THE PUZZLE OF THE PACIFIC

At nine-fifteen every evening Air New Zealand flight NZI takes off from Los Angeles International Airport. Within thirty seconds it has crossed the short stretch of dry land between the end of the runway and the ocean. There is no throttling back of the engines to cut down on the noise levels. There is no need. Flight NZI is now over the Pacific, and will not see land again until it crosses the Coromandel peninsula on the North Island of New Zealand as it makes its approach to Auckland. But that is still seven thousand miles and fourteen hours ahead. Between then and now there is only the open ocean beneath us – the apparently endless reach of the Pacific Ocean. Sprinkled across this vastness are thousands of islands, but so dwarfed are they by the sea that you are very unlikely to catch even a glimpse of any of them from the plane. And yet, by the time the first European ships began to explore the Pacific, every one of these islands had been found and settled by the people I have come to regard as the greatest maritime explorers the world has ever seen – the Polynesians.

I would like to be able to say that my decision to work in Polynesia was the result of careful planning, of balancing the scientific advantages of studying island populations with the difficulty and expense of working on the other side of the world. I would like to be able to say that, but the truth is that it all came about by accident – literally. In the autumn of 1990 I was taking a term’s sabbatical leave and had arranged to spend part of it at the University of Washington in Seattle and the rest in Melbourne, Australia. This meant crossing the Pacific and, since I had never seen a tropical island before, I scheduled stop-overs in Hawaii and in a place called Rarotonga in the Cook Islands. I had never heard of Rarotonga, and only very vaguely of the Cook Islands for that matter, but it fitted into the flight schedules more conveniently than the better-known alternatives of Tahiti or Fiji.

It also had more by way of contrast to offer. Hawaii is certainly tropical and very beautiful, but at least around the capital, Honolulu, on Oahu there is no doubt at all that you are still very much in America with high-rise, pizza and pet cemeteries. Landing in Rarotonga is a very different cultural experience altogether. There are no luggage carousels: you just pick up your bags from a pile. A man with a guitar is singing a welcoming song as if he means it, which is impressive at four o’clock in the morning. And then there was Malcolm. Cheery and ruddy-faced, Malcolm Laxton-Blinkhorn is English, but nowhere near as grand as his name suggests. He has had what might be called a varied career – marine commando, sheep farmer, actor, television producer…and now hotelier in Rarotonga, having married a local girl. Although his hotel was on the beach at the other side of the island, Rarotonga being only 26 miles round it didn’t take us long to get there. It was still dark, but who could resist going down to the water’s edge and just sitting? Slowly I become aware that it is not as quiet as it should be. There is a distant but persistent low roar, like a busy motorway a mile or two off. But there are virtually no cars on the island and certainly no motorways. The sound I hear is the ocean. As the light grows I can make out a thin white line near the horizon. This is where the swell of the ocean, even on calm days like today, pounds into the coral reef that surrounds and protects the island.

My plan was to spend just a few days on Rarotonga before going on to Melbourne and carrying on with my work. Like most visitors I hired a small motorcycle, took my driving test, which consisted of riding 50 yards up the road and back to the police station, got my driving licence and set off. Straight into a palm tree. I broke my shoulder. I couldn’t leave the island until it had set. Several weeks, I was told. So I settled in for a long stay.

