Out of Eden: The Peopling of the World (49 page)

How early was the coastal route free of ice and open? From 14,000 years ago, it seems. Daryl Fedje of Parks Canada. British Columbia, and Heiner Josenhans of the Geological Survey of Canada have used high-resolution sonar to make a detailed map of the ocean floor off the north-west coast of Canada.
⁸¹
The area they chose is around the Queen Charlotte Islands, just south of Alaska. Their map shows a new world of former rivers meandering down around flood plains and ancient lakes. The plains would all have been above sea level and free of ice from after 14,000 years ago for a few thousand years – that is, until the continuing sea-level rise drowned the land again. Armed with this new map of the drowned coastline, the researchers went out to collect wood from the flooded forests. They pulled up the stump of a pine tree and other bits of wood from the ocean floor, which they carbon-dated to 12,200 years ago; they even found remains of edible shellfish of the same age. From a slightly younger beach of 10,000 years at 60 metres (200 feet) below sea level they found a stone tool, the earliest tool on the north-west coast of America.

Putting this all together, it does seem that from 14,000 years ago there was a way for humans to move from Beringia and Alaska and down the west coast of America, completely bypassing the ice caps. There is also evidence that they were there at least 10,000 years ago. Furthermore, the evidence from the west coast of South America shows that the same beachcombers, with the aid of coastal vessels, could have made it all the way down from Beringia by 11,000 years ago.

The west-coast route gives one geographical explanation for the late spread of Group B as advocated by Yelena Stariovskaya. B4, the American founder line, was also spreading into the islands of eastern
Indonesia, presumably by boat and far to the south in the south-west Pacific, around 17,000 years ago (see
Chapter 6
). The coastal bypass route also has the unexpected potential of making the ice barrier and ice corridor dates irrelevant to the Clovis story. When I visited Knut Fladmark at Simon Frazer University, Vancouver, I was surprised to find he was a convinced Clovis-first conservative; but the Clovis-first position is to some extent shored up by the bypass.

Pre-Clovis only

Can we put this back into the larger genetic picture of the peopling of the Americas? I think we can. In spite of the sparse evidence, I find the story of the alternative west-coast trail compelling as a parallel route of colonization, but not the only one. For Group B4 to have been on the west coast of Canada 12,000–15,000 years ago, it seems to me more likely that – as with the ancestors of the west-coast brown bears – their ancestors were already resident in Beringia with the other lines (A, C, D, and X) before the LGM. The alternative, that B4 raced out of Asia along the coast only just after the LGM, would not have been feasible: there were major coastal barriers, such as the Aleutian ice sheet, to negotiate between the East Asian coast and British Columbia during the LGM and its immediate aftermath.

So, I still go for the entry of all the ancestors of the Native Americans to Beringia and the Americas before the LGM and before Clovis. The genetic picture for A, B, C, D, and X founders suggests multiple parallel entries into the Americas before the LGM via different routes, by pioneer groups coming ultimately from the north-eastern Eurasian steppe and the east coast of Asia. They may have looked variously like Europeans and like the Ainu and some Pacific islanders. Also at this stage, some, like the ancestors of Wizards Beach Man, looked more like Northern Mongoloids and recent Native Americans. They spread throughout the Americas, perhaps more rapidly via coastal beachcombing. The B4 line (or one
particular B4 line) may have entered at this early point and made it down to South America, where, in contrast to her relative youth in North America, she is now as old as the other founders. Then came the ice age. Those left in Beringia north of the ice caps went through the most dreadful privations, but descendants of Group A survived the deep freeze to emerge as skilled fishermen, the ancestors of the Na-Dene and Inuit-Aleut speakers. The B4 group may have sat out the ice age on the west coast and then re-expanded inland, like the brown bears, or there might possibly have been a fresh introduction of Group B from Asia running up, round, and down the Pacific Rim coastline. As far as we know, however, America and Alaska (the remnant of the lost continent of Beringia) had no further significant Asian genetic input from the time of the LGM until the time of Leif Eriksson and the human tidal wave that followed Columbus and his ‘discovery’ of the New World.

E
PILOGUE

S
EVEN MILLION YEARS AGO
, cool dry weather devastated the habitat of forest-dwelling ape species. Some time thereafter, the first evolutionary steps were taken towards the two-legged, large-brained creature we call
Homo sapiens
. Palaeontologists have yet to agree on exactly when anatomical evidence for bipedalism appears in the fossil record, and whether the split with the ancestors of chimps occurred 5 or 7 million years ago, but those steps clearly were taken. While the first walking ape to evolve,
Australopithecus
, had the same moderately large brain as chimps, this too changed as further genera evolved. With the intensification of the dry cool phase a little over 2 million years ago began a dramatic growth of the brain, which happened only in humans who appeared around that time and their sister-genus
Paranthropus
. The rapidity of that initial change was never to be repeated.

Biology and culture: coevolution

Something new these two new genera of hominids were doing gave them both a special advantage in this period of increasing aridity. The new behavioural resource did not seem to be linked to a specific diet since subsistence differed widely between the two genera, but it
selected for, thus presumably benefiting from, a larger brain. During this phase of human evolution our brains grew rapidly while our bodies changed little. The rate of proportionate increase in brain size was at its maximum near the birth of the
Homo
genus, supporting the implication from
Paranthropus
that our pre-human ancestors already possessed that unique new behaviour which subsequently drove human evolution. The most obvious candidate ‘unique behaviour’ which would benefit from a large brain is the same one which still separates us from all other living species, namely
speech
. But, in the absence of prehistoric cassette recorders, the most obvious physical evidence of cultural change was that, from the start, humans fashioned stone tools.

