The Journey of Man: A Genetic Odyssey (18 page)

The presence of M89 in both north-eastern Africa and the Middle East, and the age of the Upper Palaeolithic archaeological sites in the Levant, helps us to answer the question of whether Eurasia was settled in a single southern coastal emigration from Africa. M130 chromosomes are not found in Africa, suggesting that this coastal marker arose on an M168 chromosome
en route
to Australia. Conversely, M89 Y-chromosomes are not found in Australia or south-east Asia – but they appear at fairly high frequency in north-eastern Africa. The implication is that M89 appeared slightly later than M130, in a population that stayed behind in Africa after the coastal migrants left for Australia. It was these people,
sans
M130 chromosomes, who first colonized the Middle East. There is archaeological evidence for a modern human presence in the Levant from around 45,000 years ago, consistent with the arrival of modern humans from somewhere else. North-eastern Africa is the only nearby location with archaeological
sites dating from around the same time – and, crucially, the same genetic markers we see in the Levant. Thus, the genetic and archaeological patterns tell us that there was a second migration from Africa into the Middle East.

Figure 6 M89 defines the main Y-chromosome lineage in non-Africans.

Once our Upper Palaeolithic migrants had arrived in the Levant, the road into the heart of Eurasia was open. There was a continuous highway of steppe – not unlike African savannah in terms of its species composition – that stretched from the Gulf of Aqaba to northern Iran, and beyond into central Asia and Mongolia. The hurdle of the Sahara having been overcome, the subsequent dispersal of these fully modern humans would have been limited only by their own wanderlust. They had all of the intellectual building blocks that would enable them to conquer the continent, and the process began with gradual migrations along this Steppe Highway, the continental equivalent of the southern Coastal Highway.

At this time, game would have been plentiful. The large, grazing mammals of the steppe zone – particularly antelope and bovids, the ancestors of the domestic cow – would have been easy prey for early humans, and they gradually expanded their range as their numbers
grew. Moving northward and westward, some may have entered the Balkans early on – the first modern humans in Europe. The numbers would not have been great, though, since it was far easier to stay within the bounds of the steppe zone to which they had become so well adapted. The mountains and temperate forests of the Balkan peninsula would have seemed rather alien to early Upper Palaeolithic people, and the genetic data bears this out. Very few Europeans trace their ancestry directly to the Levant of 45,000 years ago, as attested to by the Y-chromosome results. Our canonical Levantine Upper Palaeolithic lineage, M89, is found at frequencies of only a few per cent in western Europe. It may have been these few Middle Eastern immigrants who introduced the earliest signs of the Upper Palaeolithic to Europe, a culture known as the Chattelperronian, but they did not leave a lasting trace. The true conquest of Europe, and the demise of the Mousterian, would have to wait for a later wave of immigration – people with a few more ingredients in their genetic soup.

The main body of Upper Palaeolithic people began to disperse eastward. As with other early human migrations, it almost certainly wasn’t a conscious effort to move from one place to another. Rather, it seems that the continuous belt of steppe stretching across Eurasia provided an easy means of dispersal, gradually following game further and further afield. It was during this time that another marker appeared on the M89 lineage, given the name M9. It was the descendants of M9, a man born perhaps 40,000 years ago on the plains of Iran or southern central Asia, who were to expand their range to the ends of the earth over the next 30,000 years. We will call the people carrying M9 the Eurasian clan.

Figure 7 Descendant lineages of M89 characterizing the main geographic regions in Eurasia.

As the steppe hunters migrated eastward, carrying Eurasian lineages into the interior of the continent, they encountered the most significant geographical bollards so far. These were the great mountain ranges that define the southern central Asian highlands – the Hindu Kush running west to east, the Himalayas running north-west to south-east and the Tien Shan running south-west to north-east. The three ranges
meet in the centre, at the so-called Pamir Knot in present-day Tajikistan, and each radiates off like a spoke in a wheel.

The first humans to see them must have been absolutely awe-inspired. Although they had encountered the Zagros range in western Iran, it was a permeable barrier, with numerous valleys and low passes that would have allowed easy movement. The Zagros themselves actually would have been part of the geographic range of the prey species hunted by Upper Palaeolithic people, with the herds migrating into higher pastures during the summer and descending to the surrounding plains in the winter. The high mountains of central Asia were a different beast altogether. Each of the ranges has peaks that soar to 5,000 metres or higher (in the case of the Tien Shan and Himalayas, over 7,000 metres), and the radiating high-altitude ridges would have been formidable barriers to movement. Remember that the world was in the grip of the last ice age, and temperatures would have been even more extreme than today. It was because of these mountains that our Eurasian migrants would have been split into two groups – one moving to the north of the Hindu Kush, the other to the south, into Pakistan
and the Indian subcontinent. How do we know this? The Y-chromosome again traces the route.

