by Steve Jones
At the other end of Sahul, rising sea-levels soon marooned the inhabitants of Tasmania. They remained in ignorance of the world outside until the arrival of Europeans, in the eighteenth century. Nothing is known of the Tasmanians' genes, for a simple reason. They were driven to extinction (and sometimes hunted down) by ambassadors of the modern world's economy. There was a sordid episode in anthropology when the Tasmanians were regarded — absurdly — as the elusive 'missing link' between humans and apes and the museums of the world quarrelled over the bones of the last survivors.
Human traces show that even remote Pacific islands (such as Manus Island in the Admiralty group, three hundred and fifty kilometres from the nearest land mass) were occupied twenty-eight thousand years ago, so that by then it was possible to make substantial voyages. The genes of present day Melanesians, those from the islands north and east of Australia, still resemble those of the ancient populations in the Papuan highlands. They are the descendants of these ancient voyagers.
The Polynesians who occupy the rest of the Pacific are quite different and got there much more recently. Hawaii and Easter Island were reached only a couple of centuries after the birth of Christ. In the far Pacific, islands separated by thousands of miles of ocean are not at all distinct in their genes, proof that water is a less effective barrier to movement than is land.
Almost all the peoples of the distant Pacific carry a small change in their mitochondria! DNA. Nine letters of the message are missing. This deletion has spread through the whole of Polynesia from Fiji to New Zealand. In some places it is so common as to suggest that most of the present population descends from a single female who was the ancestor of almost all the inhabitants. It is shared with the populations of Taiwan and the Japanese, and shows that the Polynesians spread across the Pacific from Asia and not from Australia. Australian aboriginals and the Highlanders of Papua New Guinea do not have this genetic signature. They descend from a migration which began thousands of years before that of the Polynesian arrivistes.
One thing is clear: the inhabitants of the Pacific and those of South America have few genetic links. Thor Heyer-dahPs book of his intrepid voyage in a balsa raft across eight thousand miles of Pacific from Peru has sold twenty million copies, more than all other anthropology books put together. Unfortunately, his view that to reconstruct the past it is necessary only to relive it is wrong. Population genetics has sunk the Kon-Tiki.
Twenty thousand years ago, much of the Pacific had a dense population and a prosperous economy. In Europe, too, trade was well advanced. Flint for stone tools was transported for many miles and Baltic amber reached the Mediterranean. There was a brief rise of art, perhaps a mere couple of centuries long, which tilled the caves at Lascaux and Altamira with images.
While the world economy boomed the Americas were empty. They were at last reached from Siberia. Many of the inhabitants of that icy land, which was even colder than it is today, lived by hunting mammoths. As they spread they destroyed their food sources. At last, they came to the Bering Land Bridge which joined Asia to Alaska. It emerged from the sea, as did thousands of square miles of coastal plains all over the world, as water was locked into the ice. At the end of the ice age the water rose and twelve thousand years ago the bridge between Old and New Worlds was breached. Just before it disappeared, a few pioneers made their way across. If their experiences were like those of what we know of the nineteenth-century Inuit who made long voyages across such barren landscapes they had a grim time. Many must have starved. Nevertheless, some reached the broad plains of North America and soon spread to the continent's southern point, reaching it within a couple of thousand years. This seems like a rapid expansion but is, after all, less than ten miles a year into a deserted land. The journey was helped by a brief warming which meant that, even in Alaska, a few trees appeared in the bitter landscape.
Once again, the edible inhabitants suffered. Mammoths, sloths, giant tapirs and camels followed each other into extinction. Each was large, tasty, naive and tame. They reproduced slowly. Once humans had arrived their fate was certain. The wave of destruction tempted the first Americans south until, in Patagonia, they could go no further.
The date of the American invasion is not certain. The oldest traces of occupation in North America are in a rock shelter in Pennsylvania. They date from about twelve thousand years ago. Soon, members of the 'Clovis culture', in what is now the United States, could produce sharp and effective arrowheads. The first art in the Americas is at the cave of Pedra Furada — the Perforated Rock — in Brazil, which has twelve-thousand year-old imam-s of birds, deer and armadillos, together with human stick figures. Some claim that charcoal from nearby caves dates back for fifty thousand years, but few anthropologists accept (his as evidence of human occupation. Most believe thai ilu* first Americans arrived less than twenty-five thousand years before the present.
The genes of Native Americans fit the idea of a small band that filled a new-found land. Americans as a whole are less diverse and more uniform than arc the peoples of highland Papua New Guinea (who fill a tiny proportion of the space). The mitochondria! genes of all Native Americans fall into four major lineages as a hint that just a small group managed to complete rhe hazardous traverse of the Bering Bridge. The same ones are found in some three-thousand year-old Chilean mummies, implying that there were not many bottlenecks on the way through the Americas from north to south. The mitochondria of South American Indians resemble those of north-east Asia, supporting the idea that their ancestors, like those of Polynesians, came from that part of the world (although there is a hint of an ancient link with Europe in a few Northern tribes, suggesting that a more distant traveller across the land-bridge helped found some American groups).
