An iconic early human skull

The earliest known human fossils outside of Africa were found at a site near Dmanisi in Georgia, between 1991 and 2005, following the discovery there in 1984 of primitive stone tools together with early Pleistocene animal bones. The Dmanisi finds occur with those of sabre-toothed cats and giant cheetahs, and so are probably not interments or in some kind of dwelling but were probably dragged into an underground carnivore den.

The five Dmanisi skulls of Homo erectus georgicus (credits; M.S. Ponce de Leon & P.E. Zollkofer, University of Zurich)

The five Dmanisi skulls of Homo erectus georgicus (credits; M.S. Ponce de Leon & P.E. Zollkofer, University of Zurich)

Initially the remains were assigned to a new species – Homo georgicus – but are now believed to be a subspecies of H. erectus. The finds are anatomically rich, with fossils of at least 5 individuals, both male and female, including 5 well-preserved skulls.  Analysing them has been a long process. Details of the best preserved, indeed the most complete early Homo skull ever found, have taken 8 years since its discovery in 2005 to reach publication (Lordkipanidze, D.  et al. 2013. A complete skull from Dmanisi, Georgia, and the evolutionary biology of early Homo. Science, v. 342, p. 326-331, DOI: 10.1126/science.1238484).

To the surprise of palaeoanthropologists, this specimen of Homo erectus georgicus has some ape-like features, including a protruding upper jaw in a relatively large face that most resembles the oldest African H. habilis, from Ethiopia, dated at 2.3 Ma. With a braincase of 546 cm3, the skull is on the small side of H. habilis and in the range of late australopithecines. Yet, like the much younger Homo floresiensis – dubbed ‘the Hobbit’ – the association with tools, of the most basic Oldowan type,  places it a cut above non-human hominins. The rest of the skeletal fossils show individuals with modern human proportions, albeit somewhat diminutive.

Surprises multiplied when comparative studies of all 5 skulls were complete. They are so different that, if found in widely separated specimens, would be placed in different species by most anatomists. Ruling out the chance association of several human species far from their Africa origins – few would suggest that up to 5 species left Africa at the same time and stuck together – a suggested explanation is that they represent a population of a human lineage in the process of evolving to a new species. The strength of this hypothesis contradicts the other recent view that several human species may have cohabited environments at different times. It also seems to throw into question the adoption of the name H. erectus for later human populations in both Africa and Eurasia: unless, as the authors tentatively suggest, there was genetic continuity and connectivity over large distances between both evolving populations

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5 responses to “An iconic early human skull

  1. I love the comical picture created in the final paragraph of five species of ancient humans marching arm-in-arm, side-by-side out of Africa to pioneer the Old World! Could it be that the fossils were not all laid down simultaneously and over a longer timespan than previously assumed? And even though the variation in cranial shape might be compatible with that seen in modern humans and chimpanzees, in neither (as far as I am aware) do you see such morphological variation in any one place at any one time… Can the Dmanisi skulls really all belong to a genetically-viable population?

    • Thanks for your comment Jamie. I don’t think the 5 skulls do represent 5 species, and nor do the finders, but more likely members of one species that was polymorphic. Or maybe one that was on the cusp of a change. Impossible to tell without DNA – I wonder if Svante Paabo’s team is analysing them as we speak.

      Steve Drury

      • Not a problem, it’s a stimulating topic that should capture the imagination of all given that these played a role in our evolution!

        I’m just amazed at the degree of variation present in the five skulls. I wonder if the interpretations would have been different if “Skull 5” had been discovered first..?

        • To me, Jamie, the big problem with hominin evolution is around what constitutes a species once a being appears that consciously changes its environment and especially uses part of the environment to effect the changes – ie tools. Increasingly, culture and consciousness would seem to bear more and more on what constitutes Darwinian fitness and thereby on natural selection. That is, an individual who would be physiologically ‘unfit’ but for his/her consciousness, culture and social links can survive to reproduce successfully. Among a great any other things that could lead to polymorphism among genetically related individuals. But I am not an evolutionary biologist… You might be interested by what I wrote on a different, independent blog at http://peopleandnature.wordpress.com/article-store/no-morals-really-are-not-written-in-our-genes/

          • The transmission of culture and social links sounds a little like the concept of memes to me, or am I barking up the wrong tree? The replication of ideas…

            Your point about the concept of a species is also pertinent. Some would say humans are unique in our manipulation and exploitation of our environment but primates and birds are also known to use tools of sorts. Thanks for the link, I’ll get round to reading it in due course!

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