by Bryan Sykes
Roger, one of the army of devoted volunteers that are the lifeblood of all archaeological digs, proceeded to make a start on the trench with his trowel. After two weeks he had dug down into the layers of sand, recording the orientation of every artefact he came across. It was slow and painstaking work, not made any easier by the cold, wind and rain. Then, just after lunch on Friday, 13 November 1993, he found a bone – the shin-bone of a very early human. He had uncovered a fragment of Boxgrove Man. And he had saved the dig.
I was shown the bone soon afterwards, and though I am no expert, even I could see how very thick the walls surrounding the central marrow space were, compared to a modern bone. This was the shin-bone of a massive, heavily built human. But was it the bone of an ancestor? This straightforward question goes to the very heart of the controversy over human origins, for one simple reason: whereas every living human (or animal or bird, for that matter) has ancestors, it does not automatically follow that every human fossil had descendants. Boxgrove Man might be an ancestor of twenty-first-century modern humans, or he might belong to a species that is now extinct.
Exactly the same argument surrounds every human fossil. There are many sites of great antiquity in Europe, in Asia and especially in Africa that have yielded what we would have little trouble recognizing as signs of human activity. These are mainly the remnants of shaped stone tools, which obviously survive extremely well. Occasionally, as at Boxgrove, there are animal bones with deliberate cut marks. And very occasionally, there are actual human bones. These fantastically rare and celebrated specimens have been studied and argued over by palaeontologists for decades. Their names – Homo habilis, Homo erectus, Homo heidelbergensis, Homo neanderthalensis – reflect the to and fro of attempts to pigeon-hole them into different species. However, these are species defined on the basis of the anatomical features preserved in the skeletons, particularly the skulls, and not in the biological sense of different, genetically isolated, species who are incapable of breeding with any other. It is an operational classification with no evolutionary consequences. From the shapes of the bones alone there is simply no way of knowing whether humans (I use the term ‘human’ to include everything in the genus Homo) from different parts of the world were capable of successful interbreeding. If they could interbreed, then this opens up the possibility of their exchanging genes and spreading mutations around. They would all be in the same gene pool. But once the different types of human become incapable of interbreeding, they can no longer exchange genes. They become different biological species with isolated gene pools. Their evolutionary pathways are irreversibly separated, setting off in different directions with no turning back. If two or more of these species later come into conflict for space or resources, then, unless a compromise is reached, one species will become extinct.
It is this question that lies behind one of the longest-running and most deep-seated controversies in human evolution. Are the different species defined by palaeontologists – Homo erectus, Homo neanderthalensis and ourselves, Homo sapiens – all part of the same gene pool or not? Or, to put it another way, are modern humans directly descended from the fossils found in their part of the world, or are many of these the remains of now extinct genetically separate human species?
There is no serious doubt that all humans alive today are members of the same species, Homo sapiens. Historical events over the last few hundred years have intermingled people from very different parts of the world, producing abundant evidence of successful interbreeding between all possible combinations. At least, I say that without being completely sure that the opportunity has arisen for absolutely all possible combinations to have been tried; but I’m certain that there would be no genetic barrier to success if they were.
The human fossil record, incomplete and patchy though it is, consistently points to Africa as the ultimate origin of all humans. In Africa and only in Africa is there a sensible progression of fossils covering the past three million years and showing intermediate forms from ape to man. Judging by the fossil record, early humans spent at least another million years in Africa before beginning to venture further afield. Remains in Java and China resemble much older Homo erectus fossils from Africa not only in their general overall physical appearance but also in the types of stone tools found at the sites. Homo erectus was certainly convincingly human, fully upright with a large brain and capable of making and using sophisticated stone tools. But there are no signs of any more primitive, intermediate fossils anywhere outside of Africa. However, while the fossil record is unambiguous in identifying Africa as the cradle of humanity – a conclusion with which very few would nowadays disagree – we should bear in mind some of its limitations. No human fossils have ever been found in west Africa, for example. That does not mean humans were not there until recently; only that the tropical rainforests are not good places to turn into a fossil when you die. No fossils of any of the great apes – gorillas, chimpanzees or orang-utans – have ever been found. As far as the fossil record is concerned, they never existed; and yet we know from the evidence of our own eyes that they did, and do.
Though the fragments of Boxgrove Man and a handful of others are the only glimpses we have of the very earliest European humans, who lived over half a million years ago, the more recent history of Europe is inextricably linked to one dominant form – the Neanderthals. In 1856, workmen quarrying limestone in the Neander valley near Düsseldorf in Germany had just blasted out a small cave and were cleaning away the debris when they came across part of a skull, then thigh-bones, ribs, arm-and shoulder-bones. They thought at first they had come across the remains of an extinct cave bear, an almost routine find in that part of Europe. Only by chance did they happen to mention their discovery to a local schoolteacher and enthusiastic naturalist, Johann Karl Fuhlrott, who realized as soon as he saw the remains that this was no cave bear. Exactly what it was remained controversial for several years. The skull was not that of an ape; but then, with its massive brow ridges, it wasn’t exactly human either. For a start, how old was it?
