Were multiple early human species living in Georgia, 1.85 million years ago?

New skull with ‘enigmatic’ jawbone and differing tool technologies suggests that two different hominin groups are represented by Dmanisi remains.

The former Soviet republic of Georgia is located at the crossroads of Europe and Asia. Lying on the eastern shores of the Black Sea, it was the destination of Jason and the Argonauts in their quest for the Golden Fleece, but long before this it was a stopping point for the earliest-known hominin migration out of Africa. In 1984, stone tools were discovered at the small medieval town of Dmanisi in the southeast of the country, 93 km (58 miles) southwest of the capital, Tbilisi. Archaeologists broke through the foundations of a medieval building into an ancient river deposit, where simple stone tools resembling those made by the earliest humans were found with the bones of extinct mammals.

During the 1990s, the remains of early humans were recovered, including two partial skulls and a lower jawbone. The fossils were dated by palaeomagnetic, potassium-argon and argon-argon methods, giving an age for the remains of 1.77 million years old (Gabunia, et al., 2000). Subsequent dating of the stone tools indicated that the site was first occupied 1.85 million years ago, and that repeated occupations continued over a period of 80,000 years. There was evidently a long-term human presence in the Caucasus at around or even before the time of the earliest evidence for Homo erectus in Africa (Ferring, et al., 2011).

There have been a number of subsequent discoveries of human remains at the site. These include the skull, lower jawbone and partial skeleton of an adolescent (Vekua, et al., 2002; Lordkipanidze, et al., 2007); the skulls and lower jawbones of two adults (Lordkipanidze, et al., 2006; Lordkipanidze, et al., 2013); and postcranial bones from three other individuals, all adults (Lordkipanidze, et al., 2007). One of the skulls belonged to an elderly male who had lost all but one of his teeth some years prior to his death. He could not have survived unaided and must have been cared for by his companions throughout those last years of his life (Lordkipanidze, et al., 2005; Lordkipanidze, et al., 2006). The other skull, the fifth to be discovered at the site and hence known as Skull 5, is characterised by a large face and thick browridges. Skull 5 is complete and undeformed; it is the only known fully-preserved adult hominin skull from the early Pleistocene (Lordkipanidze, et al., 2013).

From the various remains, body size metrics have been estimated for the Dmanisi hominins. They were 1.45 to 1.66 m (4 ft. 9 in. to 5 ft. 5 in.) tall and weighed 40.0 to 50.0 kg (88 to 110 lb.). The cranial capacities of the five skulls range from 546 to 730 cc, about half that of a modern human. The encephalization quotient (a measure of brain size in relation to body size) lies in the range from 2.4 to 3.13; a figure that is at the lower end of the estimates for African Homo erectus, and is more comparable to that of Homo habilis or Australopithecus (Lordkipanidze, et al., 2007; Lordkipanidze, et al., 2013).

The Dmanisi hominins display a mosaic of primitive and derived (more modern) features. Their limb proportions were similar to those of a modern human. The lower limbs and feet were essentially modern, although the feet turned slightly inwards. On the other hand, the forearm lacked what is known as humeral torsion. In modern humans, the elbow joint is typically rotated relative to the shoulder joint, so that the forearm naturally hangs with the palms facing inwards; but the Dmanisi forearm lacked this rotation, so their palms were oriented more forwards. The inward-turning feet, lack of humeral torsion, small body size and small brain size may be seen as primitive traits, sharing more in common with Homo habilis than with Homo erectus (Lieberman, 2007; Lordkipanidze, et al., 2007).

Initially assigned to African Homo erectus (Vekua, et al., 2002), the Dmanisi hominins were later put forward as a new human species, Homo georgicus (Gabunia, et al., 2002); though this proposal has since been retracted (Lordkipanidze, et al., 2013), and it has been suggested that early African Homo erectus was not only quite widespread, but also unusually variable in both body and brain size, and also less modern than sometimes supposed (Lieberman, 2007).

Two more radical (and diametrically-opposed) possibilities have recently been put forward. The first is that the various species often proposed for early African Homo (Homo habilis, Homo rudolfensis, Homo ergaster and Homo erectus) were all actually variants of the same species, and that early Homo was a single lineage which evolved over time without differentiating into multiple species. This conclusion is based on a claim that shape variation between the five Dmanisi skulls is roughly the same as that seen among the various early Homo skulls from East Africa, even though the former represents a single species and the latter are generally thought to represent several (Lordkipanidze, et al., 2013).

The second proposal (Bermúdez de Castro, et al., 2014) is that Skull 5 represents a different group of early hominins to that of the other Dmanisi remains. The lower jawbone is larger than those of others, and is said to represent a ‘large and somewhat enigmatic individual’. Its shape differs, and the differences cannot be accounted for in terms of body size or sex. It possesses a mosaic of primitive and derived features that are absent from other Dmanisi specimens. Furthermore, patterns of dental wear suggest a higher intake of fibrous and abrasive foods. It has accordingly been suggested that the jawbone is adapted to a different ecological niche to the other Dmanisi hominins, and that it represents a different species.

