by Bryan Sykes
As soon as I smelled the burning, I pulled across the suction line. This was a device rather like a miniature vacuum cleaner which I had rigged up for collecting the powdered dentine into a sterile test tube. With this in place, I began to drill out the dentine, carefully moving the bit up and down inside the tooth, pulling back as soon as I felt it touch the hard enamel on the other side. All the time the vacuum line was transferring the creamy white powder into the test tube and collecting it in a small pile at the bottom. Within a few minutes, I had completely excavated the inside of the tooth. In the test tube lay precisely 208 milligrams of dentine powder from the Old Stone Age.
Within two weeks, and in ways that we will cover later, I had recovered enough DNA from the Cheddar tooth to read the genetic fingerprint of its original owner – a young man whose pattern of life was so utterly different from our own that it is hard to imagine any possible connection between him and ourselves. And yet the fragment of his DNA that I had recovered from his tooth is exactly the same in every detail as that of thousands of people living in the Isles today. His descendants are with us still – and you may well be one of them.
It is now almost ten years since the day I drilled into the Cheddar tooth, but the moment is still vivid in my memory. It was not the first time I had attempted to recover DNA from ancient skeletons, but it was the most scary. This was a priceless and irreplaceable specimen. But what was I, a trained geneticist, doing drilling into the tooth in the first place? I had spent the early part of my career researching the causes of inherited diseases, mainly those affecting the skeleton – hence the location of my laboratory in Oxford’s Institute of Molecular Medicine. This research had led to the discovery of the genes involved in giving strength to bones – the genes which coded for bone collagen – and to the mutations in the collagen genes which caused these often devastating diseases.
It was only a chance introduction to an archaeologist, Robert Hedges, who runs the carbon-dating lab in Oxford, that got me involved in the human past at all. Robert wanted to see if he could get more from the bone samples coming to his laboratory for carbon-dating than merely finding out how old they were. Carbon-dating relies on counting the tiny number of radioactive carbon atoms that lie in the collagen of ancient organic remains. As these atoms decay with time, the fewer there are, the older the sample. Robert got in touch, having heard about my research on the genetics of bone collagen, and we started to plan what we might be able to do with these old bones. To cut a long story short, within two years we had worked out a way of recovering DNA from human and animal bones that were hundreds or even thousands of years old.
Being the first laboratory in the world to do this, we were well placed to receive exciting samples from all over the world. Over the years we have had bits of Neanderthals; Oetzi, the famous Iceman from the Alps; various claimants to being Anastasia, the last of the Romanovs; a selection of dead poets and statesmen; not to mention the odd piece of Yeti skin. To put the DNA results from this eclectic collection into some form of context, I began a programme of collecting DNA samples from living people. For instance, although it was wonderful to be able to get DNA from the 5,000-year-old Iceman, and that became a story in itself, it only became really interesting when his DNA could be compared, and indeed matched, with someone living today. The whereabouts of his modern descendants told us something about the movement of people throughout Europe during the five millennia since his death.
Sometimes the DNA from modern people can solve long-standing riddles that had proved to be intractable by any other means. The outstanding example of this was the research on the origin of the Polynesians. These are the people who live on the far-flung islands of the Pacific. All the islands, from Hawaii in the north to Easter Island in the east and New Zealand in the far south, had been settled by Polynesians well before the time Europeans began to explore the Pacific Ocean in the early part of the sixteenth century. But where had the Polynesians come from? Was it from Asia, as the bulk of the evidence from language, domestic animals and crops suggested? Or had they arrived in the other direction from America, as the legendary Norwegian anthropologist Thor Heyerdahl believed? Like many schoolboys, I had been captivated by Heyerdahl’s adventures on the balsa raft Kon-Tiki, on which he drifted from Peru to the Tuamotu islands, not far from Tahiti, to prove his point. So it was with a tinge of regret that, in 1995, I published the genetic data which proved conclusively that Heyerdahl was wrong. The Polynesians had come from Asia, not America. This slight regret at having disproved a boyhood hero was more than compensated by the proof that the Polynesians must have explored the Pacific intentionally, driving their canoes into wind and current eastwards across the vast ocean, rather than lazily drifting with the prevailing elements from South America. The ancestors of today’s Polynesians were without doubt the greatest maritime explorers the world has ever known.