The Neander valley – in German, Neanderthal – bones were found at a time when the biblical account of the creation was coming under attack from geologists who could not accept that the world was only a few thousand years old. Three years later Charles Darwin published On the Origin of Species and the status of the Genesis story as literal truth started to crumble. Gradually the idea that humans had really ancient predecessors became more widely accepted; and it looked increasingly as though the Neanderthal ‘man’ might be one of them. But this conclusion was reached only after discounting the usual crop of red herrings that accompanies unexpected finds like this. They ranged from the sublime – this was the skull of a man with a mystery bone disease which caused the thickening and the brow ridges – to the ridiculous – it was the skeleton of a Cossack horseman who had been injured in the Napoleonic Wars and crawled into the cave to die. Without his sword and uniform…?
Over the next hundred years, several other fossils were found that conformed to the same pattern: heavy build; large braincase (actually slightly larger than the modern average), presumably to accommodate a large brain; no real chin; a prominent nose; and those distinct, heavy brow ridges. The fossils came from Gibraltar and southern Spain – in fact, the first Gibraltar specimen had been excavated in 1848, eight years before the discovery at Neanderthal, but was neglected. They were found in Belgium, France, Croatia; and from further afield in Israel, Iraq and as far east as Uzbekistan. The stone tools found at Neanderthal sites were more advanced than those associated with their predecessors, though not a great deal. They may have intentionally buried their dead and even cared for the sick and dying. These were not the unreconstructed brutes of popular imagination. But still the question remained: were these people the ancestors of modern Europeans or just another evolutionary dead end?
The same question applies to other parts of the world. Are modern Chinese the descendants of the people whose million-year-old remains were found at
Zhoukoudian near Beijing? Did the ancient people of Ngandong in Java eventually become the modern native Australians and Papuans? That is certainly the view of an influential and vocal school of contemporary physical anthropologists – the multi-regionalists. They see the change in human physical characteristics over the past million years from the robust, heavy-boned ancestors to their slender (at least theoretically!) and light-boned descendants as a gradual process of adaptation happening at different speeds in different parts of the world. Though geographically remote from each other, there has been enough contact among these groups to maintain a common gene pool and allow modern Homo sapiens to breed successfully with whomever he or she wishes. Always assuming they get the chance.
The opposite camp – the replacement school – fiercely contests this view of continuity. Their view is that both the Neanderthal and the Zhoukoudian and Ngandong fossils, also known as Peking and Java man, are remnants of extinct human species that were replaced by a much more recent expansion of Homo sapiens out of Africa. The fossil evidence put forward in support of this contention is the abrupt appearance in Europe about forty-five thousand years ago of humans with much lighter skeletons and skulls which are virtually indistinguishable from those of modern Europeans. There is no debate, even among the most argumentative of palaeontologists, that these are the remains of our own species, Homo sapiens. In Europe, these early examples are known as the Cro-Magnons, named (in the same tradition as the Neanderthals) after the cave site of Cro-Magnon in France: one of the places where, in 1868, such bones were first found. It is inconceivable, according to the replacement school, that a mutation of such magnitude could have occurred as to transform the heavily built Neanderthals into the thoroughly modern-looking Cro-Magnon more or less (in evolutionary time) overnight. The archaeological as opposed to the fossil evidence for an abrupt replacement of Neanderthals by Cro-Magnons is the use of a much more highly developed and delicately crafted set of tools, with flint slivers used for knives, scrapers and engravers; the appearance for the very first time of animal bone and antler as an industrial material; and one more crucial ingredient – art.
The Cro-Magnons had invented representational art. Over two hundred caves in France and northern Spain are adorned with their strangely beautiful and vigorous images of wild animals. Deer and horses, mammoths and bison decorate the walls of the deepest caverns, far from the light of day. These are not crude or child-like drawings but the expression of a mature and accomplished imagery, an abstracted and mystical representation of their world.
Is it possible that the Neanderthals had not only transformed their physical appearance and their technology, but had also become artists as well? The multi-regionalists think just that, and, indeed, see in some remains and stone tools evidence of the intermediate forms you would expect from a gradual transition. But there are no precedents for the cave art anywhere in the lands where Neanderthals have been found. The school of sudden replacement traces the modern anatomy and the improved technology back to Africa, to sites like Omo-Kibish in Ethiopia, which are well over a hundred thousand years old. Even so, although anatomically modern skulls have been found along the trail to Europe in the Near East, principally at Qafzeh and Skhul in Israel, there was no sign there of art.
Without new evidence from a completely different and independent source, genetics, the debate about whether native Europeans were descended from Neanderthals or from the apparently distinct later arrivals, the Cro-Magnons, would have rumbled on unresolved. In all fields of human endeavour where there is a shortage of objective evidence, opinions and people inevitably become polarized into rival camps. Once entrenched, the occupants will not be dislodged; they would rather die than change their minds. Such was the situation when we set out to apply our powerful genetic tools to the conundrum; so we knew the path ahead would likely lead us into a minefield.
