The Seven Daughters of Eve (18 page)

‘The genetic legacy of Paleolithic
Homo sapiens
in extant Europeans: a Y-chromosome perspective' was the culmination of a large collaboration between scientists from Italy, eastern Europe and the United States. I had been asked to comment on the paper by the BBC on the day it was published, and had a copy faxed through to the Royal Society in London where I was at a scientific meeting. As soon as the fax arrived I took it into one of the drawing rooms which overlooked St James's Park and sat down. My heart sank as I went through the long list of authors at the beginning of the paper. There, second from the end, was the name L. Luca Cavalli-Sforza. After all the battles of the previous four years, I could hardly expect my old adversary to agree with me at last.

Reading through the article, I could see that it was constructed along generally similar lines to our mitochondrial paper of 1996. They had fingerprinted the Y-chromosomes of 1,007 males from twenty-five European and Middle Eastern locations. Then, just as we had, they had drawn an evolutionary framework and identified clusters. They discovered ten Y-chromosome clusters rather than the seven that we had found with mitochondria. Then they had estimated the ages of these clusters, as we had done, from the accumulated mutations within each one. I turned the pages with growing excitement. What were the ages of these clusters going to be? Would they be mostly in the Palaeolithic, like six of the seven mitochondrial clusters? Or would they be much more recent, in the time of the Neolithic and the early farmers? I certainly knew what I expected the paper to say, given Luca's prominent position as an author and his well-known views on the magnitude of the genetic impact of agriculture. The paper was full of dense statistics but there, on the penultimate page, my eye went straight to the vital paragraph. It began: ‘Analyses of mitochondrial DNA sequence variation in European populations have been conducted,' and it referenced our 1996 paper. ‘These data suggested', it continued, ‘that the gene pool has about 80% Palaeolithic and 20% Neolithic ancestry.' That was fair. I read on to the next sentence, expecting it to begin the demolition of our position. But, it did not. Instead, I read the words: ‘Our data support this conclusion.'

I couldn't believe it. The tension drained from my body. The battle was over. We had been put through the wringer for four and a half years. We had endured the panics about the mutation rate being wrong, about mitochondrial recombination messing everything up, and about the control region being completely unreliable. And now it was over. Mitochondrial DNA and the Y-chromosome told the same story. The history of men tallied with the history of women. Luca and I could finally agree. It had been a tough battle, but a fair one. The Neolithic farmers had certainly been important; but they had only contributed about one fifth of our genes. It was the hunters of the Palaeolithic that had created the main body of the modern European gene pool.

From the remains in Cheddar Gorge we had extracted direct proof of the genetic continuity between people living today and the hunters of the Upper Palaeolithic. We now knew that this unbroken thread, accurately and faithfully recorded in our DNA, stretched back beyond the beginnings of history, beyond the ages of iron, bronze and copper to an ancient world of ice, forest and tundra. Only the exceedingly slow beat of the molecular clock separated the DNA we found in Cheddar Man from the DNA in our two utterly modern descendants Adrian Targett and Cuthbert the butler. The evolutionary reconstruction we had done on the DNA from thousands of living Europeans had pointed us to that conclusion, and eventually we had found physical evidence to validate it. Now we also had the crucial endorsement from another genetic system altogether, the Y-chromosome, of the assertion that our genetic roots do indeed go back deep into the Palaeolithic.

Our reconstructions had identified seven major genetic clusters among the Europeans. Within each of these clusters, the DNA sequences were either identical or very similar to one another. Over 95 per cent of modern-day native Europeans fit into one or other of these seven groups. Our interpretation of European prehistory and the emphasis it placed on the Palaeolithic hunter–gatherers had depended on giving ages to these clusters, and we had worked these out by averaging the number of mutations we found in all the modern members of the seven different clans. This gave us a measure of how many times the molecular clock had chimed within each clan. Knowing the rate at which the clock ticked, we could then work out how old each clan really was. Old clusters had accumulated more changes over the millennia. The molecular clock, slow as it is, would have struck more often. Young clusters, on the other hand, would not have had as much time to accumulate as many changes, and the DNA sequences of people within a young cluster would be more alike.

The seven clusters had ages of between 45,000 and 10,000 years. What these estimates actually tell us is the length of time it has taken for all the mutations that we see within a cluster to have arisen from a single founder sequence. And, by purely logical deduction, the inescapable but breathtaking conclusion is that the single founder sequence at the root of each of the seven clusters was carried by
just one woman
in each case. So the ages we had given to each of the clusters became the times in the past when these seven women, the clan mothers, actually lived. It required only that I gave them names to bring them to life and to arouse in me, and everyone who has heard about them, an intense curiosity about their lives. Ursula, Xenia, Helena, Velda, Tara, Katrine and Jasmine became real people. I chose names that began with the letter by which the clusters had been known since we had adopted Antonio Torroni's alphabetic classification system. Ursula was the clan mother of cluster U. Cluster H had Helena at its root. Jasmine was the common ancestor for cluster J; and so on. These were no longer theoretical concepts, obscured by statistics and computer algorithms; they were now real women. But what were they like, these women to whom almost everyone in Europe is connected by an unbroken, almost umbilical thread reaching back into the deep past?