Rarotonga is the main island of the Southern Cooks, a widely scattered archipelago seven hundred miles to the west of Tahiti. The islands get their name from Captain James Cook, the eighteenth-century English navigator, whose portrait (and it always seems to be the same one) is everywhere on the island, even fixing you with his inscrutable gaze as you down a bottle of Cook Islands lager. Though Cook explored many of the islands in the group he inexplicably failed to sight Rarotonga, though it is the largest of the Cooks and rises to 650 metres. The honour of being the first Europeans to land on Rarotonga went to the mutineers of HMS Bounty, who in 1789 stopped on their way to the even more remote Pitcairn Island in their search for a refuge far away from the long arm of the British navy. Today the Cook Islands are internally self-governing, allied with New Zealand in foreign affairs and defence; but they were once a British protectorate and are still a member of the Commonwealth. Even though I doubt whether one in a hundred English people have ever heard of the Cook Islands, the islanders still retain some of the customs of their former colonial patrons. With a lot of time on my hands, and my arm in a sling, I went along to hear a debate in the Cook Islands parliament. The parliament building may only have been a set of corrugated iron roofed huts near the airport runway, but the procedures were every bit as formal as in the House of Commons at Westminster. At the front of the chamber sat the Speaker, through whom all remarks were addressed. Bills were introduced for first readings. Committee stages took place on the floor of the House, and full-scale debates were followed by a division. And guillotine motions. It was getting round to five o’clock in the afternoon when, with a long-winded debate on the pay of MPs and civil servants in full swing, the government introduced a guillotine motion to impose a time limit. And the reason? The cabinet had agreed to sing at the secondary school’s netball team fundraiser at six-thirty, so parliamentary business had to finish by six. This was a place which had obviously got its priorities right.

Figure 3

Another legacy of the past was the museum and library. Even though it was surrounded by coconut palms and mango trees dripping with fruit, once inside I could have been in home counties England: silence, shelves of books and an inconspicuous librarian with a rubber stamp to frank the withdrawals. And empty. There was a substantial collection of books about the Pacific, and I began to read about the part of the world where I was an unplanned (but not too unwilling) prisoner until my fracture healed. Sitting on the fringe of the beach, staring out to the ocean beyond the crashing surf on the reef, knowing that it stretched for thousands of miles in every direction, I found one question persistently nudging me. How did the Polynesians discover and settle this island, and where had they come from?

Captain Cook, though not the first by any means, was by far the most widely travelled of the European navigators who explored the Pacific. Raised in humble circumstances in Yorkshire, and desperate to go to sea as soon as possible, he joined a ship from the port of Whitby. This was a time when an aristocratic pedigree was almost essential for a successful career in the Royal Navy; however, by his sheer brilliance in navigation Cook rose through the ranks to command his own ship. So impressive was he in his navigation of the notorious St Lawrence River during the war against the French in Quebec that he was chosen to take command of HMS Endeavour and lead a scientific party from the Royal Society to observe the transit of Venus across the face of the sun. Timing this rare event was important in the calculation of the distance between the earth and the sun, and the best opportunity for observing the 1769 transit was to be found in Tahiti. This mission accomplished, Cook set out on further explorations of the Pacific which took him, in this and his other two voyages, to New Zealand, Australia, the Pacific north-west coast of America, through the Bering Straits and finally to Hawaii, where he was killed by natives at Kealakekua Bay on the Big Island on Valentine’s Day 1779.

As a navigator, Cook took a professional interest in the question of the origins of the people he encountered on these remote and scattered islands. Over the period of his three voyages he observed the similarities, in both looks and language, between islanders as far apart as Hawaii, Tahiti and New Zealand, and deduced that this meant they all shared a common origin. But where was it? Polynesian tradition too speaks of an ancestral homeland, Havaiiki, but without being specific as to its location. Cook knew only too well that the winds, and the currents, of the Pacific move from east to west across the ocean, from the Americas to Asia. If Polynesians came originally from Asia, then they would have had to battle against both wind and current; if they came from the Americas, they would have been assisted on their voyage by these same natural elements – and these were considerable forces. The Spanish navigators were the first Europeans to explore the Pacific, and they could cross only one way, from east to west. Having sailed from their bases in Central America to the Philippines, they could not sail back the way they had come and had no option but to return by the Great Circle route, north past Japan and Alaska then south down the Pacific seaboard of North America. If Spanish galleons with their formidable sail power and sophisticated navigation could not defeat the winds and currents, then how could the far smaller vessels of the native Polynesians possibly have done so?

