The Journey of Man: A Genetic Odyssey

by Spencer Wells

  When it was later shown that M45 marks the same Y lineage as 92R7, the results made much more sense. Here was our central Asian marker, the same one that gave rise to M173 in Europe. It seems that the central Asian clan had made it to the New World as well, picking up the defining M3 marker in the process. This helped to trace a clear migrational route from Africa to the Middle East to the Americas, via the Eurasian steppes, but it still left us with the problem of how to date the first entry into the Americas. It could have happened any time between 40,000 and 12,000 years ago, taking into account both the genetic and archaeological results.

  A recent analysis of the M45 lineage by Mark Seielstad and myself has defined a further marker, known as M242, which is a descendant of M45. It appears to have arisen in central Asia or southern Siberia around 20,000 years ago, and is distributed across Asia, from southern India to China to Siberia, as well as throughout the Americas. It is found at highest frequency in Siberia, and thus it could be called a Siberian marker. It is also immediately ancestral to M3, and defines an evolutionary order of M45 → M242 → M3 that traces a migration from central Asia to the Americas within the past 20,000 years. M242 appears to be the oldest genetic marker in the Americas. Thus the Y-chromosome results have given us much the same picture of the founding of the Americas as the mtDNA results, but have narrowed down the date of entry considerably. Clearly an entry prior to 20,000 years ago is inconsistent with the genetic results, since M242 was still in central Asia at that time. A more recent migration from Siberia is overwhelmingly likely, consistent with the archaeological evidence.

  The picture that seems to be emerging from the genetic analysis of Native Americans is that of a migration by the Siberian clan from southern to eastern Siberia within the past 20,000 years. This initial move established a population at the north-eastern edge of Asia. Adapted to a hunting life on the central Asian steppes, they would have subsisted almost entirely off of the large mammals of the far north – musk ox, reindeer and mammoth among them. Consummate hunters, with finely crafted microlith tools, portable dwellings and clothing capable of withstanding the intense cold, these well-adapted tundra dwellers would have gradually extended their range eastward. As the ice age moved toward its lowest temperatures, and more moisture became tied up in the ice caps, sea levels would have dropped by over 100 metres. This would have created a land bridge in Beringia, between Siberia and Alaska, of ice-free land formerly submerged in the Bering Sea. The Siberian clan would have been able to move back and forth across this connection, living a dual Asian-American existence.

  Figure 8 M45 is the ancestor of most western Europeans (who have M173) and Native Americans (who have M242 and M3).

  However, these first Americans of 15–20,000 years ago had one more obstacle to overcome. They would almost certainly have been barred from southward expansion by a continuous sheet of ice that covered most of northern Canada and eastern Alaska. It was only as the ice age began to abate, after 15,000 years ago, that it would have become possible to transit the formerly icy interior and enter the North American plains, perhaps via a so-called ‘ice-free corridor’ that some palaeoclimatologists believe ran along the eastern edge of the Rocky mountains. It is around this time that grizzly bears first enter North America from Siberia, showing that humans weren’t the only species to have been stopped by the Alaskan ice. So, the genetic age of 20,000 years, as well as climatological considerations having to do with the extent of glaciation and sea levels, provide an explanation for why we don’t see archaeological remains in the Americas before this time. While archaeologists may someday discover a site that pre-dates 15,000 years ago, the mass of evidence is now in favour of a relatively late initial entry to the Americas. The stones and bones seem to agree with the DNA.

  Manifest destiny

  Interestingly, the Native American genetic data allows us to estimate how many people would have made it into the continent during these first migrations. By looking at the number of chromosomes needed to account for the present distribution of genetic lineages in the Americas, and working out how much diversity would have accumulated over the time that they have been in the continents, it is possible to account for all of the mtDNA and Y-chromosome types in Native Americans with a founding population of around ten or twenty individuals. Because some lineages would have gone extinct during the past 15,000 years, as we saw with our French soup recipes, this is certainly an underestimate of the number of individuals who actually made it across. Perhaps a few dozen, or even a few hundred, actually made the trip. Clearly, though, the diversity present in the Americas is a tiny fraction of that found in Eurasia – which in turn is merely a subset of that found in our African forebears. And of those who made it to Alaska, only a few left descendants. The gene pool of Native Americans carries in it a signal of the hardships faced by their Beringian ancestors thousands of years ago as they moved ever deeper into the deep freeze, scraping a living from the frozen wastes of the far north.

