Dragon Man” had massive teeth, just like a confirmed Denisovan jaw discovered in Tibet in 2019 (ancient-protein analysis indicated it was Denisovan). So why do others disagree? Because the skull is so intact they performed an evolutionary analysis of its relationships, using a full suite of characteristics (unfortunately the find did not yield DNA). On that inferred family tree, Homo longi lies closer to modern humans. In contrast, we know from genomics that Denisovans are more closely related to Neanderthals than they are to modern humans.

My bet is that Homo longi and Denisovans are one and the same. Or, more precisely, Homo longi is one of the many Denisovan lineages. 

. . .

The best genetic work indicates that Denisovans were not one homogeneous lineage, as seems to have been the case with Neanderthals, but a diverse group that were strikingly differentiated. The Denisovan ancestry in modern populations varies considerably in relatedness to the genome sequences from Denisova cave. It is clear that the Denisovan ancestry in Papuans is very different from the Siberian Denisovan sequences. The most geographically distant Denisovan groups, those in Siberia and those from on the far edge of Southeast Asia into Wallacea, were likely far more genetically different from each other than Khoisan are from the rest of humanity. Depending on the assumptions you set your “molecular clock” with, the most distant Denisovan lineages probably separated into distinct populations from each other 200,000 to 400,000 years before their extinction.

John Hawks states in a Tweet:

Now, we have learned a few things from DNA and ancient proteins. H. antecessor is a sister of the Neandertal-Denisovan-modern clade. Neandertals, today's humans, and Denisovans share common ancestors around 700,000 years ago. Neandertals and Denisovans were related.

I agree that the Homo longi remains are probably Denisovans. 

The main new article is Xijun Ni, "Massive cranium from Harbin in northeastern China establishes a new Middle Pleistocene human lineage" The Innovation (June 25, 2021) (open access).