One particularly condescending group of western anthropologists were so convinced that the Polynesians were simply too incompetent to organize anything resembling a deliberate voyage of exploration, especially if it meant sailing into the wind, that they felt no further proof of the islanders’ American origin was needed. In their view, the only possible way for these primitives to have reached the islands was by getting lost while out fishing and just drifting on to them – never mind that this would require them to have gone fishing with their whole families, their livestock and a few taro plants stowed on board. This appalling legacy of white colonial attitudes is still keenly felt by many Polynesians. Proof of their Asian origin would certainly crush this nonsense once and for all, and establish their ancestors as supreme masters of the sea.

The controversy in the minds of Europeans surrounding Polynesian origins has lasted for two hundred years. On the one hand, the evidence of archaeology and language, and the types of domesticated animals and plants found in Polynesia, all point to an origin in south-east Asia. On the other, there has been a persistent tradition, most recently revived by the Norwegian anthropologist Thor Heyerdahl, that puts the origin of the first Polynesians in the Americas. Of the evidence for an American connection, the most compelling is the widespread cultivation throughout Polynesia of the kumara or sweet potato, which no-one doubts is native to the Andes of South America. In his books Heyerdahl also provides other connections of language, mythology and some archaeology, like the stone facings on carvings found in Easter Island which bear a striking resemblance to the style of the Incas. But his most celebrated piece of evidence is the voyage of Kon-Tiki, the balsa raft that he used to sail, or rather to drift, from the coast of South America four thousand miles to the Tuamotu islands not far from Tahiti. Of course, to demonstrate that it can be done does not mean that it was done; but Kon-Tiki remains a persuasive argument to a lot of people.

Irritated by what they saw as a stunt by Heyerdahl, the serious anthropologists who had painstakingly pieced together the evidence for an Asian origin did not hide their feelings in their writings. Sitting in the library in Rarotonga, I was shocked by the toxins that dripped from the pages whenever Heyerdahl’s theories were mentioned. His ideas may not have enjoyed wide support among academic anthropologists, but to me, coming fresh and ignorant to the field, his evidence taken at face value seemed to have at least some merit. How strange, I thought, that otherwise moderate and scholarly academics should suddenly lose it when the H-word was mentioned.

I sat in Lucy’s café in Avarua, the capital (indeed, the only town) of Rarotonga, having an ice-cream, just looking at the people coming and going. Did they look more Asian or more American? It wasn’t obvious to me. I distinctly remember one small girl who could have come straight from a National Geographic cover story on the Amazonian rainforests. If only I could test the mitochondrial DNA of the people in the café! I was sure I would be able to tell whether their closest genetic links were with Asia or America. So, at the next hospital appointment to review my fractured shoulder, I explained that I was a geneticist and what I had in mind. Somehow or other I managed to persuade the hospital to let me have the remnants of thirty-five blood samples left over from blood-sugar tests. Diabetes is very common in Rarotonga, and so there are a lot of tests for blood glucose levels. I stored the samples in the freezer back at the hotel. After my shoulder healed – a little too quickly, I thought – I carried these precious phials of blood with me to Australia, where I very nearly had them confiscated by customs, then eventually back to England and my laboratory.

The day after I got back, I unwrapped the samples. There was blood oozing everywhere. The glass tubes had smashed – but fortunately, not all of them. Twenty were still intact, and I got on with sequencing their mitochondrial DNA. Nowadays, DNA sequencing is done automatically in extremely expensive machines, but in the early 1990s it was a manual operation which involved tagging fragments of DNA with mildly radioactive isotopes and separating them in an electric field. There was a point at the end of the long process when the X-ray film which recorded the pattern of radioactive bands that revealed the sequence slowly issued from the developing machine. It was always a tense moment. Will there be a good set of bands? Will there be any bands at all? If the bands are too weak or absent altogether, then something has gone wrong and it’s back to the laboratory bench for another three days.