  After they made it through the rigours of life in the freezer, the plains of North America must have seened like the promised land. Here was a vast grassland – much like the steppe they left long ago in central Asia – filled with large grazing animals. It was as though someone who had been adrift on a raft in the ocean for weeks was suddenly transported into a supermarket. The result was a massive increase in population as these highly efficient Siberian hunters took advantage of their newfound good fortune. In just 1,000 years or so they journeyed all the way to the tip of South America, in the process helping to kill off many of the species that made the plains such good hunting grounds. Three-quarters of the large mammals in the Americas were driven to extinction around this time, among them mammoths and horses – the latter weren’t to reappear in the Americas until the Spaniards introduced them in the fifteenth century. While humans may not have done the job on their own – climate change at the end of the last ice age almost certainly played a major role – they probably delivered the coup de grâce to the gentle giants of the plains.

  Counting waves

  One of the most contentious issues in the study of Native American origins is deceptively simple: how many waves of migration were there into the New World? If the earliest Americans came from Siberia, did later migrants arrive from further afield? The 9,500-year-old ‘Caucasoid’ skull recently discovered at Kennewick, in Washington state, hints at ancient connections to Europe. Some anthropologists believe that Australian Aborigines migrated to South America, while others think that the Japanese managed to sail across the Pacific thousands of years ago. Can the genetic data help us to sort through these possibilities and weed out the plausible from the simply barmy?

  Linguistics provides us with one clue. The languages spoken in the Americas – over 600 by some estimates – have long been a contentious issue for linguists. Are they related to each other, or is their diversity simply too great to be subsumed into a few language ‘families’? American linguist Joseph Greenberg, who will play a role in the next chapter, suggested in the 1950s that the vast majority of the languages spoken in the Americas belong to a single language family, which he called Amerind. While this hypothesis has certainly not won universal acceptance, Greenberg has argued his case persuasively, and many scholars are beginning to accept it. Apart from Amerind, which includes all of the languages spoken in South America and most of those spoken in North America, linguists recognize two other language families: Eskimo-Aleut and Na-Dene. Eskimo-Aleut is spoken only in Greenland and the northern parts of Canada, as well as in Alaska and eastern Siberia, while Na-Dene languages are spoken in western Canada and the south-western United States. Do the language families give us a clue about the history of migration to the Americas?

  Greenberg suggested that each family originated with a single migration from Asia to the New World. The speakers of each then spread the languages through the Americas as they migrated, producing the distributions we see today. This model implies that there should be some genetic correlation wi
th the linguistic groups – after all, if it was the movement of people, rather than languages, that caused their spread, then genes should have moved as well. Recent genetic studies have provided support for Greenberg’s classification, suggesting that there were indeed at least two waves of migration originating from different parts of Asia.

  Greenberg thought that the Amerind family was introduced by the earliest migration into the Americas because it is the most widespread, and is the only one spoken in South America. The genetic data bears this out, with Amerind speakers in both North and South America sharing high frequencies of M242 and M3 – marking them as members of the Siberian clan. The mtDNA data obtained by Torroni and Wallace also supports an early Amerind settlement of the Americas. It seems likely that our Beringian hunters were speaking a language that was ancestral to modern Amerind languages, and that 12,000 years of divergence has produced the extraordinary linguistic variety we see today.

