by Steve Jones
The migrants also brought, quite unawares, some rare genes drawn by chance from the people of Holland. One of the partners in the marriage of Gerrit Jansz and his wife Ariaantje Jacobs (who was one of a group of girls sent from a Rotterdam orphanage in the 1660s) must have carried a copy of the gene for a form of porphyria. This disease (which is related to that which may have afflicted George III) is due to a failure in the synthesis of the red pigment of the blood. Sometimes, light-sensitive chemicals are laid down in the skin. **** they react with sunlight and produce painful sores. In certain forms of porphyria hair grows on exposed areas. Sometimes the waste material accumulates in the brain and leads to mental disorder. Part is excreted in the urine, to give a characteristic port-wine, almost blood-red, colour. Werewolves — creatures that come out at night, howl and drink blood — may have begun with the porphyria gene.
The South African form is mild but became important when barbiturate drugs were used in the 1950s. Carriers of the gene suffered pain and delirium when they took them. Porphyria is rare in Europe, but thirty thousand Afrikaners bear it. Johannesburg has more carriers lhan does the whole of Holland. All descend from one member of the small population of founders that grew in numbers to produce today's Afrikaners. Because it is so common in one family, porphyria in South Africa is sometimes called 'van Roojen disease'. A gene and a surname tell the same story.
The founder effect can be seen again and again among the descendants of those who colonised the world from Europe. Sometimes, the settlements are isolated by miles of ocean. Tristan da Cunha, a tiny island in the South Atlantic, was settled by a garrison sent to guard Napoleon, then in exile on St Helena. A few soldiers stayed on after the guard was withdrawn. They obtained wives by advertising, and a few shipwrecked sailors and others joined the community over the years. It went through a second bottleneck when several men drowned in a fishing accident and some families moved away, with the advice of a gloomy pastor. Now, the island is still a week's journey by ship from the mainland, but a few hundred people can stand the isolation. Again, they share names, seven altogether, and those — Bentley, Glass and Swain — of three of the first founders, are still common. Just five lineages of mitochondria! genes exist, and the island has its own genetic abnormality, a hereditary blindness brought by one of tlu- original wives.
Some migrant communities are isolated by social rather ih.in physical barriers. The United States has many religious groups whose founders emigrated to avoid persecution. They have grown into large populations which exclude outsiders. The Pennsylvania Amish have a unique inheritance. Almost a hundred babies have been born with six fingers and restricted growth, a condition almost unknown elsewhere. Every one of the affected children descends from Samuel King, a founder of the community.
To trace the movement of a gene around the world also shows the importance of chance. Huntington's Disease is relatively common among Afrikaners. Most cases descend from a Dutch man or his wife who emigrated in the 1650s. All copies on Mauritius are the legacy of a French nobleman's grandson, Pierre Dagnet d'Assigne de Bourbon, and more than four hundred patients in Australia have inherited their gene from a British immigrant, Mrs Cund-ick. Wales has a patch of the disease in the Sirhowy Valley, around the house of a mason who settled there in the nineteenth century and who must have carried the Huntington's gene. The largest kindred in the world (which was used to map the gene) is in Venezuela around an arm of the sea called Lake Maracaibo. Ten thousand descendants of one Maria Concepcion, who died in about 1800, have been traced. Four thousand either have the illness or are at a high risk.
Such accidents of colonisation must have happened again and again as humans spread across the world. Even without a written history, the surnames of the Afrikaners make it possible to estimate how many people were in at the beginning, three hundred and more years ago. Genes can do the same job. Patterns of variation show how many people founded a population, or whether it went through a bottleneck in the distant past.
Inherited diversity shows clear global patterns. Africans are more variable than are the rest of the world's peoples. Their cell-surface antigens (the cues recognised by the immune system) show about twice as much variation as do the equivalent genes in Europe, and many nf its variants are unique to Africa. Africans are more van.ibli- for blood groups, proteins and DNA sequences as well. 1'or mito-chondrial DNA, the average difference between two Africans is twice that found elsewhere. Venezuelan Indians, in contrast, whose ancestors were near the end of the long history of movement across the world from Africa, have almost no variation in their mitochondria! DNA.