The proof of their true origins came from the DNA of modern Polynesians that I had collected from dozens of Pacific islands. From the detailed genetic fingerprints of the islanders I was able to trace the route that their resolute ancestors had taken through the island chains of South-east Asia and out into the vast Pacific Ocean. In ways that I will explain later, I could follow the genetic threads that had percolated through the generations and reconstruct the 3,000-year-old journeys of these astonishing navigators.
It was because I was attempting to reproduce this first success in the much more difficult arena of Europe that I found myself drilling into the Cheddar tooth. My colleagues and I had followed the same procedure that had yielded such compelling results in Polynesia. We had collected almost 1,000 DNA samples from all over Europe and, again in ways I will later explain, come to a conclusion about the origin of modern Europeans. That conclusion was, in a nutshell, that the ancestors of most native Europeans were hunter-gatherers and not, as was commonly believed at the time, farmers who had spread into Europe from the Middle East about 8,500 years ago. To say that our conclusion caused a stir is an understatement. There followed several years of fierce debate between ourselves and the proponents of the agricultural-ancestry theory, and the experiment with the Cheddar tooth was one of our efforts to prove our case. The idea behind it was that, if we could show that a very old human fossil, a genuine hunter-gatherer who lived well before farming arrived, had pretty much the same DNA as people living today, that would strengthen our side of the argument.
The fact that the Cheddar tooth DNA was identical to modern Europeans’ had several ramifications. This was the DNA of a man who, without any doubt, was a hunter-gatherer who had lived at least 6,000 years before farming reached the Isles. Taken with all the other genetic evidence, the result helped to swing opinion towards a predominantly hunter-gatherer ancestry for Europeans and away from the prevalent theory of a great wave of ancient farmers sweeping out from the Middle East and overwhelming the thinly spread hunters. The heat has gone out of that particular debate by now, and I think it is fair to say that most people today think that the impact of migrating farmers on the genetic make-up of Europe was far less than previously thought.
A few months after finding the DNA from the 12,000-year-old Cheddar tooth I got permission to repeat the process with a younger specimen from the same cave. This was the famous ‘Cheddar Man’. His remains had been excavated in 1903 and, like the other skeleton, had been stored in the Natural History Museum in South Kensington. They had been carbon-dated to about 9,000 years ago, still well before the arrival of farming in Britain and so still relevant to the hunter/farmer debate. Sure enough, after drilling out the tooth and analysing the DNA from the dentine powder, I could see that Cheddar Man’s DNA was also thoroughly modern. It was not the same, in detail, as the earlier Cheddar tooth, but it did match quite a few modern Britons’, one of whom lived just down the road from the Caves. A local television company had got wind of our work on the Cheddar fossils and, between us, we had dreamed up a format whereby, in parallel to the work on Cheddar Man’s teeth, we would also
test the DNA of the pupils at the local school. If we could find a DNA match between Cheddar Man and a modern-day nearby resident it would be a good local-interest story as well as a neat demonstration of genetic continuity.
With all the DNA results in from the school, and from Cheddar Man himself, the producer arranged a notorious ‘reveal’ session. The pupils, all aged between sixteen and eighteen, and the master who had organized the event at the school, gathered in the hall, nervously waiting for the results to be announced. The camera passed across the faces of the teenagers, each one apprehensive that it might be their DNA that had been matched to Cheddar Man. The presenter spoke, the match was revealed and the cameras swivelled round to bring one face into tight close-up. It was not one of the pupils at all, but the history teacher who had made the arrangements – Mr Adrian Targett. Gasps all round, a blushing teacher and a score of ever so slightly disappointed teenagers.