By ten thousand years before the present, humans had filled the whole habitable world, apart from some remote islands. Everywhere they lived in small bands. Every Englishman needed ten square miles of land to feed himself.
The global spread was accompanied by technical advances in axes, arrowheads and nets as the animals easiest to exploit — reindeer, mammoths, giant kangaroos or emus — disappeared and the hunters were forced to move to less easy prey.
The genes of the few modern peoples who still live as hunters and gatherers are a window into that way of life. Adjacent groups often differ quite markedly from each other, evidence that their social structure led to genetic isolation. There were more opportunities for random change as each band split and moved on as the globe was filled. No doubt the days of a hunter-gatherer were rather lonely. Although the immediate group may have been close-knit, there was little contact with anyone else.
Eight thousand years ago, everything changed. There was an economic breakthrough that was to shape the society and the genes of the modern world. Farming began.
Before agriculture, people ate dozens of kinds of food. An excavation in Syria uncovered more than a hundred and fifty kinds of edible plant, but after the onset of farming the diet shrank, to a few cereals and pulses. Even in the nineteenth century, Queensland aborigines ate two hundred and forty different species of plant. To add together the top five crops in the world today gives a global total of just a hundred and thirty kinds.
Hunters had an easier time than did the first farmers. The few!K.ung Bushmen who until recently lived in this way needed to work for just fifteen hours a week to feed their families, far less than those who moved to the farming economy (and less than the time which most Europeans have to spend at work to pay the weekly food bill). In the Middle East, too, wild grasses are abundant enough to allow a family armed with primitive sickles to gather enough seeds in a few weeks to feed themselves for a year. Perhaps the extra effort explains the Bible's disparaging tone about the new economic system: Adam, on the expulsion from his hunter-gathering Eden was admonished: 'Cursed is the ground because of you; in toil you shall eat of it all your life. therefore the Lord God sent him forth from the Garden of Eden to til! the ground from which he was taken.'
T
he earliest farmers lived in the Middle Hast, most of them around the headwaters of the Tigris And Euphrates, in a tight core of fertile land in what is now south-Eastern Turkey and northern Syria. Later, farming appeared in the basin of the River Jordan (which is close to where the Biblical Eden must have been). There was plenty of natural food around in what was then a fairly verdant landscape. It was difficult to move elsewhere when times got bad, because of the deserts all around. Rather less than ten millennia ago the weather began to change. There had been a continental climate rather like that of the Midwest of the United States today. Winters were cold and wet and the summer was hot with plenty of rain. Suddenly it shifted towards a Mediterranean climate with warm wet winters and hot dry summers. The lake of Jordan itself began to dry up, and its fresh waters split into the salty Sea of Galilee and the Dead Sea.
Pollen shows that the plants began to change too. The forests shrank and grasses took over. Mediterranean climates are good at fostering the evolution of new plants. Soon there were new and fertile hybrids between grass species that came together as the countryside dried. The local people burnt the grass to attract deer and gazelles to its new shoots. In a few years, they began to plant the seeds, and farming began. Einkorn wheat — one of the ancestors of today's crops — was domesticated close to the Tigris, the relative with which it hybridised in a great crescent from today's Iraq to Israel. Barley, lentils, peas and bitter vetch all found their home within a few scores of miles nearby. Farming itself may have been a very local pastime for a thousand years and more, before the crops and their guardians began to fill the Fertile Crescent about seven thousand years before the present. The teeth of those ancient agriculturalists are worn, because the first grains were milled on soft grindstones and their food was full of grit.
The same sort of thing happened at about the same time in other places. After a transition period in which grass was burned to harvest the new shoots or wild strands of vegetation were watered, agriculture spread at a great rate. Wheat was first cultivated in the Middle East, rice in China and maize in South America. Somewhat later came the domestication of sorghum, millet and yams in West Africa. The effect was always the same: a population explosion. Before farming, each person needed about a square mile to feed himself. After it, a hundred people could live off the same space.
Fossil bones suggest that the health of farmers, far from improving, got worse. Deficiency diseases appeared as the amount of protein went down and there were periods of starvation as population outgrew resources. If children eat well, they grow up tall. This is why the average height in most Western countries has gone up by three inches in the past century. For the children of the first farmers — like those of the proletariat of the Industrial Revolution — the opposite happened. In south-east Europe the average height of men fell by seven inches in the millennium when farming began. The bones of North Americans show extensive damage, most of all in the eye sockets, as maize became the main foodstuff. Maize has little iron and, even worse, reduces the absorption of that essential mineral from other sources such as meat. This led to an outbreak of anaemia, whose record is preserved in the skulls of those who depended on the new maize economy.
Population growth meant that the new habits soon spread. Waves of technical change radiated from each centre of origin. In Europe, decorated beakers appear in archaeological digs, and in the Far East implements of rice cultivation spread for thousands of miles from their Chinese homeland.
