Lumping at Dmanisi

Palaeontologists at Dmanisi, an increasingly famous village in Georgia, have made some quite interesting discoveries: a small collection of early Homo skeletons from people living in the same place at the same time that are nevertheless fairly variable in appearance, as exemplified by the recently-described “skull 5.” The usual rules of population dynamics say that you can’t have different species that have the same niche (i.e. they have same shtick – they live in the same way, eat the same food etc) living in the same place – one of them will quickly win out and exclude the others. If this hasn’t happened – and it doesn’t seem to have at Dmanisi – we must conclude that the organisms are or were of the same species.

The variation at Dmanisi really is quite large for one small site: it’s about the same as in modern, living humans, or in living chimpanzees. Indeed, the core implication of the findings that everyone was been talking about in October is that the early Homo species from around 1.5 to 2 million years ago – Homo erectus, H. habilis, H. ergaster, and H. rudolfensis – can all be lumped into H. erectus. They still exist, but they would no-longer be classed as their own separate species.

Creationist responses, as documented at the Panda’s Thumb by Jim Foley, have been interesting if seemingly poorly-informed. One reason why their opinion on this specific story might be amusing comes from their attempts to divide human ancestors into solidly-delineated “human” and “not human” camps. This is of course impossible to do – hence why they tend to disagree with each other so often – but a common dividing line used is to say that the genus Homo is definitely and completely human, and that the genus Australopithecus is completely not. Usually added to this litmus test, however, is the claim that Homo habilis isn’t actually a human and is really an australopithecine that has been promoted to Homo by evolutionists to shore up their evolutionary progression. Take a look back at the species I listed that should be folded into one: this study has the side-effect of uniting fossils that many creationists consider ape and human into the same species. Despite this being pointed out, e.g. by Foley, I’ve yet to see a creationist notice this curious paradox.

Joining the pile of obliviousness a little late comes Brian Thomas and Frank Sherwin in Human-like Fossil Menagerie Stuns Scientists. Their article actually cites approvingly a 1975 piece by Duane Gish that makes the Homo habilis claim I just mentioned, yet they still don’t realise the problem – presumably they never actually read the Gish article. They seem to think that the recent Science paper that came to the single-species conclusion was saying that the Dmanisi skulls, and the early Homo ex-species are really the same as modern (“fully”) humans:

Yale University anthropologist Andrew Hill, who was not involved in the discovery, told the Wall Street Journal, “‘It gives you a chance to look at variation for the first time.'” Instead of showing different transitional human forms living at different times and leading up to modern humans, the fossilized remains at this site showed variation occurring at the same time. Assuming the remains were all human, as the Science authors did, these results end up “drastically simplifying the story of human evolution,” according to the WSJ.

It means that there are fewer true side branches, but not that human evolution didn’t happen. As the paper says: (emphasis added, square brackets original)

When seen from the Dmanisi perspective, morphological diversity in the African fossil Homo record around 1.8 Ma probably reflects variation between demes of a single evolving lineage, which is appropriately named H. erectus. The hypothesis of multiple independent lineages (paleospecies) (15, 31) appears less parsimonious, especially in the absence of empirical evidence for adaptation to separate ecological niches. The hypothesis of phyletic evolution within a single but polymorphic lineage raises a classificatory but not evolutionary dilemma, and it is premature to describe the rate(s) of evolution in this lineage, given the small available samples. Specimens previously attributed to H. ergaster are thus sensibly classified as a chronosubspecies, H. erectus ergaster. The Dmanisi population probably originated from an Early Pleistocene expansion of the H. erectus lineage from Africa, so it is sensibly placed within H. e. ergaster and formally designated as H. e. e. georgicus to denote the geographic location of this deme [thus retracting the species status given earlier to mandible D2600 (12)].

Also, there’s the matter of the figure from the paper that’s been circulating along with it:

This graph plots skull morphology of various fossils and living organisms, with shape face on the x axis and brain size on the y. As for the points, here’s what Adam Benton had to say in his article:

A comparison of chimps, humans and fossil humans. Chimps are squares, humans circles and the numbers are the Dmanisi skulls. Note how the variation between chimps is no greater than the variation in the Dmanisi skeletons

Crucially for us, however, is that while the Dmanisi skulls may occupy the same sized area as modern humans or chimps, it is a different area – they are not the same as modern humans, but occupy their own space in the middle between humans and chimps. A smattering of other fossils that belong to no clear grouping show that all three groups – humans, chimps, and early Homo skulls – are inseparably connected, in a further blow to creationists.

The most important, and most misguided paragraph by Thomas/Sherwin is this one:

Among those species [that would have to be “wiped from the textbooks”] would be Neandertal and Cro-Magnon, which deserve no recognition as separate forms that supposedly evolved into Homo sapiens—modern humans. They were uniquely formed people living at the same time as modern-looking people. Australopithecus is also out of the evolutionary line up, now that evolutionists have finally followed its fossil evidence to where creation scientists did long ago when they concluded that it was just an extinct ape and had clearly never evolved into humans. Without these key players, the popular pageant of human evolution truly should all be wiped from the textbooks.

The first sentence is part of the quest by the ICR to make Neanderthals “fully human,” which is in no way supported by this study. For one, it concerned hominids living about a million years earlier, and for two the degree of lumping is around the same level of variation as in modern humans – Neanderthals were outside of that. “Cro-Magnon,” meanwhile, doesn’t actually describe anything in a scientific sense, and seems to be only used in the way they just did by people who want to make it clear that their knowledge of human evolution comes straight from the 19th century. The Australopithecus line is so far detached from the actual conclusions of this study that even Sherwin and Thomas cannot possibly believe it. Allow me to present one of my amazing hastily-drawn diagrams:

This, very broadly speaking, is the family tree of humans as presently known. The implications of this new paper do not touch this in any way, except that the stuff within the blue dotted line is all considered part of the same species. They still exist, they’re still connected to the rest, they’re still not the same as us, but they just get classified differently.

Thomas and Sherwin conclude:

If the Dmanisi fossils represent ancient humans, then they show that generations of experts in human evolution have spent effort, time, and research dollars arranging fossil fragments of human skulls into an evolutionary line of descent that never really existed. Perhaps it is time to rethink the whole story.

No, it’s not. What it’s time for are new people to write these articles for the ICR. Basic competency in understanding and explaining the conclusions of scientific papers would be nice, but anything is better than nothing.