This time, with the first ten of the twenty samples, everything had worked. Drawn across the X-ray film were four wide columns of dark bands, like bar codes, where the weak radioactivity had blackened the photographic emulsion. The four columns were each divided into ten tracks, one for each sample. Each of the four columns read the sequence of one base, so by putting them together the complete sequence could be worked out. I had arranged it this way, with the ten samples side by side, so that it was easy to see where the differences between individuals were. That was what I really wanted to focus on – the differences between people, rather than the similarities. A straight line across all ten tracks meant that all ten samples were identical at that position; a line with interruptions meant that some samples were different at that position.

In the lab we had sequenced ourselves and a few friends, mostly European, and typically there would be a couple of dozen lines in each batch of ten samples that showed these tell-tale interruptions. When the Rarotongan film came sliding out of the developer there were bands all right, but there was not a single interruption. They were all exactly the same. Had I made a mistake? Had I inadvertently combined the samples somewhere along the line? I needed to develop the second film from samples 11–20 to find out. When this came out it looked at first as if I really had made a mistake. Another whole film of straight lines. But then I saw one track, one individual, that was different from all the rest. Very different. And three other tracks had a single interrupted line. So they hadn’t been mixed. They were real results. I realized at once that they were stunning, and that before very long I would have the answer to the origin of the Polynesians.

Reading through the sequences more carefully and comparing them with the European reference sequence, I saw that the major sequence shared by sixteen of the twenty Polynesians was different at four positions: 189, 217, 247 and 261. The similar sequence shared by three individuals on the second film differed from this only in that they did not have the variant at 247. Otherwise their mitochondrial DNA was identical; they had to be very closely related to the first sixteen. But the twentieth sample was completely different. It had nine variants from the reference sequence along the control region, none of which was shared with the main Rarotongan cluster. Since the blood samples had come from the outpatient clinic in Avarua, there was no guarantee that they were from native Rarotongans, and so I assumed that this unusual sequence was from a tourist or a visitor from another part of the world. Since very few mitochondrial sequences had been published in 1991, there was no telling where on the globe this might be.

I concentrated on the main result – the astonishing similarity of nineteen of the twenty samples. This had to be the mitochondrial DNA of the original Polynesians. All we had to do to solve the Polynesian question was to look in both south-east Asia and South America for comparisons. If we found DNA matches in Chile or Peru, or even in coastal North America, then Heyerdahl was right. If we found them in south-east Asia, he was wrong. If we didn’t find a match in either region, then everyone was wrong. Whichever turned out to be true, one thing was certain: we were going to settle, once and for all, the debate that had raged for over two hundred years. I started to plan my next trip.

You might be asking yourself at this point: ‘Surely if it were as easy as that, blood groups would have given the answer long ago?’ It isn’t as if the blood groups of Polynesia had never been studied; indeed, the first results from Samoa in central Polynesia had been published in 1924, only five years after the Lancet paper by the Herschfelds which first introduced the potential of blood grouping in anthropology. The south Pacific, as I was fast learning, had been a popular place for scientific fieldwork for a long time. However, while they formed a plank in the argument in favour of a south-east Asian origin, decades of work on blood groups and other classical genetic systems had still not produced a definite answer to the puzzle, first because the variations are not definitive, and second because the evolutionary relationships between the types are not known. For example, Polynesians, native South Americans and south-east Asians all have a high frequency of blood group O. Polynesians also have quite a high frequency of blood group A, which is virtually absent in South America. But they also have a low frequency of blood group B, which is quite common in south-east Asia. So what can you make of all that? Which theory do these data support? Advocates of the Asian origin would argue that the extreme rarity of blood group A in native South Americans means that the Polynesian blood group A couldn’t have come from South America. Supporters of the South American case could legitimately respond by saying, as Arthur Mourant suggested in 1976, that the Polynesian blood group A came originally not from Asia but from Europeans through intermarriage over the last three hundred years. And anyway, where’s all the blood group B that should have come from Asia? Add to all this uncertainty the fact that, ultimately, all native Americans trace their origins to Asia through the settlers who crossed the Bering land bridge thousands of years before, and you have a complete mess. Blood group O could have reached Polynesia either directly from Asia or via the Americas. There is no way of knowing. With only three blood group genes – A, B, and O – certainty remains out of reach.