From its origin in the Middle East about ten thousand years ago, agriculture reached Greece about five thousand BC and took more than two millennia to cross Europe. Its expansion was not regular. The frontier was rather like that of the nineteenth-century Wild West. The colonists settled the best areas first and left the less valuable lands to their original inhabitants. In north and east Europe, hunter-gatherers managed to stall the wave of farmers from the Danube basin for a thousand years. Their northward spread was further slowed by a worsening climate which made it hard to grow crops. The new technology did not reach Britain until about five thousand years ago. Elsewhere, it was delayed for even longer and in southern Finland the novel economy did not begin until after the time of Christ.
Much of the resistance to the farming way of life was due to the success of the hunters of the 'Forest Neolithic'. Nine thousand years ago northern Europe had a population of affluent foragers. They lived in large camps, built traps for their prey, and stored great caches of food. Around the Baltic, they built stilt villages in ice-dammed lakes. In some places, hunters specialised on seals and in others on deer. Those who gathered ate thirty or more different plants — grasses, acorns, sorrel and dandelions and, in marshy places, water-chestnuts. Millions of broken water-chestnut shells have been found, together with the wooden mallets used to smash them. The single crop was flax, used for rope rather than food.
Wherever farming arrived, the local hunter-gatherers suffered, sooner or later, a process of gentrification as a wave of economically advanced people moved in on them. It is easy to imagine the complaints of the natives as the newcomers with their new-fangled ways and high technology disrupted their rural idyll. Life in southern England five thousand years ago had quite a lot in common with that depicted in the BBC radio series The Archers today.
The farmers may have overwhelmed the hunters but there was a long period of coexistence. Farmers traded grain for meat and furs. In some places, the transition from the old to the new economy took a thousand years, with a slow decline in the number of bones of wild pigs and deer and of natural grasses (as shown by the impressions of their seeds in fragments of pottery) in favour of cattle and grains. The decline in climate at last put paid to hunting. Oysters and seals disappeared from the Baltic and the northern hunters at last moved into the modem world.
Economic historians have two views of the origin of technology. One theory has it that knowledge itself moves, rather than the people who know: new methods are passed from group to group. The other claims that cultural advance comes from displacement and the conquest of one people by another. The sophisticated bring their knowledge with them and replace their predecessors. Bones, pots and seeds hint at the nature of the European Community ten thousand years ago; but the genes say more. Genetic patterns in today's Europeans show that both migration and diffusion were involved in the replacement of hunting with agriculture. The farmers did move in on the hunters, but, just as in The Archers, social barriers did not stop sex across the dass divide.
To reconstruct the history of Europe from genes is difficult, because it is one of the more tedious parts of the world, with rather little change from place to place. A genetic map based on dozens of genes from hundreds of places does hint at a general trend from south-east to north-west, from Greece to Ireland. This map looks rather like that of the wave of advance of farming, based on the spread of agricultural implements. Farmers moved on at about a kilometre per year by founding new farms at the edge of their expanding population. They interbred with the local hunters and, because they were much more numerous, absorbed their genes. This process began in the Balkans and was completed thousands of years later on the western fringes of Europe. By the time the farmers reached the far north and west their genes had been much diluted with those of the aboriginal Europeans. As a result, the British contain more hunting DNA than do, say, the Greeks, who descend from a less adulterated wave of immigrants who had rolled over the earlier economy and absorbed its genes. The biological heritage of hunters and farmers means that today's Britons are more related to the Portuguese than to the Serbs. The latter live about the same distance away but are closer to the Middle Eastern source of agriculture.
The history of European women — as defined by mitochondria! genes — is not quite so clear. They are divided into half a dozen or so major clusters and a few minor groups^ most of whom split apart at some time during the end of the Stone Age, perhaps as the ice retreated across the continent. Although the frequency of each varies from place to place, the geog
raphy of mitochondria is harder to fir into a historical narrative than is that of genes that pass through both sexes. There is a hint of an east-west trend along the Mediterranean coast, which might reflect the movement of farmers' wives, but no sign of this further north.
The genetic map of Europe has a few anomalies. The Basques do not fit into the general pattern. They have a number of unique features, with the highest frequency of the Rhesus negative blood group gene in the world. Excavations show that the locals resisted the new technology for thousands of years. They still differ from all other Europeans and may be closer to our hunting ancestors than anyone else (although their mitochondria are not distinct from those of their neighbours). The Lapps, too, are distinct and descend from a different group of hunters, whose society they still in part retain. Sardinians are also rather different from the rest of Europe and have affinities with the Basques. The remoteness of their island home may have reduced the number of immigrants.
There are also genetic trends away from a Middle-Eastern centre to the north-east towards Siberia, the southeast in the direction of India, and, more ambiguously, south-west into North Africa. Perhaps these too reflect of a wave of farmers on the move away from a population explosion who absorbed the genes of the local inhabitants as they spread. One North African group, the Berbers, now scattered in tribes across Morocco, Algeria, Tunisia, Libya, and Egypt is shown by its mitochondria to be distinct from the Arabic-speaking peoples who surround them. They fit instead into the European family of female lineages and may be the remnants of another branch of the first wave of farmers, who passed south of the Mediterranean.