  Since Na-Dene was the next most widespread family, Greenberg suggested that it was brought by a second wave of migrants. We do, in fact, see a genetic signal of this later migration. It comes, interestingly, in the form of our Coastal marker, M130. In Na-Dene populations, as many as 25 per cent of men have this marker, while it is found at much lower frequencies in neighbouring northern Amerind speakers. Tellingly, M130 is not found in South America. The genetic dates indicate that it migrated to the Americas within the past 10,000 years, originating in the region of northern China or south-eastern Siberia. By this time the Bering land bridge had been engulfed by the sea once again, so these migrants almost certainly came by boat, migrating along the coast. This is supported by the present distribution of the Na-Dene languages, which are limited to the western half of North America. It seems likely that their ancestors followed the coast all the way around the Pacific Rim, travelling as far as California. The distribution of the Na-Dene languages we see today reflects the continuation of a coastal migration that began in Africa around 50,000 years ago, moving eastward via India to south-east Asia and Australia before heading north towards the Arctic and the Americas. The Coastal marker reveals the deep relationships among the inhabitants of these far-flung places.

  And what about the Eskimo-Aleut speakers? There does not seem to be a distinct genetic signature for this group, and it is likely that it arose as a subset of the M242-bearing Siberian clan, who took on a coastal lifestyle. They migrated to the east, as far as Greenland, using their kayaks to hunt walrus and seal – but their genetic lineages tie them back to their ancestors in Siberia, the tundra-dwelling mammoth hunters of 20,000 years ago.

  As for the other migrations, from Europe or Australia, there is currently no compelling genetic evidence. While M130 would appear to link Na-Dene speaking Native Americans to the Australian Aborigines, the relationship is in fact far deeper, and reflects a common ancestry tens of thousands of years ago in south-east Asia. Likewise for Europeans, who share a common ancestor with most Native Americans, revealed by the high frequency of the central Asian M45 marker in both groups. Furthermore, since Siberians and Upper Palaeolithic Europeans initially came from the same central Asian population, they probably started out looking very similar to each other. Kennewick Man, as a likely descendant of the first migration from Siberia to the New World, may have retained his central Asian features – which could be interpreted as ‘Caucasoid’. In fact, many early American skulls look more European than those of today’s Native Americans, suggesting that their appearance has changed over time. The more ‘Mongoloid’, or east Asian, appearance of modern Native Americans may have originated in the second wave of migration, carrying M130 from east Asia. There is no evidence, however, for an M175-bearing migration of Chinese or Japanese sailors across the Pacific – this marker is simply not found in today’s Native American populations. The genetic evidence is quite clear: all ancient migrants to the Americas seem to have travelled via Siberia.

  Bang

  By 10,000 years ago all of the world’s continents (apart from Antarctica) had been colonized by humans. In just 40,000 years our species had travelled from eastern Africa to Tierra del Fuego, braving deserts, towering mountains and the frozen wastelands of the far north. Their ingenuity had stood them in good stead during this journey, and they had become exquisitely well adapted to life in conditions that were a far cry from their African birthplace. But just as these Upper Palaeolithic wanderers were settling into their new homes, something significant happened. Although it started out as a trivial experiment, it was to change for ever the way that humans interacted with their world. It could be called the second ‘Big Bang’ of human evolution and, like the Great Leap Forward, it would launch another human journey – this one into the realm of recorded history.

  8

  The Importance of Culture

  When the world was first created and the gods were born, each deity had a task in the maintenance of the land. This hard labour led to complaints and demands to find a better solution. One day the water goddess Nammu decided to create man out of clay; Enki and Ninmah were given the task. They drank too much beer and began to play a game where one created beings and the other found a role for them. Three had malformed genitals, and became priests. One was completely unviable, unable to stand or feed itself, and had to be held in Ninmah’s lap – the first human infant.

  Sumerian creation myth

  The Hawaiian archipelago lies in the middle of the Pacific Ocean, over 3,200 km (2,000 miles) from the nearest continental landmass, North America. Today it is one of the major tourist destinations in the United States, with millions visiting its beaches every year. The short flight from California, high-rise hotels and Honolulu traffic belie the isolation of the islands. Today native Hawaiians are a tiny minority in their homeland, but this is a phenomenon of the past hundred years – at one time they were one of the most isolated human populations in the world. And, like the Australians, it is clear that they must have arrived in Hawaii from somewhere else, since there are no other primate species living on the islands. The notion that they voyaged here by boat seems almost unthinkable, yet – like our Oz-bound coastal migrants of 50–60,000 years ago – they must have made the trip.