In spite of the rapid brain enlargement, progress in tool-making was painfully slow for a million years and new technology did not automatically follow the appearance of each new human species. Acheulian-type stone tools were invented by African
Homo erectus
1.4 million years ago, but this was long after the ancestor of Asian
erectus
had left the home continent. Acheulian technology therefore did not enter Eurasia until the next exodus.

Humans as mammals

The human story over the last 2.5 million years has been punctuated by great leaps in technology and world exploration separated by long periods of fallow. A common perception is that our ancestors were climbing an evolutionary stairway of achievement and ability, on which each new step had been unavailable to their immediate ancestors. From this Utopian standpoint we are merely the latest in a long line of ever-improving models. This view carries with it the implication that, all along, we have been the masters of our destiny, our limits of colonization set only by the intelligence and resourcefulness of whichever of our species was dominating the planet at any given time. Such an optimistic view of our intelligent self-determination is overstated.

One of the first humans,
Homo erectus
, made it rapidly out of Africa to colonize the whole of Eurasia. They were not, however, the first ape to do so, as can be seen from the orang-utans and gibbons that inhabit Southeast Asia. Nor were they the last humans to make the exodus before ourselves. Compared with earlier humans, our recent ancestors’ only
additional
globetrotting exploits were to have reached the Americas and the Antipodes. Our recurrent expansions were also mirrored by other mammalian genera, and were determined mainly by climate and geography, following the two well-worn paths out of Africa. We differ from other large mammals, but not much from rodents, in the great variety of habitats we now occupy and in the population densities we have achieved. In this context, we differ from rodents only in that, being large, we consume vastly more resources per individual.

Human movements out of Africa via the northern and southern routes were always determined by the climate cycle and the availability of resources. The grinding glacial cycle not only opened and closed the gates out of Africa but also periodically squeezed local populations through the mangle of near-extinction to produce new, larger-brained humans to stay at home or leave their African birthplace to try their luck elesewhere.

Our brains stopped growing long ago

In Africa by 1.2 million years ago the brains of
Homo rhodesiense
had grown to within 6 per cent of the volume of modern humans. Around 300,000 years ago, the climate-driven brain-growth machine reached a plateau of size 11 per cent above that of today’s people. Since then our brains and bodies have got smaller. The glacial cycles of boom, stress, and bust continued unabated; but except for cosmetic changes in limb proportions, eyebrows, and skull shape, the gross physical evolution of the human genus had by now slowed to a snail’s pace. Perhaps, as with cars, there was a law
of diminishing evolutionary return, and it was no longer economical to build models with ever larger engines.

As anthropologists Sally McBrearty and Alison Brookes argue persuasively, the real physical and behavioural threshold of
Homo sapiens
was reached at that point. Under this view, Anatomically Modern Humans are merely a later race which developed out of the older, so-called archaic
Homo sapiens
after another glacial near-extinction in Africa 150,000 years ago. There is evidence that archaic
Homo sapiens
types themselves also left Africa to colonize Eurasia long before we did.

Cultural evolution took over

In the picture McBrearty and Brookes draw, all the discriminating elements of behavioural modernity can be traced back to the African Middle Stone Age. That is not to say there was a technological big bang 300,000 years ago. Their evidence emphasizes the subsequent acceleration in human technology, first slow, then faster and faster. The early advances were individually rather minor and late to appear, but as more and more knowledge began to be transmitted and accumulated down the generations as compound interest, cultural evolution began to leave genetic evolution far behind. Looked at another way, if cultural evolution really took over from genetic evolution 300,000 years ago, then the differences between us and them are merely cultural and archaic
Homo sapiens
individuals could well have the intellectual potential to put a man on the Moon if they were living among us today.

The story of the genes: how it helps

What can the new genetic tools tell us about ourselves and our ancestors that such perceptive palaeoanthropologists and archaeologists have not already sketched out? The answer is much, as
I hope this book has shown. Genetic palaeontology brings clarity to a field of near-medieval confusion. The measurement of skulls and their shapes and the documentation of stone tools and their dates alone lead to an imperfect view of human prehistory. Apart from the paucity of Palaeolithic skeletal remains, there is enormous variation in human skull shape. The use of skull shape as a marker system to determine ethnic relationships has been further confused by the effects of under-nutrition and stunting in traditional agricultural societies and also by unknown proportions of admixture between different groups of humans. This all makes it quite easy to poke holes in reconstructions of the prehistory of human migrations based on such measurements. While stone tools are far more abundant than human bones, they are also a one-sided view and can only tell us about the received culture of their makers, not necessarily about their origins, migration routes, or biology.

The two best examples of controversies that rumble on among anthropologists as a result of these imperfect tools are, first, the multiregional versus out-of-Africa theories of modern human origins, and second, whether or not there was interbreeding between Neanderthals and the first modern Europeans – the Cro-Magnons. Classical population genetics using simple protein markers gave as blurred a picture as did studies of skull shape. The unadulterated direct transmission of the Adam and Eve genes down the generations has changed all that.

Clear genetic trees for both modern Y chromosomes and mtDNA point back to a recent common ancestor of all modern humans within the last 200,000 years and a migration out of Africa less than 100,000 years ago. This new line rather quickly replaced all preexisting human genetic lines, including the Neanderthals. Admittedly there could have been interbreeding between archaic and modern
Homo sapiens
, but there is no convincing evidence for this in our male and female gene lines. So, if there was miscegenation it
would have been rather small-scale, and the ancient lines would have become extinct. Some have suggested that traces of such past interbreeding could reside undetected in our vast nuclear genome, but the key word is ‘undetected’. Because of their tendency to recombine and mix at each generation, it is difficult to draw unambiguous trees of nuclear genes, so there will always be questions.