There are a few qualifications you needed to be a clan mother. The first is that you needed to have daughters. That is obvious, because the gene we are following, mitochondrial DNA, is passed from mother to daughter. A woman who had only sons could not be a clan mother because her children would never pass on the mitochondrial DNA they received from her. So that is the first rule. The second is that you had to have at least
two
daughters. It's easiest to see why by looking at things the other way round, from the present to the past. The clan mother is the
most recent
maternal ancestor that all the members of a clan have in common. Imagine a clan with ten million living members and imagine that we knew perfectly from the registry of births, marriages and deaths exactly how they are all related. As we went back in time, generation by generation, we would see the maternal lines slowly joining up. The lines in brothers and sisters would converge, after just one generation, in their mother. After two generations, cousins would converge on their maternal grandmother, their mother's mother. Three generations ago it would be the second cousins whose lines coalesced in their maternal great-grandmothers. And so on. At each generation there would be fewer and fewer people in the clan who had maternal descendants living today. Eventually, hundreds or even thousands of generations ago, there would be only two women in the clan who could claim to have maternal descendants living in the twenty-first century. Further back still, the maternal lines of these two women would converge on a single woman – the true clan mother. And to be in that position she must have had not one but
two
daughters.

Figure 5

To clarify this rather tricky point take a look at Figure 5. I have drawn out an imaginary maternal genealogy of fifteen living women, represented by the white circles on the right-hand side. Only the ancestor marked by the arrow is the
most recent
common ancestor of all fifteen. Her mother is also a maternal ancestor of all the women, but she is not the most recent. Her daughter is. Equally,
her
two daughters, marked with asterisks, are both maternal ancestors of living women, but neither daughter is the maternal ancestor of all fifteen of them. If we called this a clan, then only the woman with the arrow is the clan mother. Exactly the same principle applies whether there are fifteen people in a clan, or fifteen thousand or fifteen million. There is still only one clan mother.

A clan mother did not have to be the only woman around at the time and she certainly wouldn't have been. But she is the only one who is connected through this unbroken maternal thread right through to the present day. Her contemporaries, many of whom will themselves have had daughters and grand-daughters, are not clan mothers because at some point between then and now their descendants in the female line either had no children or produced only sons. The lines died out. Of course, since we do not have records going back more than a few hundred years, let alone a few thousand, we can never hope to know the precise genealogy all the way back to the clan mother. All we can do is use the DNA sequences and the slow ticking of the molecular clock to reconstruct the main events as mutations slowly appear in these maternal lines. Even though we can never arrive at a perfect reconstruction of the true genealogy, this does not detract from the logical inevitability of there being only one mother for each clan. That conclusion is inescapable.

What remain open to debate are the exact times and places that these seven women lived. I have made my best estimates of the times by summing the mutations that have accumulated in each of the seven clans. The locations I have chosen for the seven women, again my best estimates, are distilled from the present-day geographical distribution of the clans and their different branches.

Generally speaking, the likely geographical origin for a clan is not necessarily the place where it is most common today but the place where it is the most varied. For example, going back to the Pacific, the clan that is very common in Polynesia did not originate there. Even though it is extremely abundant, there is very little diversity within the clan in Polynesia: most Polynesians who are in that clan today have the same DNA sequence. On genetic grounds alone, the origin of the clan is much more likely to be further west in the islands of Indonesia around the Moluccas. Even though the clan is not particularly common on the Moluccas today, there is a lot more variation within it there than in Polynesia. Only a fraction of the population moved out to Polynesia, so the diversity within the clan drops. In native Taiwanese, the diversity within the clan is even higher although, as in the Moluccas, it is not especially common. That makes it likely that Taiwan is an even earlier origin of the Polynesian clan than the Moluccas. When it comes to Europe, although we lose the simplicity that comes through dealing with discrete island populations, the same considerations apply. Clan origins are likely to be near the locations where they are the most variable today. Even so, this somewhat theoretical argument has to be tempered with realism. The mother of a clan which is twenty thousand years old cannot have lived in the north of Scotland, even if that might be where the clan is most varied today, for the very practical reason that Scotland was covered in ice at the time. I freely admit that there is a considerable element of uncertainty about exactly where these women lived. Indeed, while I would be alarmed if an equal uncertainty surrounded the exacting science behind the genetics, I somehow feel an element of mystery surrounding certain aspects of these seven individuals is not inappropriate.

As I became more engrossed in these seven women, I began to imagine what existence was really like for them. I was filled with an intense curiosity about their lives. Having let the genetics direct me to the times and places where the seven clan mothers most likely lived, I drew on well-established archaeological and climatic records to inform myself about them. The record of past temperatures is held in the frozen cores taken from the polar ice caps. Raised and submerged beaches mark out the sea-level changes which have been such a feature of the past fifty thousand years. The vegetation leaves its mark in pollen which survives for thousands of years after it was shed by the flower that made it. The changing styles of tools made from stone and bone that are excavated from sites of human habitation record the ebb and flow of technological progress. The animal and fish bones that litter the same sites tell of our ancestors' diet. All these pieces of tangible evidence combine with the genetics to recreate the imagined lives of these seven women, Ursula, Xenia, Helena, Velda, Tara, Katrine and Jasmine. They were real people, genetically almost identical to us, their descendants, but living in very different circumstances. What lives they must have led.

Come with me now on a journey into the deep past. Guided by the unbroken genetic threads that link us to our ancestors, we can travel back to a time before the dawn of history, to a world of ice and snow, of bare mountains and endless plains, to meet these remarkable women – the Seven Daughters of Eve.