  When Captain Cook arrived on the island of Kauai in 1778, he was unaware of the ancient voyage the Hawaiians had taken to arrive at this remote spot. He was leading a four-year expedition aboard the Resolution, exploring the north Pacific in an effort to discover the elusive north-west passage between the Atlantic and Pacific Oceans. Cook named the archipelago the Sandwich Islands, after his benefactor the Earl of Sandwich. The native Hawaiians, although interesting as anthropological specimens, were not accepted as equals – and their own name for their native land was ignored.

  Cook noted the primitive character of the people living in Hawaii – in particular, the fact that they were still living in the ‘Stone Age’ and had neither the benefit of metallurgy nor written language. In fact, when he first encountered them, their incredulous reaction to the Resolution’s nautical equipment led him to infer that they had never been aboard a ship. Yet in spite of their apparently primitive way of life, the Hawaiians had made an epic sea journey in order to reach their home. And it was not unique: the nearest inhabited Hawaiian neighbours are the Marquesas Islands, 3,500 km to the south-east, and beyond that there is another 1,500 km of open ocean before reaching the Society Islands, still in the middle of the Pacific Ocean. If Hawaii had been settled by the most direct route of island-hopping, minimizing the distance travelled between each inhabited island, then there would have been at least two enormous sea passages in addition to many other shorter hops. Clearly this was no accident. The Polynesian seafarers who colonized Hawaii were accomplished sailors, able to travel between distant outposts of dry land throughout the Pacific without the benefit of compasses or clocks to infer longitude.

  It is now generally accepted, based on the earliest archaeological evidence for a human presence in Polynesia, that these consummate seafarers made all of their voy
ages within the past 4,000 years. What led them to make the leap into the unknown world of the Pacific? And if humans had been capable of crossing open oceans since at least the time of the first Australians, why did it take them so long to colonize Polynesia? To find the answers to these questions we will have to take a trip back to Eurasia, in search of the factors that led up to the Polynesian odyssey.

  A break with the past

  The Tell el Sultan is 25 km north-east of Jerusalem, on the eastern slope of the Mountains of Judah. The Arabic word tell refers to a mound left by human occupation, and archaeologists have been digging there since the 1870s. Most were looking for evidence to support stories from the Bible, and the uppermost layers in Tell el Sultan do, in fact, belong to the biblical city of Jericho – the name most often used for the site. These later remains, dating from the past 4,000 years, were most carefully scrutinized, but during the course of their work the archaeologists uncovered evidence for earlier occupation. It was only with the focused work of Dame Kathleen Kenyon in the mid-1950s, though, that the earliest layers were systematically explored. What she found there would change our concept of human history.

  Kenyon found evidence for human settlement at Jericho dating from around 10,000 years BC – hunter-gatherer communities that lived off of the game and water resources in much the same way as their Upper Palaeolithic ancestors had 30,000 years before. Then, immediately above this, she found the remains of an early farming community, dating from the period immediately afterwards. The plaster- and shell-decorated skulls she unearthed, evidence of an ancestor-worshipping cult, are some of the best-known artefacts in archaeology. These and other evocative remains made Kenyon one of the most famous archaeologists of her era, but it was the age of the settlements that were to have the greatest effect on the study of prehistory. Up to that time the first known villages had been dated to the fifth millennium BC, while true towns only started to appear 2,000 years later. Using radiocarbon methods, the lowest urban layers at Jericho were dated to around 8500 BC, meaning that this single excavation pushed back the date of the first permanent human settlements by 4,000 years. Kenyon’s excavation of Jericho revealed the earliest evidence in the world for a settled, agrarian society.