Do you think it worthwhile to separate African and Asian Erectus, i.e. Homo ergaster and Homo erectus?
No, I share in the broad consensus view that the fossils of Asian H. erectus and African H. ergaster are so similar that there is no basis to consider them as separate species. In modern terms we would call them different races, they are no more different than are African and Asian fully moderns living today. We now know that H. erectus were global, populating the world from Southeast Asia to Europe and Africa - a single relatively homogeneous species with regional variance in morphology that reflects the variance we see in modern humans across geographic regions today.
I fail to see how it falls under the "fact" category at all as to do so changes many of the very "facts" human speciation is built on in which it is these very differences that give classification to many of the different species and sub-species. Its ok to do away with this and chalk it up to variation, but to do so I think means the entire hominin line needs to be reevaluated all the same. To look at the Dmanisis skulls again, this is quite the motley crew:
Homo ergaster cranial capacity is between 700-900cc which I believe only skull 1 of the Dmanisi finds fall in this range at 780cc, whereas all the others are well below, around 600-650cc, with skull 5 at a meager 546cc. This kind of variation is found across other species as well, sometimes greater, including modern humans, so these differences in and of themselves are not enough regardless of the fact most are well below what is to be expected, but in conjunction with these are stark morphological differences which taken together I do not believe constitute variation within a species, but rather different species entirely. Further to consider is that such differences would be expected to be found across a large sample of the population, but this is the population at Dmanisi, all found together, which I do not believe such variance has ever been found in any species before, across the whole let alone within one group. Highly unusual.
You are right that this, if the academics at Dmanisi are correct, should prompt a rethink of the entire model we currently call the 'human family tree'. I am of the strong opinion that we need to completely update our model and do away with up to a dozen named species. The reality appears to be that Homo erectus ranged the planet in great numbers, they shared with modern humans a high degree of morphological diversity, indeed it may have been higher across regions as small groups broke off and moved into more isolated areas, preserving snapshots of the existing diversity at the time of separation. They also would have lived along side hominins that exhibited what we think of as archaic morphological traits, assuming they could breed with these (and we have no evidence against that and every reason to suspect they could) we would also see individuals with 'extreme' features preserved from non-erectus relatives included in their lineage. What we call genetic throwbacks.
The Dmanisi archaeological site is really out in the middle of nowhere, far from any other known hominin site that can be thought of as in any way related to it in any direct sense. Nobody even expected to find early hominins in the Caucasus region - it was a stunning site and a stunning blow for the consensus models. 1.8 million years ago the most advanced character in the field was Homo erectus, and it was supposed to be isolated in Africa. The leading experts have examined the skulls and concluded that they represent early Homo erectus, they do not all agree that these can be used to absorb the many named African hominins considered to have been co-existing, but they do agree these are Homo erectus. The fact that the five skulls are from a single small site and age a few thousand years apart makes it unreasonable to argue they can be from different populations, no matter how different they look, what population could they be from? We have found nobody else nearer to them than Africa - to suggest one or two might be another species would be REALLY hard to argue - imagine digging up a remote isolated cave in lion territory and finding four sets of ancient lion skeletons, and then a fifth that looked different. If we claimed this additional skeleton was a tiger rather than an odd looking lion I suspect our lapse in logic would be pointed out by all comers. Why would a lone tiger end up so far from its territory and be living among lions, how could it have ended up in the same grave site etc.
Could it be just possible another hominin species was around, maybe, but all of the leading experts that examined the skulls seem to be in agreement that they are five examples of Homo erectus - no matter what any of us may suspect. As I have stressed, I can't see a logical argument against this finding and I am not qualified to fully assess the morphology.
Right, but how does Homo habilis or the like get out of Africa let alone so far out of Africa? It makes no sense unless he (the "Dmanisi Habilis") originated outside of Africa as well which is not something most scientists, at least Out of Africa proponents which is the dominant view, are willing to consider.
It is no secret that I am very sympathetic towards the possibility that early humans, including Homo erectus, evolved outside of Africa. Indeed, I rather suspect all hominins share a non-African root, my suggestion would be they emerged in Southeast Asia - where early ancestral primates lived over 40 million years ago. The Dmanisi site alone is not enough to take down Out of Africa and re-position the origin of Homo erectus. The counter argument is that we have a long line of hominins in Africa, tool using early humans existing from 3.3 million years ago. The earliest accepted fossils of Homo erectus are in Africa, dated to 2 million years ago and of course the ancestor of these, Homo habilis (which I call early Homo erectus) is present 2.5 million years ago. This gives hundreds of thousands of years for a group of these beings to make there way out of Africa and up into the Caucasus. Much as it surprised academics, all they have to do is say, "oh well we missed the evidence of yet another earlier out of Africa migration".