9
THE LAST OF THE NEANDERTHALS
Genetics is at its most powerful when it comes to distinguishing between rival theories. In the Pacific it had come down decisively on the side of an Asian origin for the Polynesians at the expense of Thor Heyerdahl’s American alternative. Could it do the same for Europe? Could genetics give an equally clear answer to the true fate of the Neanderthals? Were these strange humans a staging post on the way to fully modern Europeans, or were they an essentially different species that was replaced by the lighter-boned, technologically advanced and artistic new arrivals from Africa? This was the principal question I now set out to answer with mitochondrial DNA. Just as the success with the Syrian hamster had given me the confidence in the reliability of the DNA segment known as the control region, so its brilliant performance in the Pacific meant I now felt ready to disentangle the far greater complexities of Europe.
I had discovered the true origins of the Polynesians by studying the genetic variety we found in their modern descendants. The great majority had DNA signatures that were either identical, or very similar to one another. Along the whole 500 base DNA segment that we had routinely sequenced, there was a difference of only one, or at most two, mutations among them. On an evolutionary timescale, these people had all shared a common ancestor very recently indeed. The genetic trail of identical and near-identical sequences led back from island to island, to Taiwan and south China. This is a beautifully laid out record of the incredible voyages of the first Polynesians, easily read in the genes of the modern population. But there are a few Polynesians, around 4 per cent, whose DNA tells a different story. They are closely related to one another within a cluster of sequences but, on average, thirteen mutations distant from the main Polynesian sequences. This cluster did not come from mainland Asia but – as described in chapter 7 – could be traced back to the coast of New Guinea, from where they, or maybe just she, boarded a Lapita canoe and headed east into the Pacific.
The mitochondrial DNA had shown very clearly that the maternal ancestors of modern Polynesians came from two different places – from two very different peoples, who had since become mixed. Would the Europeans also show a clearly mixed genetic ancestry with, perhaps, a ‘Neanderthal’ cluster and a ‘Cro-Magnon’ cluster to be found among the modern population? Even though the mixing of Neanderthal and Cro-Magnon genes could have been going on for forty or fifty thousand years, compared to only three or four thousand years in the Pacific, I felt sure that I would still be able to pick out any distinct clusters in Europe, just as I had in Polynesia. That I felt so confident was entirely thanks to the special inheritance pattern of mitochondrial DNA. Unlike the chromosomes of the nucleus, mitochondrial DNA is not shuffled at each generation. The only changes are brought about by mutation, and forty thousand years is not so very long in mutational time. If there had been substantial interbreeding between the Neanderthals and the Cro-Magnons, we would find the evidence in the modern population.
There was only one way to find out: my research team had to start testing, and on a wide scale. What was going to be the best way of going about it? Whom would we ask, and how? And what would we ask for – a blood sample? There were plenty of questions to be resolved, but one thing I was sure of. If at all possible, we would collect the samples ourselves, rather than relying on older collections. The scientific reason for this was that I wanted to be sure we knew that if a sample came from, say, north Wales, it was from someone whose ancestors came from the same area. We sat down to plan our campaign. Martin Richards, now the senior scientist on the team, thought of approaching local family history societies; but I wasn’t sure this route would give us wide enough coverage in a short enough time. Our research grant only had another year to run, and we would need to build a persuasive case, built on results, to gain continued funding for the project. I favoured touring sheep and cattle markets, reasoning that farmers were likely to be the most settled population with local roots going back a long way. But it was Kate Smalley, the third member of the team, who came up with the solution.
Kate had been a teacher before coming into research, and s
he thought that if we wrote to schools who taught biology in the sixth form we could combine a presentation on modern genetics with a sample collection. This idea had a lot going for it. Kate thought we would get a high uptake if we contacted schools with this suggestion, not just because genetics was beginning to feature more and more in the examination syllabus, but also because it gave the teachers themselves a double period off. She was absolutely right and we had a 100% favourable response from the schools we approached.
Where were we to start? We would need to home in on areas where we could be sure of finding a high proportion of long-established local families. I had been reading some old papers written in the 1950s about blood groups in Wales. One anecdote in particular caught my eye. It was an account of the odd head shapes allegedly found in mid-Wales. Those were the days, thankfully long gone, when skull measurements were a respected source of information for physical anthropologists intent on classifying the whole of humanity into different racial types. According to this account, the heads of some people in mid-Wales bore a close resemblance to those of ‘Stone-Age Man’, whatever that was. Apparently a hat shop in the market town of Llandysul, not far from Cardigan, regularly had to supply hats made to measure because so many of their customers were unable to fit into the standard sizes. This is not the sort of thing to take too seriously; but neither should it be totally dismissed out of hand. After all, it was skull measurements that initially led Arthur Mourant to turn his attention to the Basques when looking for the descendants of Europe’s ‘original’ population. So Wales looked like a good place to start, and within a month Kate had organized a week-long tour of the whole principality.