Although tools document a long-term human presence at Dmanisi, all the actual human remains were found in the same geological layer. This makes the ‘two species’ scenario problematic, as it implies that both species lived at about the same time. However, the stratigraphy of Dmanisi is complex, and it is possible that the fossil remains were re-deposited in the same geological layer after initially occupying sediments of different ages. It has also been claimed that the tools found at Dmanisi are consistent with the existence of two different populations.

More evidence is needed to determine just where the Dmanisi hominins fit into the broader human evolutionary picture, but it is becoming clear that the first hominin dispersal out of Africa was a far more complex process than was at one time supposed.

References:
1. Gabunia, L. et al., Earliest Pleistocene Hominid Cranial Remains from Dmanisi,Republic of Georgia: Taxonomy, Geological Setting, and Age. Science 228, 1019-1025 (2000).

2. Ferring, R. et al., Earliest human occupations at Dmanisi (Georgian Caucasus) dated to 1.85–1.78 Ma. PNAS 108 (26), 10432-10436 (2011).

3. Vekua, A. et al., A New Skull of Early Homo from Dmanisi, Georgia. Science 297, 85-89 (2002).

4. Lordkipanidze, D. et al., Postcranial evidence from early Homo from Dmanisi, Georgia. Nature 449, 305-310 (2007).

5. Lordkipanidze, D. et al., A Fourth Hominin Skull From Dmanisi, Georgia. The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology 288A, 1146–1157 (2006).

6. Lordkipanidze, D. et al., A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo. Science 342, 326-331 (2013).

7. Lordkipanidze, D. et al., The earliest toothless hominin skull. Nature 434, 717-718 (2005).

8. Lieberman, D., Homing in on early Homo. Nature 449, 291-292 (2007).

9. Gabunia, L., de Lumley, M.-A., Vekua, A., Lordkipanidze, D. & de Lumley, H., Découverte d’un nouvel hominidé à Dmanissi (Transcaucasie, Géorgie). C.R. Palévol. 1, 243–253 (2002).

10. Bermúdez de Castro, J., Martinón-Torres, M., Sier, M. & Martín-Francés, L., On the Variability of the Dmanisi Mandibles. PLoS One 9 (2), e88212 (2014).

Bad Science!

While browsing the Independent website yesterday evening I saw this article at the top of the Most Viewed list. An article entitled A skull that that rewrites the history of man is an attention-getter. But when I read the article by Science Editor Steve Connor and this accompanying piece also by Mr Connor I was frankly astounded. The first of the fossil remains in question were discovered near the medieval Georgian town of Dmanisi in 1991 (when Georgia was still a part of the Soviet Union). They were attributed to a new species, Homo georgicus, in a 2002 article in the journal Science (Vekua et al, 2002). Moreover the article is free to download to anybody and does not require a subscription to the journal.

Yet nowhere in either of Mr Connor’s articles does he mention that Homo georgicus has been in the public domain for so long. I’ve read both pretty carefully and they imply that this is a brand new discovery. Furthermore, both the Independent articles are dated 9 September 2009. It does sometimes happen that an old article will feature in a website’s “most viewed” list; this is not the case here.

Turning to the articles themselves, the content leaves a lot to be desired. They are full of phrases such as “conventional view of evolution” and “simple view” which (it is implied) has been overturned by the discovery of the Dmanisi remains. This is utter nonsense. Just about the only thing physical anthropologists ever agree on is to disagree! There is no “simple view” of human evolution that has begun to “unravel”. Rather the view is based on a jigsaw puzzle with pieces that have gradually been added, beginning in the 19th Century with the discovery of the Neanderthals and Java Man.

The “simple view” that Mr Connor alludes to is that Homo habilis evolved from a gracile australopithecine species, possibly A. afrarensis (“Lucy”); Homo erectus evolved from H. habilis and migrated into Eurasia, and that Homo sapiens and the Neanderthals both evolved from Homo erectus via an intermediate form sometimes known as Archaic Homo sapiens. This is a first order approximation that nobody has ever seriously believed represented the true picture.

Homo georgicus is probably an early form of Homo ergaster (“African Homo erectus”). We know that very soon after the appearance of H. ergaster in Africa, Homo erectus shows up in Java. There are two possible interpretations; firstly H. georgicus left Africa and died out, with Asian H. erectus arising from a subsequent migration of H. ergaster from Africa. The second – more likely – possibility is that Homo georgicus carried on into Asia and evolved into Homo erectus. It is more likely because it explains the puzzling absence of the characteristic H. erectus (sensu lato) teardrop-shaped Acheulian handaxes from East Asia. This problem was first noted by the US archaeologist Hallam Movius in 1948. One possible explanation is that the ancestors of the East Asian Homo erectus left Africa before the Acheulian handaxes were invented. This view is supported by the Dmanisi remains, which were found in association with stone tools of the earlier Oldowan type.