Only by presenting hominin sites older than 1.8 million years that exist outside Africa can that argument be countered. It certainly also helps to find evidence of very early hominin forms outside Africa. For these reasons the best argument for the Dmanisi hominins being non-African comes in the form of the Masol hominin site in India (2.6 million years old) and the understood lineage of the Homo floresiensis 'hobbits', now that they have been fully assessed and attributed direct lineage to Homo habilis or a similar archaic lineage.
But why are they universally accepted as Erectus? This is what I am driving at as the only reason this is offered is to explain why they are all found together outside of Africa. If you took these skulls and placed them in different areas around Africa I guarantee they would not all be considered the same species with some being Habilis or the like and at least skull 1 being Erectus, with some I bet would even be hailed as a "new intermediary species" from Habilis to Erectus.
Apart from the logical argument already brought up, to which you are raising a finger here, there is another good reason why the skulls were accepted as a single species (in this case Homo erectus).
Were Earliest Humans All 1 Species? Oddball Skull Sparks Debate - LiveScience
The level of variation seen in Homo fossils is typically used to define separate species. However, the scientists found the level of diversity now seen between the five sets of fossils at Dmanisi — Skull 5 and the four other specimens — is no greater than any seen between five modern humans or five chimpanzees.
Christoph Zollikofer, a neurobiologist at the Anthropological Institute and Museum in Zurich
"If you take the biggest skull there and compare it to the smallest, the smallest one is 75 percent the size of the bigger one, and that's absolutely standard in what you would see in modern humans,"
It is this very morphological diversity that the multiple species (and sub-species) model is founded and if it is to be abandoned for the Dmanisi finds all other species need to be reevaluated as well.
Well, that really is the debate. One camp says we need to rethink the entire mess of early humans, the other says that until we have skeletons, rather than just skulls, we should not be so hasty.
This is true and many arguments have been made in this regard to other species, namely the myriad of sub species classifications, but also different genus i.e. Australopithecus and Paranthropus.
I am for merging the various Australopithecus together into one evolving lineage with extreme morphological variation in its midst, I call it Homo australopithecus (as tool use goes back at least 3.3 million years).
At this point either the morphology is enough to classify them separately, which personally for some I think it definitely is, or it isn't, though to some degree I would say the tool industry found has some say in this which in Homo erectus's case maybe the qualifier needed to distinguish them is "archulean" and "non-archulean" perhaps.
As we will never have DNA older thn 1.5 million years it does seem that morphology will remain the key criteria for identifying human species.
Though technically each can be assessed separately, I would say most definitely behavioral though they would appear to be directly related as it is not just how they "look", but rather it is this very morphology that allowed the human brain to develop to achieve such modernity, namely the higher vertical transition of the frontal bone that allowed the frontal lobe to more fully develop. Regardless, it is not our anatomy that sets us apart from other hominins but our behavior, ultimately the definition of what it means to be to be "human". To paraphrase James Shreeve from Neanderthal Enigma, the maddening thing about all species of hominins is that despite their long existence, they did not progress, i.e. build on previous successes, and if anything regressed towards their ends. Homo sapiens were no different as despite "modern humans" having been around for supposedly 200,000yrs he didn't start acting like a modern human until around 45,000yrs ago with the arrival of Cro-Magnon in Europe, who also just so happens to have the tell-tale cranial morphology of what we consider to be fully anatomically modern, something which is not present in Africa before. This means something.
It certainly makes most sense to look to behaviour, we see some very archaic looking fossils at very young sites and as such we can't say these people were not fully modern humans. Clearly they were part of fully modern human groups and we must imagine them doing all the same activities as individuals with more modern looking anatomy.
The consensus so far is sometime between 800,000-300,000yrs ago with recent analysis of a tooth suggesting this may have been earlier:
The new study contradicts this idea. The tooth reconstruction of the last common ancestor of humans and Neanderthals created by Gómez-Robles and colleagues doesn't match the teeth of H. heidelbergensis.
In fact, the researchers found that none of the human species living during the time predicted by genetic data fit the tooth pattern generated by the new study. More than that, "European species that might be candidates show morphological affinities with Neanderthals," Gómez-Robles says, which hints that these humans were already on the Neanderthal side of the split.