The following day Adrian Targett’s smiling face was on the front page of every national newspaper. He was pictured crouching next to the replica of Cheddar Man’s skeleton at the spot in the cave where it had been discovered in 1903. Even the tabloids carried the story, impressively assembling a topless model in a skimpy rabbit-skin loincloth and with a hastily assembled flint axe. Adrian told me later that he had been offered a ‘five-figure sum’ to appear in a loincloth but had, sensibly, declined. The following day the story was picked up by newspapers abroad. It proved to be particularly popular in the US, probably because it fitted in nicely with the image of a bucolic English countryside in which it takes 9,000 years for someone’s descendants to move 300 yards down the road. People still remember the story even now, and when I was lecturing in California last year I was introduced by the organizers as the man who got DNA from the Cheese Man.
The Cheddar Men, though they lived a very long time ago, were not the first human inhabitants of the Isles. There are scattered shreds of evidence that the Isles were once occupied by archaic species of humans, not directly ancestral to our own species, Homo sapiens. A shin bone from Boxgrove Quarry near Chichester on the Sussex coast, a tooth from Pontnewydd Cave in north Wales, both over a quarter of a million years old and both the remains, as far as can be told, of much sturdier, large-boned humans, more like Neanderthals than our own species. The recent discovery of flint tools that have been exposed in a crumbling cliff near Lowestoft on the Suffolk coast is evidence, albeit indirect, of a human presence on the Isles more than half a million years ago. Fascinating though these finds are, they are merely glimpses into the world of long-extinct humans who came and went but left no lasting impression on the Isles, small bands of roving hunters whose luck finally ran out. These were not our ancestors.
The earliest evidence of our own species, Homo sapiens, in the Isles comes from Paviland Cave just above the rocky shoreline of the Gower Peninsula to the west of Swansea in South Wales. In 1823 the Oxford palaeontologist William Buckland excavated the partial skeleton of a man. Misled by the presence of ivory ornaments near the body, Buckland assumed that he had found the remains of a woman and, because the bones were stained with red ochre as part of an unknown burial ritual, she soon became known as ‘the Red Lady of Paviland’. However, a more thorough analysis of the bones, particularly the pelvis, showed that the Red Lady was actually a man, though he still retains the title. When Buckland found these bones they were so well preserved that he thought they could not be all that old. His theory was that they were the remains of a woman who had been living in the cave while working at a nearby Roman camp. But he was wrong again. We now know from carbon-dating that the Red Lady was much older than the time of the Roman occupation. ‘She’ died 26,000 years ago and ‘her’ pendant was not made of elephant ivory but had been carved from the tusk of a mammoth. We know, from the deliberate burial, that the Red Lady was survived by her relatives, but no trace of them remains. After the time of the Red Lady, there is a long empty gap in the fossil record of the Isles. There is nothing until the time of the ‘older’ of the Cheddar Men, just over 12,000 years ago. Why the break? There is one very simple answer – the Ice Age.
About 24,000 years ago the temperatures in the northern latitudes around the globe, including the Isles, began to drop as the planet entered once again into the downward phase of a glacial cycle. These regular cycles of bitter cold and comparative mildness have been going on for at least 2 million years. They are caused by the slight shifts in the way the earth rotates and moves in its orbit around the sun. The shape of the orbit changes from circular to elliptical and then back to circular about once every 96,000 years. The angle of the earth’s axis changes, shifting the positions of the Arctic Circle and the Tropic of Cancer up and down by 3 degrees of latitude, and several hundred miles, once every 42,000 years. Another cycle, every 20,000 years, alters the seasons when the earth is at different parts of its orbit. As the earth runs through this cycle, the signs of the zodiac slowly move round and we enter new astrological ‘ages’, the latest being Aquarius. The combination of all three cycles one on top of the other means the earth’s climate never stands still for long. The effect is to change the amount of sunlight which hits the higher latitudes in both hemispheres, slowly increasing and decreasing as the overlapping cycles gradually shift the planet’s position with respect to the sun. We are now in a warm phase of the long-term glacial cycle, but it will not last for ever and at some as yet unpredictable time in the future we will slide inexorably into another Ice Age. How soon the next cold phase will begin and to what extent its chilling effects will be tempered by ‘global warming’ are all uncertainties for future generations.