The decrease in diversity outside Africa, humankind's native continent, may be because genes were lost as small bands of people moved, split and founded new colonies in the trek across the globe. Just as for Afrikaner surnames the number of variants dropped each time a new colony was founded. The high levels of diversity among Africans is evidence that Homo sapiens has been in that continent for longer than anywhere else. Its decrease at the tips of the evolutionary branches in South America and Polynesia shows how human evolution was driven by chance as the migrants passed through a succession of bottlenecks.
A comparison of the genes of Africans with those of their descendants elsewhere in the world makes it possible to guess at the numbers involved in those early colonisations. The order of bases along a short length of DNA is in some ways a 'genetic surname', a set of inherited letters which pass together as a group down the generations. The name written in nucleic acids around one of the haemoglobin genes has been looked at in detail worldwide. The results are quite unexpected.
All populations outside Africa, from Britain to Tahiti, share a few common sequences. Africa itself has a different pattern of distribution. Just like the names in the Johannesburg telephone book compared to that of Amsterdam, the shift in pattern from the ancestral continent to its descendants may be a relic of a population bottleneck at the time of migration — this time from, rather than to, Africa. We can do some statistics (and make quite a lot of guesses) to work out the size of this hundred-thousand-year-old group of emigrants. They show that the whole of the world's population outside Africa may descend from fewer than a hundred people. If this is true, non-Africans were once an endangered species.
Science has two cultures: one (to which most scientists belong) uses mathematics and the other understands it. Such guesses about ancient population bottlenecks demand statistical acrobatics. They also depend on one crucial, and perhaps quite mistaken, assumption; that the genes involved do not alter the chances or survival or of sex. Molecular biologists tend to assume that small changes in the structure of DNA are unimportant. It is just as possible that they do have an effect on fitness. If, for example, Africans have more variation on the surfaces of their cells because it helps to combat disease, then to claim that a reduction elsewhere is due to an ancient bottleneck is simply wrong.
Any attempt to reconstruct the distant past is bound to suffer from ambiguities such as these. Genetics has not yet revealed just how many Adams and Eves there may have been, but shows that much of the human condition has been shaped by accident: an observation that might at least instil a certain humility into those whose genes have defeated the i iws of chance by surviving to the present day.
Chapter Ten THE ECONOMICS OF EDEN
Renaissance painters on religious themes hat! a problem: when they showed Adam and Eve, should they have- navels? If they did, then surely it was blasphemous as it implied that they must have had a mother. If they did not, then it looked silly. Although some compromised with a strategic piece of shrubbery, that did not resolve matters. And where was the Garden of Eden? Various theories had it in Israel, Africa and even the United States. When it existed seemed obvious because to add up the ages of the descendants of the primal couple as given in the Bible set the start of history as 4 October 4004 BC.
The reason for leaving Eden was also clear. Its inhabitants had, with the help of an apple, learned forbidden truths,
and as a punishment were forced out into the world. No longer could they depend on a god-given supply of food falling into their hands. Instead, they had to make a living. The first economy was born.
The escape from Eden — the colonisation of the Earth — showed how genetic change is linked to economic development. Economics is often seen as a kind of enlightened self-interest. The desire to increase one's own wealth may, as Adam Smith has it, be the invisible hand which is at the foundation of all social progress. The same argument is used by some evolutionists. Genes are seen as anxious to promote their own interests, even at the expense of their carriers. In its most naive form, this view of life is used to explain (or at least to excuse) spite, sexism, nationalism, racism and the economic and political systems that grow from them.
Theories of economics and of evolution have obvious ties. Darwin was much influenced by the works of Malthus, who had been disturbed by the new slums of the English cities of the eighteenth century. In his Essay on the Principles of Population Malthus argued that populations will always outgrow resources. That notion led Darwin to the idea of natural selection.
Karl Marx, himself a denizen of one of the most congested of London districts, was just as impressed by the dismal conditions of the new proletariat. He sent Darwin a copy of Das Kapital (which was found unread after his death). Marx, in a letter to Engels three years after The Origin of Species, went so far as to say that 'It is remarkable how Darwin recognises among beasts and plants his English society, with its division of labour, competition, opening up of new markets, inventions, and the Malthusian struggle for existence.1 Engels took it further. In his essay The Part Played by Labour in the Transitioft from Ape to Man he argued that an economic change, the use of hands to make things, was crucial to the origin of humans. If one substitutes the term 'tools' for 'labour' his views sound rather like those of modern students of fossils.