This suggests that the last common ancestor of H. sapiens and Neanderthals lived sometime earlier, perhaps as far back as one million years ago.
Much Earlier Split for Neanderthals, Humans?
The consensus used to include early dates, the 300,000 year old divergence being one. This has gone out the window following the Sima de Los Huesos genetic study (550 - 765 KYA) and indeed the University of Indiana comparative fossil research that gave the conclusion you are referring to when you mention the ancient tooth (1,000,000 YA). They actually looked at a very large number of teeth and jaw bones before concluding that there was no Homo sapiens ancestor in the fossil record of Europe and therefore also discounting Africa as the candidate species are reflected on both continents (Homo erectus and Homo heidelbergensis). If you also factor in the research at the Denisova cave site, which concluded Denisovans were diverging from our lineage by 800 KYA, you see why I point to 700 - 900 KYA.
To quote paleoanthropologist Maria Martinón-Torres of University College London, "researchers should now be looking for a population that lived around 700,000 to 900,000 years ago.”
Without the behavior-what does it matter as otherwise we are no different than any other hominin?
I have to say, as interesting as this may be, I really do not think it matters as whatever our "line" may have been, or how old it may be, it is otherwise no less far removed from fully anatomical and behavioral modern humans as any other species of hominin.
Perhaps, perhaps not. There is evidence that suggests we made some good use of the extra time
Can you give examples? I assume I know what you are reffering to. I would address Blombos cave from a previous thread:
The problem with Blombos cave, supposedly occupied from 100,000-70,000ya and again around 2,000-300ya, is that it is wholly unique-nothing like it found before or after anywhere prior to Eurasia c. 40,000ya. Even the style of tool is extremely similar to a kind not found until 20,000ya in Europe. Beads and bone tools found in the cave aren't convincingly found until after 40,000ya as well yet there they are in Blombos cave completely isolated from the rest of the world for 30,000yrs? Here is the "revolutionary" Blombos "artwork":
A bit of a leap with virtually nothing in between from that to this:
Regardless, Blombos cave is arguably the most out of place discovery in the history of anatomically modern humans as before and after, a time spanning at least 100,000yrs, there is nothing but a veritable wasteland of progress with nothing leading up to it and nothing following it for at least 30,000yrs. Even if this discovery is valid, there is a quantum leap between what is found here and what occurs after 40,000ya with nothing to show for it in between which has hardly anything to do with "climate". There is still a large gap between anatomically modern humans and behaviorally modern humans which despite Blombos cave its beginnings still point to the arrival of Cro-Magnon in Europe c. 40,000ya. Whatever progress was made by the Blombos culture it lived and died with them in that cave. And for what its worth, no bones have yet to be discovered there either.
You are correct that Blombos cave seem to be a place outside of space and time when it comes to the continuous story of human evolution and migrations. We suddenly find signs of fully modern humans just appear there 70,000 years ago (approximately). I tackle this in my book, my argument is that modern humans used watercraft to reach the coast of South Africa from Australasia and/or Southeast Asia. This was a small party of refugees escaping from the devastation caused by the Lake Toba super volcano, 74,000 years ago. The timing fits like a hand in glove, and as we will see in a moment so does the artwork at Blombos.
I was not actually thinking of the Blombos rock and that early art, but instead an almost identical engraving on a shell from Java, dated to over 430,000 years ago and assumed to be produced by Homo erectus, my money is on it being made by early Homo sapiens, but it exists and somebody made it long before that rock in the Blombos cave.
This is interesting, but the dating seems rather up in the air so to say it is in fact much later in reality is unknown. It may well not be, but to be fair it does have a close parallel with the Ngandong hominid of Java (Homo erectus), also controversially given a relatively young date. But what these seem to point to is not necessarily later dates for archaic traits in Homo sapiens, but rather a longer existence of Homo erectus, also quite interesting. Also to be considered is the geography of the Pleistocene in these regions were much different with much more land mass. If the artifacts found on Socotra are in fact Homo erectus (based on nothing more than the period of dating), this means they would have had to have traversed open water which conditions to do so would be even more favorable in the Pleistocene to get to Australia. Then you have the Crete finds dated to 130,000yrs which also suggest crossing open water, though the Mediterranean at the time would have been significantly different as well.
WLH50 has been closely analysed, as have other very archaic looking skulls from Kow Swamp and the morphology is outside the range of Homo erectus they are all a accepted as fully modern human beings. The Kow Swamp skulls are from recent times, some being no more than 10,000 years old.
Hope that all helps, thanks again for getting the debate rolling!