Homo georgicus is another piece in the fascinating jigsaw of human evolution, but it doesn’t “rewrite” anything. To suggest otherwise is quite simply bad science and to present a 7 year old article in Science as if it were a new discovery is even worse journalism.

UPDATE:
It appears that I have singled out the Independent unfairly, becuse both the Times and the Guardian also ran the same story. The Times does at least make it clear the discovery happened a while ago, though why three of the UK’s four quality newspapers should choose to report on the Dmanasi hominins now is a complete mystery. It also turns out that the Daily Telegraph ran the same story just under two years ago.

Incredibly even Richard Dawkins website is carrying a link – via Twitter and Fox News – to the Times article. While I am fairly certain Prof. Dawkins is not personally responsible for everything on his site, this is a little surprising! I have to say that I wish Prof. Dawkins – as the country’s leading populariser of science – would devote as much time and energy to combating this kind of “bad science” as he does to opposing creationism, which anybody with a brain larger than Homo georgicus knows is utter nonsense anyway.

UPDATE 16 Sept 2009
It now turns out that David Lordkipanidze, who has headed up the Dmanisi investigation for some years, was speaking to an audience at the British Science Festival in Guildford. No new information was being presented and indeed Prof. Lordkipanidze’s most recent paper on the subject appeared 2 years ago (this was the story carried by the Telegraph in September 2007). The newspapers should really have made these facts clear rather than presenting them as fresh news. Nowhere did I see the words “speaking yesterday at the British Science Festival in Guildford” which would have explained everything.

© Christopher Seddon 2009

References:
Gabunia, L., de Lumley, M.-A., Vekua, A., Lordkipanidze, D., & de Lumley, H. (2002). Découverte d’un nouvel hominidé à Dmanissi (Transcaucasie, Géorgie). C.R. Palévol. , 1, 243–253 .
Gabunia, L., Vekua, A., Lordkipanidze, D., Swisher, C., Ferring, R., Justus, A., et al. (2000). Earliest Pleistocene Hominid Cranial Remains from Dmanisi,Republic of Georgia: Taxonomy, Geological Setting, and Age. Science , 228, 1019-1025.
Klein, R. (2005). Hominin Dispersals in the Old World. In C. Scarre, The Human Past (pp. 84-123).
Lordkipanidze, D., Jashashvili, T., Vekua, A., Ponce de Leon, M., Zollikofer, C., Rightmire, C., et al. (2007). Postcranial evidence from early Homo from Dmanisi, Georgia. Nature , 449, 305-310.
Lordkipanidze, D., Vekua, A., Ferring, R., Rightmire, G., Zollikofer, C., Ponce de León, M., et al. (2006). A Fourth Hominin Skull From Dmanisi, Georgia. The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology , 288A, 1146–1157.
Vekua, A., Lordkipanidze, D., Rightmire, P., Agusti, J., Ferring, R., Maisuradze, G., et al. (2002). A New Skull of Early Homo from Dmanisi, Georgia. Science , 297, 85-89.

Homo georgicus

Homo georgicus is the name proposed to describe fossil human remains that have been found at the medieval town of Dmanisi, Georgia from 1991. The site has been of interest to archaeologists for many years and bones of extinct mammals had previously been recovered from the site. Mode I stone tools, similar to the Oldowan tradition of East Africa, and comprising flakes and flaked pebbles were discovered in 1984. The human remains include four partial human skulls and two lower jaws.

A basalt layer below the fossils has been dated to between 1.95-1.77 million years old by magnetic polarity considerations, which are normal. The material occurring with the fossils shows reversed polarity, dating it from 1.77 million to 790,000 years. The mammal bones do suggest the earlier date based on when certain species overlapped in time.

The skull known as D2700 has an extremely small braincase volume of 600cc, similar to that of Homo habilis and it has been suggested that it has a closer relationship to this species than it does to African Homo ergaster or Asian Homo erectus. If so, it would imply that humans of the habilis rather than the erectus grade were the first to leave Africa. However a recent description of a metatarsal shows a close fit with the derived Homo ergaster body plan rather than that of Homo habilis, which retained many australopithecine features.

References:

Cameron D & Groves C (2004): Bones, Stones and Molecules: “Out of Africa” and Human Origins, Elsevier Academic Press.

Scarre C (2005) (Ed): “The human past”, Thames & Hudson.

Abesalom Vekua, David Lordkipanidze, G. Philip Rightmire, Jordi Agusti, Reid Ferring, Givi Maisuradze, Alexander Mouskhelishvili, Medea Nioradze,
Marcia Ponce de Leon, Martha Tappen, Merab Tvalchrelidze, Christoph Zollikofer (2002): A New Skull of Early Homo from Dmanisi, Georgia, Science 297, 85 (2002).

© Christopher Seddon 2008