Other classical genetic markers are more variable, none more so than the one that controls the tissue type system important in organ transplantation. Just as blood needs to be cross-matched before a transfusion to avoid a fatal immune reaction, so you must match tissue types between donor and recipient when transplanting organs like heart, kidneys or bone marrow. You don’t hear of people waiting for a blood transfusion because they can’t find a match, but it is a sadly familiar story to hear of patients waiting for months or even years for a suitable heart or kidney donor, often dying before one is found. This is because while there are only four blood groups (A, B, AB and O) there are scores of different tissue types.

I must admit here and now to a serious personal weakness. I have a complete mental block when confronted with the bewildering variety of tissue types. Some of my best friends are cellular immunologists who live, work and breathe tissue types, and the Institute where I work is packed with them. Yet something switches off in my brain when they start describing the various types. All of them begin with the three letters HLA. Then numbers and letters are tacked on to the end: HLA–DRB1, HLA–DPB2, HLA–B27 and so forth. Time and again I go to seminars which kick off with a slide showing a table of this horrendous alphanumeric mélange. For years I concentrated, thinking it would sink in eventually if I tried hard. After all, I have to teach this stuff in my genetics classes. But to no avail. I reluctantly conclude that I am genetically incapable of understanding tissue types beyond knowing that there are an awful lot of them. Which, fortunately, is all you need to know as well. Since there are lots of them, and there are quite a lot of data from Polynesia, South America and south-east Asia, it is relatively easy to track them; and sure enough, most of the tissue type connections are between Polynesia and Asia. But not all. A type called HLA–Bw48 is very rare everywhere except among Polynesians, Inuit and native North Americans. However, though there is certainly plenty of variation, the evolutionary connection between the different types was not known. So, for example, you couldn’t tell whether HLA–Bw48, the type found also in North America, was closely related to other Polynesian types or not. Compare that to the situation with the mitochondrial DNA from Rarotonga. We know that there are three types; we also know that two of them are very closely related to each other, while the third is not. That, as we will see, is an enormous help. We can search other lands not only for the Polynesian mitochondrial types themselves, but for others that are closely related to them as well.

By the time I had planned the return trip, and persuaded the Royal Society to pay for it – after all, they had paid for Cook’s first voyage to Tahiti, as I pointed out in my application – data from native North and South Americans produced by other researchers had begun to circulate. Just as there was one cluster in the Rarotongan sample (if we include the two closely related types in a single cluster and forget about the single sequence from the ‘tourist’), so there were four main clusters in the Americas. Three of these had quite different mitochondrial DNA sequences; the fourth was rather similar to the main Rarotongan sequence of 189, 217, 247, 261, but with variants at positions 189 and 217 only. This looked very interesting. Moreover, both the native American and Rarotongan DNAs shared another unique feature. At the opposite side of the mitochondrial DNA circle from the control region that we had sequenced, a small piece of DNA, only nine bases long, was missing. This definitely increased the chances that the American and Polynesian types were related. Things were looking up for Heyerdahl.

I had heard that in Hawaii Rebecca Cann, one of the authors with Allan Wilson of the original 1987 paper on mitochondrial DNA and human evolution, was studying the DNA of native Hawaiians. This is hard work because, unlike in Rarotonga, there are very few of them left. Two hundred years of immigration, mainly from Asia and America, have reduced the native Hawaiians to a fringe population, many of them living a marginal existence – an all too familiar legacy of colonialism. However, schemes have recently been introduced by which special grants and scholarships are awarded to those who can prove they are of native Hawaiian ancestry. One way of proving this ancestry is through DNA testing; so there was an extra incentive to find out about the mitochondrial genetics of the native Hawaiians.

