The Seven Daughters of Eve (12 page)

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 she 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.

In the early spring of 1992 we set off in two cars, having mapped out a complicated pincer movement whereby two pairs (we were joined by Catherine Irven, who took a week off from another project) would take different routes round the country, meeting up halfway to see how the other was getting on. My car at the time was a thirty-year-old Mk II Jaguar/Daimler that I had bought in a moment of utter madness from a garage fore-court in New Zealand the previous year and had had shipped over. It had a tendency to dislodge its water hoses every so often, causing the coolant to flood out and sending the engine temperature rocketing skywards before eventually conking out. So as well as all the blood sampling equipment on board, I was forced to carry a full toolkit – which was just as well. As we swept into the school in Bala, in central north Wales, there was a loud bang and a foul smell of burning oil filled the car. We pulled up in the car park at one side of the playground and, with the children watching from the classroom windows, I looked under the bonnet to see what had happened this time. There was black oil all over the place and clouds of acrid grey smoke were billowing up from where the oil had hit the exhaust pipes. This wasn't the best way to arrive. I couldn't tackle the job without getting covered in oil; hardly the best way to appear if you want to take blood samples. I shut the bonnet and walked into the school.

Sometimes the problems didn't stop outside. We had let the schools know that we would be happy for them to tell their local papers that we were coming if they wanted to. This had seemed a good idea – until I got to Ysgol-y-Gader in Dolgellau. Sitting with the head teacher, Catherine James, in her office was a reporter from the
Caernarvon and Denbigh Herald
.

‘So you are here to do blood tests on the children?' he asked, opening the interview innocently enough.

‘Well, yes,' I replied. ‘But only as a source of DNA, the genetic material.'

‘Why have you come to Dolgellau?' he asked.

I gave a short description of the background to our project and what we wanted to do. I explained that, because of their settled population over the last few centuries, we were particularly interested in the areas of Wales, like Dolgellau, where the Welsh language was still spoken. He didn't look as if he believed me.

‘You're really here because of the power station, aren't you?' He looked right at me. ‘You want to test the children for mutations, don't you?'

I was stunned. Dolgellau is just twelve miles south of the Trawsfynnyd nuclear reactor. A few months before, news reports had linked mutations found in children living near the nuclear reprocessing plant at Sellafield in Cumbria with their fathers working at the plant. The expression on the head teacher's face rapidly changed from one of mild interest to intense suspicion. Was her school, was she, being used by undercover agents for the nuclear power industry posing as academics engaged on an innocent-sounding study of Celtic genes?

‘Of course not,' I stammered and embarked on a stream of denials and reassurances. I repeated an account of the scientific background, a description of mitochondrial DNA, a summary of our work on ancient bone, and finally what I thought would be an irrefutable certificate of our integrity: ‘Anyway,' I said confidently, ‘I've just come back from doing the same research in the South Pacific.' That would do it. Or so I thought.

‘But isn't that where they test the atom bombs?' he replied, quick as a flash.

I groaned, took a deep breath, and launched myself on another twenty minutes of explanation. Eventually they were both persuaded of our innocence and we could get on.

At the end of my talk to the sixth form, the time came to ask for the blood samples. This was the point where I anticipated some further difficulty. Taking DNA from older schoolchildren (they had to be over sixteen to be able to give legal consent) ruled out taking a large blood sample, and we settled on a drop of blood taken from a finger-prick. This did involve some slight discomfort, and we were worried that no-one would want to do it. At first, to demonstrate how painless it was, I pricked my own finger and dabbed the little drop of blood on to a special absorbent card. Next, the teacher tried it; and one by one the pupils followed. For youngsters who haven't done it before, it does require a little bit of courage. What happened next was an unexpected bonus. Precisely
because
they had done something brave, as soon as they had finished the children shot out of the classroom and round the school – it was the lunch break by then – daring their friends to do the same. A line of suppliants appeared, all swearing they were over sixteen, begging to be sampled not so much because of their intense interest in the project but because they wanted to prove themselves just as courageous as their friends. This wave of bravado spread to the staff room and the kitchens, so that by the start of afternoon classes we had blood samples from all the children old enough to take part, the teachers, the janitors and the dinner ladies.

By the end of the week we had over six hundred blood samples, dried on to cards, from all over Wales – a remarkable haul that far exceeded our expectations. Even though it may not sound a lot, and is only a tiny proportion of the total Welsh population of almost three million, six hundred mitochondrial DNA sequences would be more than enough to get a good idea of the general genetic structure of the principality. Back in the lab we punched out the circles of dried blood from the cards and set about extracting the tiny amount of DNA they contained. Though there are a lot of cells in blood, most of them were no use to us. The red corpuscles, which carry the oxygen and make blood red, are so specialized that they do not need a nucleus or mitochondria; so these superfluous components are evicted early on in the life of the cells, which consequently do not have any DNA in them. Only the white blood cells, whose job it is to seek out and destroy invading bacteria and viruses, retain their own nuclear and mitochondrial DNA. White blood cells make up only 0.1 per cent of the cells in blood, so that while a drop of blood might have fifty million cells in it, only fifty thousand of them contain any DNA. But this is still plenty for the exquisitely sensitive DNA amplification method to work on. We followed the same recipe for getting DNA out of the blood spots as forensic laboratories use on blood-stained clothing prior to taking a genetic fingerprint. This involved boiling the dried blood spots in dilute alkali, which splits the cells open and dissolves the DNA, then adding a resin to absorb the iron which has been leached out from the red blood cells and which would otherwise interfere with the DNA amplification reaction. It worked very well indeed, and before long we had our first 100 Welsh mitochondrial DNA sequences.

Compared to the relative simplicity of the Polynesian sequences, the Welsh results were all over the place. There was no sign of a clear-cut distinction in Wales analogous to what we saw in Polynesia, where the two separate clusters were so clearly the result of a mixture of people from very different origins. It looked as if we had a small number of little clusters which were all quite closely related to each other, rather than two big clusters separated by a large number of mutations. This did not look like the mixture of two very different types of mitochondrial DNA that we would have expected if the people of Wales had a mixed Neanderthal and Cro-Magnon ancestry. If Wales was going to be representative of Europe as a whole, then we were looking at a comparatively recent shared ancestry for everybody.

Along the 500 base segment of the mitochondrial DNA control region, the average distance between any two people among the volunteers from Wales was three mutations. Remembering the rate at which the mitochondrial DNA clock ticks, so that two people with a single mutation between them can be said to have shared a common maternal ancestor about ten thousand years ago, the result from Wales showed that the average length of time it was necessary to go back in the past to connect any two people from Wales was only thirty thousand years; and even the most extreme difference between two of our volunteers, which was eight mutations, meant that they shared a common ancestor only about eighty thousand years ago. Although this is an enormously long time, it is nowhere near long enough for one of them to have been the descendant of a Neanderthal and the other of a Cro-Magnon. Unless the palaeontologists of the replacement school were way off the mark, Neanderthals and Cro-Magnons last shared a common ancestor at least two hundred and fifty thousand years ago. That means that the mitochondrial DNA of a Neanderthal descendant and that of a Cro-Magnon descendant would differ, on average, by at least twenty-five mutations. The biggest difference we saw in Wales was only eight. This was not a mixed population of ancient and modern humans. Either the Welsh were all Neanderthal or they were all Cro-Magnon. But which?