Those who headed north, toward central Asia, had additional mutations on their Eurasian lineage that we will trace below. The Upper Palaeolithic people who headed south, though, had an unrelated mutation on their Y-chromosome known as M20. It is not found at appreciable frequencies outside of India – perhaps 1–2 per cent in some Middle Eastern populations. In the subcontinent, though, around 50 per cent of the men in southern India have M20. This suggests that it marks the earliest significant settlement of India, forming a uniquely Indian genetic substratum – which we can call the Indian clan – that pre-dates later migrations from the north. The ancestors of the Indian clan, who moved into southern India around 30,000 years ago, would have encountered the earlier coastal migrants still living there. From the genetic pattern, it seems likely that any admixture with them was not reciprocal: as we saw in
Chapter 4
, mitochondrial DNA retains strong evidence of the coastal migrants in the form of haplogroup M, while the Y-chromosome primarily shows evidence of later migrants from the north. Thinking back to the scenario we imagined for the birth of the Upper Palaeolithic in Africa, this is the pattern we would expect to see if the invaders took
wives
from the coastal population, but the coastal
men
were largely driven away, killed, or simply not given the chance to reproduce. The result would be the widespread introduction of M mtDNA lineages into the Indian population, while the Coastal Y-chromosome lineages would not be nearly as common – precisely the pattern we see. Today, the frequency of the Coastal marker is only around 5 per cent in southern India, and it falls in frequency as we move northward. This pattern suggests that the contribution from the coastal populations was minimal, at least on the male side. The contrast between the two types of data gives us a glimpse of the behaviour of these first Indians, and hints at a cultural pattern we will explore in more detail in
Chapter 8
.

The migrating Eurasian masses were not only shunted down into India, of course – some of them also migrated to the north of the Hindu Kush, into the heart of central Asia. The Tien Shan would have been an even more formidable barrier than the Hindu Kush, keeping the Upper Palaeolithic hunters out of western China. It is around this
time that another mutation occurred on the Eurasian lineage. It was known as M45, and it will help us to trace two very important later migrations. Using absolute dating methods, we can infer that the M45 mutation occurred approximately 35,000 years ago in central Asia. Today, M45 is found only in central Asians and those who trace their ancestry to this region – thus, it defines a central Asian clan. Descendants of the central Asian clan occur only sporadically in the Middle East and East Asia, and at somewhat higher frequency in India, where the clan appears to have migrated much later (as revealed by the presence of additional mutations). The ‘ancestral’ form – the deepest split in the genealogy of Y-chromosomes from the central Asian clan – is found only in central Asia. This allows us to pinpoint the location of what is effectively a ‘regional Adam’, in much the same way that we identified our African Adam as being an ancestor of the San Bushmen. The deepest branches in the M45 genealogy are found today only in central Asia – not India, or Europe, or east Asia. Thus, M45 arose in central Asia.

The limited distribution of the oldest descendants of the central Asian clan suggests that the population where it arose was isolated from people living in the surrounding parts of the continent. While the Hindu Kush provides a ready explanation for why there was no easy migratory path to India, it is not clear why this population had no contact with groups living in the Middle East. After all, our Eurasian clan had migrated into central Asia along this route – why couldn’t the central Asian clan make the return trip? The inference is that another bollard had entered the story, and given that it hadn’t been an insuperable barrier several thousand years before when the central Asia clan’s ancestors first migrated to the heart of the continent, it was likely to have appeared after that first migration.

Today, the Dasht-e Kavir and Dasht-e Lut deserts of central Iran are scorched, parched wastelands. The tiny population living there ekes out a meagre living using a highly developed system of agriculture, complete with miles of underground irrigation channels known as
ghanats
that have been in use for thousands of years. During the heat of the day the residents of cities such as Yazd retire to subterranean chambers cooled by wind channelled down long pipes, creating a haunting wail that can be heard from miles away. It is inconceivable
that anyone could survive for long in this harsh climate without such a well-adapted lifestyle. Hunting and gathering would be impossible – at least today. Similarly the Karakum and Kyzylkum deserts of central Asia are harsh, desolate places with very few inhabitants apart from a few nomadic shepherds.

There are, however, two belts of continuous steppe across the deserts of central Iran, one to the north of the deserts, near the Caspian, and one to the south, near the Arabian Gulf. When the world was in the midst of its climatic schizophrenia around 40,000 years ago, it is likely that the steppelands and deserts of Iran and central Asia went through periods when the amount of moisture in the atmosphere would have been similar to, or perhaps greater than, today. This could have been aided by changes in the prevailing winds, bringing moisture in off the Arabian Sea. During these relatively wet periods, which may have been brief, humans would have been able to migrate fairly easily across the Iranian plateau and into central Asia – again, the prey and hunting methods would be virtually identical throughout the entire journey. We know that they did so because of the genetic trail they left in their descendants, which traces a direct path from the Levant to central Asia.

Once the ice age reached a threshold temperature, though, there was a significant decrease in precipitation and humidity as evaporation stalled and water became frozen into the expanding ice sheets of the far north. This seems to have happened between 40,000 and 20,000 years ago, and it resulted in the creation of a new desert bollard on our route. The continent was now split into northern, southern and western populations, all headed into the coldest part of the ice age. The people living in India and the Levant had the benefit of the sea, which served to mitigate the effects of the increasingly cold and arid conditions. Those trapped north of the Hindu Kush, however, had to adapt to the increasingly harsh lifestyle of the Eurasian steppes – or die.