Friday, 18 October 2013

Evolution in Georgia

Image: Guram Bumbiashvili, Georgian National Museum
Complete skull of 1.8-million-year-old hominin found - life - 17 October 2013 - New Scientist

We have a great example of how science handles new evidence and differing opinion in today's New Scientist. Contrast this to the way religions handle disagreement.

A 1.8 million year-old hominid skull is causing scientists to ask some fundamental questions about the widely accepted model for the human evolutionary tree, going right back to the ape-like australopithecines of East and South Africa and especially the East African group of what are thought to be a contemporaneous group of closely related members of the Homo genus, including one which is on our direct line of descent, H. erectus.

According to the standard model, it was in this East African group that the human brain began to become significantly larger than in the more ape-like australopithecus group. This in turn drove a diversification into three or more different species, H. erectus, H. rudolfensis and H. habilis all living in the same area at the same time. H. erectus later evolved into H. heidelbergensis which then spread out of Africa in the first wave of Homo radiation, giving rise to Neanderthals in Europe, Denisovans in Asia and possibly a third as yet unidentified species, and maybe H. florensis - the so-called 'hobbit'. Meanwhile, the H. heidelbergensis who remained in Africa evolved into modern H. sapiens, some of whom came out of Africa in one or more waves, interbred with Neanderthals and Denisovans to form a brief Homo ring complex in Euro-Asia before we exterminated the earlier species.

Now this has all been called into question by a team led by David Lordkipanidze of the Georgian National Museum in Tbilisi who has examined this very well-preserved and complete skull which was recovered from a site at Dmanisi in Georgia, south of the Caucasus Mountains and formerly part of the Soviet Union. This is the fifth, and best preserved hominid skull to be found at Dmanisi which can't realistically be thought of as from different species, and already these skulls have revealed far more variability than we normally expect.

And that begs the question, if H. erectus displayed such a wide variability in Asia, why would we not expect it to have done in East Africa? So, are these assumed three or more different contemporaneous species in East Africa in fact different species, or just normal variations of H. erectus?

What now happens is that some people will come in with tentative opinions, some will question the findings which raise the questions and some will take a neutral stance, pointing out that we still need a lot more information and that all conclusions are provisional.

For example:

We are not against the idea that there might have been multiple species 2 million years ago, but we don't have sufficient fossil evidence to make the distinctions between species.

Christoph Zollikofer, The Anthropological Institute and Museum in Zurich, Switzerland

The specimens from Dmanisi are all H. erectus and the species was variable, but I don't believe all the African fossils belong to H. erectus. Lordkipanidze's analysis suggests even the much more ape-like hominins in the genus Australopithecus belong to the H. erectus group. It is not surprising, then, that the new analysis misses the more subtle shape differences between Homo species.

Fred Spoor, The Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany (paraphrased)

I think they will be proved right that some of those early African fossils can reasonably join a variable H. erectus species, but Africa is a huge continent with a deep record of the earliest stages of human evolution, and there certainly seems to have been species-level diversity there prior to 2 million years ago. So I still doubt that all of the 'early Homo' fossils can reasonably be lumped into an evolving H. erectus lineage.

Chris Stringer, The Natural History Museum in London, UK

And that's about as acrimonious as it gets, because everyone recognises that what is important is not that your favourite notion wins but that the truth is eventually arrived at. Truth is the prize we are all seeking.

What a contrast between that and the way religions do it. Fortunately, we've managed to civilise most religions now so they can no longer settle these sorts of disputes with mass slaughter, burnings at the stake or by taking away the livelihood of anyone who dares to disagree or raise a voice of doubt or worse still, question the authority of the church and the privileges of the clerics. If only they weren't overwhelmed by the sheer volume of printed matter disagreeing with them nowadays, they would still be banning, burning and censoring books and scientific opinion too. Only a few hundred years ago publications like the New Scientist would very likely have been banned and the editor, together with the authors of papers such as this one on human evolution would have been prevented from publishing or working in their chosen professions even if they had been lucky enough not to be called before a clerical court, fighting for their lives against a charge of heresy.

A Complete Skull from Dmanisi, Georgia, and the Evolutionary Biology of Early Homo
David Lordkipanidze, Marcia S. Ponce de León, Ann Margvelashvili, Yoel Rak, G. Philip Rightmire, Abesalom Vekua, and Christoph P. E. Zollikofer
Science 18 October 2013: 342 (6156), 326-331. [DOI:10.1126/science.1238484]

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