Surviving the Ice Age

Although we are the only known surviving species of human on planet Earth today, as recently as during the Last Glacial, which lasted from about 110,000 to 11,000 years ago, there were between three and perhaps five species of fossil human. Neanderthal people held sway in Europe and western Asia from before the Last Glacial till between about 38,000 and 28,000 years ago. They were gradually replaced by anatomically modern humans (AMH), or in the case of Europe the so-called Cro-Magnons. A standard assumption, indeed dogma, has been that the Neanderthals and Cro-Magnons were separate species, but genetic evidence obtained by Svante Pääbo and his team at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, now suggests otherwise. About 4% to 5% of the genes of most living humans outside Africa are Neanderthal in origin. However, such genes are not present in people from south of the Sahara, as Neanderthals never reached those regions. The Neanderthal branch had originally evolved in Europe. For news reports, a short film and a link to the 2010 professional paper in Science on the Neanderthal genome, go to http://www.eva.mpg.de/neandertal/index.html. The characteristics of fair skin, red hair and blue eyes found in some Europeans appear to be derived from Neanderthal ancestors. These characteristics evolved first in Neanderthals, and the most parsimonious interpretation is that the African ancestors of the Cro-Magnons did not have them but their descendants who moved into Europe and interbred with Neanderthals acquired them by intermarriage.

In south-eastern Asia there were two other species of early human present during the Last Glacial. One was the late survival of the last members of the fossil species, Homo erectus, which disappeared perhaps only 50,000 years ago in Java, the very island where their remains had first been found by Eugene Dubois in the late 19th century. As a species Homo erectus lasted for more than 1.6 million years in Africa and Asia, though its presence in Europe has often been a matter for debate. The second south-east Asian species that survived well into if not to the very end of the Last Glacial was the so-called Hobbit, Homo floresiensis, found on the Indonesian island of Flores. The reports on these especially small fossil humans led to an enormous amount of debate and criticism, but on the whole the arguments of the research team led by Mike Morwood and Peter Brown have stood up. These are indeed a different species. Whether there is any connection with Australian Aboriginal stories of little hairy people, we cannot as yet say. Their total extinction is assumed, but in Flores the local people call them ‘Ebu Gogo’ (‘the little grandmother who eats everything’). Given their very short stature (only 1 m tall in adulthood), comparatively large feet (like their namesakes, the Hobbits of Tolkien) and rather special hip and shoulder joints which are much more like those of Australopithecus , the genus of fossil human some 2 to 3 million years ago in Africa that preceded our genus, Homo , they were or are very distinctive. Rather than arguing that these especially small fossil humans are the result of a genetic disorder but otherwise modern, as some critics have done, one perhaps ought to argue that they belong not only in a different species, but a different genus. What is especially thought-provoking is that they survived on Flores till about 11,000 years ago, given that their ancestors would have left Africa more than 1.5 million years ago.

Are the Hobbits in fact extinct? Do they survive anywhere now? So far, there is no scientific evidence that they do. However, before the first publications in 2004 in the eminent British-based science journal, Nature, the species Homo floresiensis was unknown, and stories of little people in Indonesia and Aboriginal Australia were simply taken as legends with no scientific basis. There is a fairly clear description of the Hobbits on one of the web pages of the Australian Museum in Sydney (go to http://australianmuseum.net.au/Homo-floresiensis). My former Honours student, Adam Brumm, who did his PhD at the Australian National University in Canberra, is now leading the team studying the stone tools of Flores, and looking for new sites.

Yet another form of Last Glacial human has been found recently in excavations in Denisova Cave in the Altai Mountains in southern central Siberia by a Russian and German team. It is dated to about 40,000 years ago. Although the number and kind of human bones are still quite limited, DNA analysis suggests that they represent a previously unknown branch of Last Glacial human. Living indigenous peoples in Melanesia, Australia and the remote Pacific islands carry some Denisova genes, but the rest of us by and large do not. The Denisova human has not been given a species or sub-species name yet, so they are simply referred to as Denisovans. ScienceDaily has an up to date, mostly popular account of new work on the Denisovans (http://www.sciencedaily.com/releases/2012/02/120207133602.htm). The entire Denisovan genome has been obtained. This makes it clear they were a sister branch to the Neanderthals, and together with the latter, are our closest relatives in the recent fossil record.

Australia was first colonised by anatomically modern humans or Homo sapiens, more than 50,000 years ago. To reach Australia people had to come by boat or raft, as there was never a landbridge (exposed continental shelf during times of low sea levels) that connected Australia with the expanded lands of south-eastern Asia. This was the first major crossing of open water beyond the sight of land in human evolution. DNA analysis by a Danish-led team (http://www.sciencemag.org/content/334/6052/94) shows evidence that the ancestors of Aboriginal Australians were amongst the first modern peoples to migrate out of Africa and to have reached the south-east Asian / Australian region by between 75,000 and 62,000 years ago. This was before the ancestors of Chinese and European peoples separated from each other. In other words, Aboriginal Australians represent one of the oldest living continuous populations outside of Africa. As pointed out above, whilst moving into or passing through south-east Asia, the Aboriginal ancestors interbred with some members of the Denisovan population.

