Out of Eden: The Peopling of the World (10 page)

Another kind of dissent was shown by traditional population geneticists. They were surprised and perhaps even upset that mitochondrial DNA gave such a clear picture when their own genetic methods, using hundreds of traditional nuclear gene markers (transmitted by both males and females), had for years indicated a more blurred division between Africa and the rest of the world. Several factors contributed to this blurring. Most important was the traditionalists’ classical, population-based approach to constructing mass-migration trees rather than building trees of gene lines. In effect, they persisted in following a broad, albeit mathematically based concept of ‘racial migration’ rather than tracing the migrations of individual gene lines found in those populations. Another important factor was the mixing and shuffling of nuclear gene lines at each generation – something that does not happen to mtDNA or NRY. Also, most of the gene markers they used had simple trees with a small number of very ancient branches, and the twigs were common to many populations.

For all these reasons, the traditional way of comparing populations of different regions by measuring multiple nuclear gene frequencies was a fundamentally flawed approach to looking at ancient migrations. As if to demonstrate this, a study by Oxford-based James Wainscoat and colleagues using nuclear genetic evidence from just a single nuclear locus (i.e. not Adam or Eve genes), and arguing for an out-of-Africa model, had already been published in
Nature
in 1986. This was a year before Rebecca Cann’s findings, popularized in the
Newsweek
article, and it used samples from human participants from all around the world, including samples I had collected in New Guinea in 1984. Instead of comparing frequencies of many genes, Wainscoat created a simple family tree of populations from just one genetic locus. The result was broadly the same as Cann’s findings in suggesting an out-of-Africa origin. Other geneticists also raised a series of highly technical objections to the analysis of the ‘Eve’ genes. The technical objections have since all been overcome one by one.
⁷

With the recent analysis of the other non-mixing system, the Y chromosome, and studies of many other genetic markers,
⁸
the original out-of-Africa picture suggested by the mitochondrial markers has emerged triumphant, and the multiregionalists have become an isolated, albeit vociferous minority.

Two routes out of Africa?

Humans had to come out of Africa in the end, as all their primate relatives had – but the timing and the route, as always, were determined by climate swings. There were two potential routes out of Africa, a northern and a southern, and the weather determined which was open at any particular time. The one that was open, in turn, directed the explorers where to go next – north, or east. Modern humans first left Africa over 120,000 years ago through an open northern gate. As we shall see, that first foray ended in disaster. Their second, successful venture set them on a path through Asia to
the south and east, already well worn by their predecessors. Europe was bypassed and ignored until 50,000 years ago.

Africa was the birthplace of all the various human species to walk this planet. This vast and isolated natural laboratory moulded humans over endless cycles of alternating desert and greening. The unique patchwork of savannah and forest that is sub-Saharan Africa is effectively separated from the rest of the world by two sets of environmental gates and corridors. For the last couple of million years these corridors have acted like a huge livestock corral, with several gateways alternately open and closed. When one set of gates was open the other was usually closed. One gate led north, over the Sahara to the Levant and Europe, while the other led east, across the mouth of the Red Sea to Yemen, Oman, and India. Which gate was open depended on the glacial cycle and determined whether mammals, including humans, migrating from Africa went north to Europe or east to Asia.
⁹

Today, Africa is physically linked to the Eurasian continent by only one of these corridors, via the Sinai Peninsula in the north. Normally an unforgiving dry desert, the potential route through the Sahara and the Sinai to the rest of the world opens, like some science-fiction stargate, only when variations in the Earth’s orbit and the tilt of its polar axis produce a brief episode of warming. This fleeting event in geological time happens only once every 100,000 years or so, when the Sun’s heat causes a polar meltdown and a warm and humid global climate ensues. The Sahara, Sinai, and the deserts of Australia grow lakes, become green, and flower in the short geological spring (
Figure 1.2
). But because this warm interlude is so brief, the North African weather-gate can act as a deadly trap to migrants.

For most of the last 2 million years, humans have shivered in the grip of the Pleistocene ice epoch, so the brief but marked warming of our planet’s surface, which opens up the gates of Eden, is known to geologists as an interglacial optimum. These short lush spells
contrast with the normally cold and dry glacial conditions of the Pleistocene. We modern humans have had only two such glimpses of paradise during our time on Earth. The most recent interglacial optimum was only about 8,000 years ago, and we are lucky to be still basking in the after-effects of its autumnal glow. For perhaps a couple of thousand years the Sahara was grassland, and all kinds of game from the south spread throughout North Africa and across into the Levant. Ironically, today’s pollution-driven global warming is actually helping to stave off the inevitable relapse into the cooler, drier, more unstable conditions that have characterized most of our time on Earth.

Usually, evidence for such climatic dramas in prehistory has to be teased out by scientists digging the ground and drilling into ice caps and the seabed. In this case, however, we do not need the abundant scientific record of archaeology and climatic change to demonstrate the truth to us. We can see for ourselves by looking at the wonderful paintings on cliffs in the central Sahara region. Thousands of naturalistic images of extinct buffaloes, of elephants, rhinos, hippos, giraffes (see
Plate 6
) ostriches, and large antelope, were painted there 8,000 years ago. This colourful historical record has continued intermittently up to recent times. Later paintings tell us that the Saharan game disappeared over 5,000 years ago, to be replaced by camels.

