Steve Jones - The Language of the Genes

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.'

The 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.