The Americas on the other hand were first reached later it would seem. As things now stand, it would probably have been sometime between 30,000 and 15,000 years ago when the Bering Landbridge that connected Siberia and Alaska was fully exposed and regularly crossed by reindeer/caribou, mammoth, musk-oxen and other arctic mammals that early Siberians and Alaskans hunted. What human genes were carried to the Americas? Did people actually become isolated from the Old World as has often been claimed? There were probably multiple routes from north-east Asia. Certainly there were at least two through the former lands and islands now referred to as Beringia: a land-based route or routes through central Alaska to the Yukon, and a sea-based route via island-hopping off the southern coast of Beringia and round to the former islands of British Columbia.

During the Last Glacial Africa remained the preserve of anatomically modern humans. The form, abbreviated to AMH, had first evolved in Africa more than 180,000 years ago during the Penultimate Glacial. Ultimately, how much mixing in various directions round the world actually occurred during the Last Glacial, and how many fossil human extinctions really happened in the world at large before the end of the Last Glacial remains uncertain. This is the sort of thing that makes archaeology so exciting. As we learn more and fill in or change certain pictures of the past, we also continue to discover how much we do not know and that we had not expected to find.

My wife Mireille and I have had our mitochondrial DNA (mtDNA) analysed by Oxford Ancestors Ltd, the company that Bryan Sykes, Professor of Human Genetics at the University of Oxford, and his DPhil students founded (http://www.oxfordancestors.com). As some of you will know, we only inherit mtDNA from our mothers, so analysing it provides a record back to whenever on the female side. Male mtDNA is not passed on as during the process of reproduction it is wrapped round the tail of the sperm cell; consequently it falls off as the sperm cell swims, and any possibly remaining bits drop off the successful sperm cell that manages to reach and penetrate the outer wall of the egg. Mireille’s (and her mum’s) mtDNA traces back to the Last Glacial and the district at the top of the Adriatic between what is now Venice and Vienna, at about 25,000 years ago. My maternal mtDNA traces back to the eastern Pyrenees, roughly between Perpignan and Tarascon, at about 22,000 years ago. I have also had my Y-chromosome DNA analysed. This traces my father’s side back to about 26,000 years ago in the area between Vienna and Prague, i.e. central Europe, at the start of the Last Glacial Maximum. In other words, my remote paternal ancestors were neighbours to Mireille’s remote Ice Age maternal ancestors. We will have further, more detailed analyses carried out.

Although it is common in European Palaeolithic (Old Stone Age) studies to assume that there were a number of times in the early antiquity of Europe when it was completely abandoned by early hominins (early fossil humans), with the appearance of Neanderthal people it becomes clear that Europe no longer faced total abandonment. The issue then becomes whether certain parts of Europe were abandoned for thousands of years and then reoccupied by the Neanderthals (e.g. Britain during the Last Interglacial). As anatomically modern humans or Cro-Magnon people spread across Europe during the latter part of the Last Glacial, gradually replacing the Neanderthals during the span of more than 10,000 years, archaeologists studying this process of replacement have extended the concept of partial abandonment of Europe to the Cro-Magnons. It has become orthodox to assume that the North European Plain was effectively completely abandoned during the Last Glacial Maximum some 24,000 to 16,000 years ago, as much of the British Isles, Scandinavia and parts of northern Germany and Poland were under thick ice sheets. Under this scenario regions like Britain and most of Germany had to be recolonised during late glacial times. However, some archaeological and environmental evidence now suggests that abandonment of the North European Plain was neither necessary nor real.

We archaeologists often sit comfortably in our armchairs or at the desk in our study contemplating scenarios for ancient peoples that have little to do with their actual lives. Just because a situation or setting might be inconvenient or unpleasant for us does not mean that ancient people were not able to adapt to new challenges in an environment with which they were already very familiar. The key thing is whether they had sufficient sources of food available.

Another bone of contention in studies of late Ice Age Europe is whether Neanderthals became totally extinct? The school of thought that I would call ‘anti-Neanderthalian’ has held sway in archaeological and anthropological circles for quite a few years. Neanderthals were pushed back into their own species and were seen as extinct. However, as pointed out at the beginning, recent successful reconstruction of the Neanderthal genome shows that living peoples outside Africa carry some 4-5% of their genes as Neanderthal genes.

Still another bone of contention in regard to surviving the European Palaeolithic and the Last Glacial is whether Neolithic farmers moving into Europe from south-western Asia some 8,000 to 6,000 years ago completely or nearly completely replaced the Mesolithic descendants of the Upper Palaeolithic Cro-Magnons. Some years ago the Italian geneticist Luca Cavalli-Sforza argued that this is what had happened, and some archaeologists still accept this scenario. However, recent DNA work shows that many living Europeans in Europe or in former European colonies elsewhere in the present world carry the DNA of people who were fully present in Last Glacial Europe. In short, I should like to argue in favour of an expanded version of the ‘Palaeolithic Continuity Paradigm’ proposed by Mario Alinei, which still needs to be properly challenged and tested, as against simply dismissed (seehttp://www.continuitas.org/intro.html and http://aleximreh.wordpress.com/2011/01/08/paleolithic-continuity-theorymario-alinei-continuitas-group-2/).

I am preparing a new book under contract with Oxford University Press covering all of the above. I hope to submit the manuscript in October 2012. Although the title could change, the working title is Archaeology of Climate Change and Extinction: Surviving the Last Glacial.

one of the oldest Cro-Magnon skull
Caption: One of the oldest Cro-Magnon Skull.LINK