On my return visit to Rarotonga I arranged to call on Becky Cann in Hawaii, where we sat down in her lab with her postgraduate student, Koji Lum, to compare results. It didn’t take long to discover that we had both found the same major Polynesian type, with the deletion and the same control region variants. This was very exciting, and confirmed the link between the people of Hawaii and those of Rarotonga, three thousand miles to the south. Already I was imagining the enormous ocean distance that separated the two island groups, and the fantastic voyages that must have carried these genes across the sea. Even though it was not unexpected, given the wealth of evidence from the days of Captain Cook onwards that connected all the Polynesians to a common ancestry, just seeing the proof was thrilling. Reluctantly, Becky left to prepare for a seminar, leaving Koji and me in the office sharing our admiration for the voyages of the Polynesians that had carried these genes to Rarotonga and Hawaii.

What followed was one of those rare moments in science when something is revealed that has never been seen before. I was about to pack away my data when I remembered the unusual Rarotongan sequence that I had interpreted as belonging to a tourist and more or less forgotten about. I turned to Koji and asked him if he had ever seen anything like it in native Hawaiians. He agreed to have a look and unpacked his own sheets of results. There was one that stood out from the rest. I laid out my sheet, rather like a roll of wallpaper – this was in the days before laptops – on which the Rarotongan sequences were drawn out, and soon located the unusual sequence. At first Koji’s and my sequences looked completely different; then we realized that we had been reading them from opposite ends. I turned mine around, and began to go through the strange Rarotongan sequence. I read from the left-hand side. The first variant was at position 144.

‘Do you have anything with 144?’ I asked.

‘Yes,’ said Koji.

I carried on four more bases to 148. ‘Anything at 148?’

‘Yes, in the same sample,’ he replied.

I could feel the thrill of discovery tingling up my spine. I carried on. ‘223?’

‘Yes.’

‘241?’

‘Yes.’

I accelerated. ‘293?’

‘Yes.’

‘362?’

‘Yes.’

They were identical. We both looked up at the same time. Our eyes met and two huge, silent smiles shone out from our faces. This was not the DNA of a tourist at all. Discounting the remote possibility that I had accidentally collected a blood sample from a native Hawaiian on holiday in Rarotonga, this had to be a second genuine Polynesian DNA type that had reached into the Pacific as far as the Cook Islands and Hawaii. But where had it come from? It would take another six months to find out.

I flew down to Rarotonga, more determined than ever that we would solve the mystery surrounding the origins of the Polynesians. When I got there, Malcolm, my host from my first visit, arranged for me to meet the man who ran the Prime Minister’s office. In most countries this would be quite impossible, but in Rarotonga it was accomplished at Malcolm’s Christmas party on the beach. It was fortunate that I met Tere Tangiiti and arranged an appointment early on in the proceedings; because my abiding memory of that party was not of making a crucial diplomatic contact, but of the colour blue: the colour of Curaçao which, mixed with champagne, makes the cocktail Blue Lagoon. Blue Lagoon, seafood omelettes and my digestion don’t mix. I was soon to discover the interesting scientific fact that whatever it is they use to colour Curaçao, it is not destroyed in the human stomach. Ten years later I still feel sick at the sight of it.

I needed to get the permission of the cabinet and the co-operation of George Koteka at the health department to collect a substantial DNA sample from Rarotonga and the other islands. I met the cabinet in the Prime Minister’s office above the post office, and they could not have been more helpful. Within a few weeks I had collected five hundred samples from Rarotonga, Atiu, Aitutaki, Mangaia, Pukapuka, Rakahangha, Manihiki and even from the tiny atoll of Palmerston (population sixty-six). I packed them carefully in ice and took them back to Oxford.