The Journey of Man: A Genetic Odyssey (23 page)

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 with 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.

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.

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 voyages 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.

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.

In the modern world, with its densely populated settlements and reliance on farmed crops and domesticated animals, it is easy to forget that only a few hundred generations ago we were all hunter-gatherers. For most of us, life has changed so completely since the Palaeolithic
that we imagine we have always lived as we do now. In fact, as the deep excavation trenches at Jericho show first-hand, there was a sudden transition from hunting and gathering to settled life around 10,000 years ago. What is particularly fascinating about the timing of this event is that it appears to have happened nearly simultaneously in several independent locations around the world. This suggests that there was a common reason for Upper Palaeolithic people to abandon their nomadic ways and settle into domesticated bliss.

The Middle Eastern culture that immediately preceded the earliest settled, or Neolithic, layers at Jericho belongs to a short-lived cultural tradition known as the Natufian, named after the first site where it was uncovered, Wadi an-Natuf in Israel. The Natufian economy centred on gathering cereal plants – particularly the ancestors of wheat and barley, which were plentiful in the Middle East around this time. It was the end of the last ice age, and the eastern Mediterranean was warming up. The improving climate encouraged the growth of large stands of cereals and nut-bearing trees at higher latitudes than during the ice age, allowing the Natufians to exploit these new resources. By specializing on plentiful species, they were able to settle in one place (near their favoured plants) and still gather enough food to survive.

Middle Eastern archaeologists have found that the end of the last ice age was a period of intense climatic variation in the eastern Mediterranean, with a general pattern of change from a continental to a Mediterranean climate. As archaeologist Brian Fagan summarizes it, this had the effect of producing an ecological zone with long, dry summers and short, wet winters. The effect of this climatic change was to favour grasses, which produce seeds in the spring and then lie dormant over the summer. Early humans would have exploited the relative plenty of food during the spring by harvesting large quantities of seed, then storing it for the rest of the year. This concentrated gathering behaviour would have favoured a settled lifestyle, which set the stage for the revolution that was to follow.