This period when African game briefly flowed into Morocco, Egypt, and the Levant was, on a larger scale, similar to rare downpours in deserts that activate the long-dormant seeds of beautiful flowers. The lush paradise was short-lived; the game retreated, and the desert returned. Big mammals do not have seeds that can hide themselves away in the sand. Even non-mammalian drought wizards like the desert frog and lungfish can only cocoon themselves for a short period while waiting for the next downpour. So also during the previous interglacial, the first in our time on Earth, a brave band of pioneers headed north out of Africa and reached the Levant before the Saharan gate slowly shut behind them.

Figure 1.2
   The Northern route out of Africa. This map shows vegetation in Africa during an interglacial such as happened 125,000 and 7–8,000 years ago. At these times grassland spread across the Sahara, allowing people from the south to follow the game into North Africa and beyond to the Levant. For simplicity, scrub and savannah are combined, as are semi-desert and extreme desert.

The earlier interglacial, known to scientists as the Eemian or Ipswichian, came 125,000 years ago, soon after the birth of our human family. We know that early modern humans travelled out of sub-Saharan Africa into North Africa and the Levant at a very early stage because their bones have been found in those places. In fact,
the earliest remains of modern humans anywhere outside Africa – dated to between 90,000 and 120,000 years ago – were found in the Levant.
¹⁰
The big question is whether they made a lasting impression there. It looks as though they failed to do so.

Out of Africa into Europe: the failed first exodus

Until these very early dates were confirmed, the out-of-Africa scientific camp assumed that the early northern exodus of modern humans to the Levant formed the nucleus from which Europeans and most Asians evolved. But there were basic flaws to these arguments. The early trail of modern humans sadly petered out in the Levant around 90,000 years ago. From climatic records we can see that there was a brief but devastating global freeze-up and desiccation 90,000 years ago that turned the whole of the Levant to extreme desert. After the freeze, the deserted Levant was soon reoccupied but this time by other, older residents – our first cousins, the Neanderthals – who were presumably forced southward to the Mediterranean by glaciers advancing from the north. We have no further physical evidence of modern humans in the Levant or in Europe for another 45,000 years, until the Cro-Magnon people made their appearance (as indicated by the presence of Aurignacian technology) 45,000–50,000 years ago and successfully challenged the Neanderthals for their northern birthright.
¹¹

Thus most authorities now accept that the first modern humans out of Africa must have died out in the Levant on the return of the dry glacial conditions that caused North Africa and the Levant to revert to extreme desert. Trapped in the northern corridor by the Sahara, there was no way back for them and few places to take refuge. The gap of 50,000 years between the disappearance of the first Levantines and the subsequent invasion of Europe obviously raises serious doubts about the prevailing theory that a northern African exodus gave rise to Europeans.
¹²
We shall now see why.

To help us to understand why many European archaeological and
anthropological authorities argue that Europeans arose separately from a northern African exodus, we need to acknowledge that there may be a Eurocentric cultural agendum in what a northern exodus tries to explain. Most important is the lingering twentieth-century European conviction that the Cro-Magnons who moved into Europe no more than 50,000 years ago (see
Plates 9
,
12
,
13
,
14
) defined the beginning of our species as ‘modern humans’ in the fullest intellectual sense. This human epiphany, with its extraordinary flowering of art, manufacturing skills, and culture, is known to archaeologists rather dryly as ‘the European Upper Palaeolithic’. For many of them, it was the creative explosion that heralded our coming of age as a sentient species. The magnificent cave paintings of Chauvet and Lascaux and the voluptuous, finely carved Venus figurines found throughout Europe date back to this culture.

The argument goes like this: if we ultimately came from Africa, and if this ancient artistic revolution that speaks so evocatively of abstract thought came from the Levant, then it is only a short walk from Egypt. Ergo, ‘we Westerners’ (for the proponents of this view are all European by origin) must have come from North Africa. The northern route is thus, for many experts, the conceptual starting point for out-of-Africa migrations. In the next chapter we shall see how it is logically impossible that Europeans were the
first
‘fully modern humans’, and how it was that Africans were fully modern, singing, dancing, painting humans long before they came out of their home continent.

There are real problems, however, in explaining how the sub-Saharan ancestors of Europeans could have got out through North Africa at that time. For a start, with an impassable Sahara Desert in the way for most of the past 100,000 years, any late North African invasion of Europe could only have come from a green refuge left in North Africa, such as the Nile Delta, after the interglacial from over 100,000 years ago. The Europeans could not have come directly,
non-stop from sub-Saharan Africa 45,000–50,000 years ago unless they floated all the way down the Nile on logs – which the genetic story denies.

A green refuge in Egypt?

If there was such a North African green refuge during the long dry period after the interglacial, it would thus have been the temporary home for European ancestors for at least 45,000 years. Green North African refuges there were, such as the Nile Delta and the Mediterranean coast of Morocco. The recent find of a child’s skeleton buried at Taramsa Hill in Egypt, dated to somewhere between 50,000 and 80,000 years ago, suggests that a relict population could just have survived there. Several leading out-of-Africa proponents are attracted by this possibility since it offers a clear explanation of the 45,000–50,000-year gap. Foremost among them is a champion of the out-of-Africa hypothesis, Chris Stringer, who is based at London’s Natural History Museum. He argues that the Egyptian child of Taramsa Hill belonged to a North African refuge colony and that the ancestors of Levantines and Europeans evolved out of such colonies from 50,000 years ago.
¹³