For the descendants of the Red Lady and the other scattered occupants of the Isles 24,000 years ago, even though they did not know it, their tenancy of the land was coming to an end. Gradually the year-on-year temperatures began to fall. Snow that covered the mountains in winter no longer melted in the summer and gradually built up into a permanent ice cap. The sea began to recede as more and more water became locked in permanent ice sheets, not just in the Isles but also at the Poles and over the mountain ranges of Europe, Asia and America. The Isles became a peninsula as the North Sea receded. Britain and Ireland were joined. Vicious winds howled around the edges of the expanding ice cap as the weather systems shifted away from the succession of moisture-bearing Atlantic depressions towards an Arctic climate of intense, dry cold. And all the time, the ice moved south. The herds of migrating game – reindeer, bison, wild horse and mammoth – moved their ranges away from the worsening conditions, and the scattered groups of humans who depended on them for food had no choice but to follow them. By the time of the coldest phase of the Ice Age, 18,000 years ago, there were no humans left in Britain, or anywhere else in Europe north of the Alps.
The descendants of the Red Lady and their contemporaries had retreated to refuges in southern France, Italy and Spain, abandoning northern Europe to the frost and ice. Great glaciers flowed downhill from the ice domes over the mountains of northern Britain, gouging out steep-sided valleys and pulverizing the bedrock as they ground their way across the landscape, obliterating everything in their path. All evidence of human occupation in northern Britain was completely erased by the ice. Only south of a line from the English Midlands to central Ireland, which marked the edge of the ice, could any trace remain.
And then, quite suddenly, the climate began to improve as the planet moved its alignment in the heavens. The warmth of the sun returned to the northern latitudes and the ice began to melt. Our ancestors followed the herds north from their huddled refuges as the frozen land began to thaw. Carbon-dating of charcoal left by campfires has traced the advancing front and by 13,000 years ago they had reached northern France. A millennium later, the older of the Cheddar Men, or his immediate ancestors, were among the first to arrive in the Isles, by foot across the land that now lies beneath the North Sea. His are among the oldest remains to be found anywhere in post-Ice Age Britain. He arrived in a landscape scrubbed clean of human occupation b
y the effects of the Ice Age, even though the ice itself never reached as far south as his home in Cheddar. His camp in the gorge was perfect as an ambush site to trap the migrating herds of reindeer as they moved from their summer feeding grounds on the high Mendips to spend the winter on the Somerset Levels. Remains at the site showed he was skilled at making the variety of flint tools on which the life of the hunter depended.
When he arrived, 12,000 years or so ago, the Isles were connected to each other and to the rest of continental Europe. The sea was 100 feet lower than it is now and large tracts of land that are now under water were well above sea level. Ireland was connected to mainland Britain through a broad plain that joined it to the west coast of Scotland and took in what is now the whisky isle of Islay. The Irish Sea, which now entirely separates Ireland from the rest of the Isles, was then a narrow sea inlet between flat plains, blocked at its northern end by the isthmus that joined Scotland to the north of Ireland. The Western Isles off the north-west coast of Scotland were similarly joined to the mainland with a narrow strip of dry land. The Hebridean islands of Skye, Mull, Rum, Coll and Tiree were not islands then; neither were the Orkney Islands, now separated from the far north of the Scottish mainland by the turbulent seas of the Pentland Firth. Only the Shetland Isles, 60 miles north of Orkney, were truly islands in those far-off days.