Genetics shows that much of evolution is, as Engels said, linked to social advance. However, far from society being impelled by its genes, social and economic changes have produced many of the genetic patterns in the world today. Every technical development, from stone tools on, has led to an evolutionary shift and to biological consequences that persist for thousands of years. Society — and most of all the economic pressures that cause people to move — drives genes, rather than genes driving society. Relentless expansion is at the centre of human evolution: in Pascal's pessimistic words, 'AH human troubles arise from an unwillingness to stay where we were born.'
Fossils show that almost as soon as they evolved, humans began to migrate. Why our ancestors were so restless, nobody knows. Technological progress may have been involved, as the emergence of modern humans coincided with improvements in stone axes and the* like (although tools had been made for at least two million years before the great diaspora).
Perhaps climatic change was as important. The Sahara Desert was once a grassy plain and Lake Chad a sea bigger than the present Caspian. Both dried up about a hundred thousand years ago, so that food shortage may have driven man out of Africa. A microcosm of that process is taking place at the southern edge of the Sahara. As the rains fail, the desert has spread into the Sahel and migrants are on the move.
The earliest economies had a simple foundation. People used what nature provided, until it ran out. The world is filled with fossils of large and tasty animals that were driven to extinction soon after humans arrived. In Siberia, so many mammoths were killed that the hunters made villages from their bones. In Australia, too, there was a shift from forests to grasslands as the immigrants burned their way across the continent. The record of destruction is preserved in the Greenland ice-sheet. The snows which fell tens of thousands of years ago retain the soot and ash from gigantic forest fires set by our ancestors.
New Zealand was not colonised until the time of William the Conqueror. For a few years there flourished a culture based on the exploitation of a dozen species of moas, giant flightless birds. The ritual slaughtering grounds where the birds were killed (and where half a million skeletons have been found) are still around. The birds themselves are not. In Europe, too, whole faunas went not long ago. Humans did not reach Crete, Cyprus and Corsica until around ten thousand years before the present. Before then they had some extraordinary inhabitants; pygmy hippos, deer and elephants, and giant dormice, owls and tortoises. Soon after the arrival of the first tourists, all were gone, and the burnt bones of barbecued hippos are scattered among the remnants of the earliest Cypriots.
The common large mammal in Europe and the Near East at the time when modern humans moved from Africa was one of their own relatives, Neanderthal Man. He had lived there quite happily for two hundred thousand years. Many Neanderthals found homes in the dense forests of southern France. Some had an economy based on hunting reindeer, with settlements concentrated around their migration routes. The cave of Combe Grenal in Perigord contains tens of thousands of Neanderthal stone tools. Their culture was, in its own way, sophisticated; but it did not progress and showed no real change for a hundred thousand years. Tools in Britain and the Middle Hast look almost the same. Those who made them had little interest in exploration and never made boats, so that the delights of the Mediterranean islands (hippo-infested though they were) remained unknown. Neanderthals were the first conservatives.
Soon after the invasion of Europe by our own direct ancestors, they disappeared. Why, we can but guess. The guesses range from genocide to interbreeding. The first is unlikely. In France, at the cave of St Cesaire, Neanderthals and moderns lived close to each other for thousands of years. The second is probably wrong. If there had been sex between the indigenous population and the invaders, then modern Europeans would be expected to retain genes from this distinct branch of the human lineage and to have genes distinct from those of today's Chinese or Indians, whose ancestors never met a Neanderthal, let alone mated with one. They do not. Perhaps economic pressure did away with those ancient conformists. For most or history, Africa was the most advanced continent. Africans made sharp blades while Europeans had to manage with blunt axes. There was a period when Neanderthals seemed to pick up some of the new technology, but it did not last. The Hist modern Europeans were found in 1868 during railway work, in the Cro-Magnon shelter at the Perigord village of I.es Kyzics. Cro-Magnons looked much like modern Europeans. They (and their immediate predecessors the Aurigiuicians) had a sophisticated hunter-gatherer economy and made a variety of tools. Their cave art reached its peak around forty thousand years ago. The moderns had tools made of bone and ivory when their relatives sriil were satisfied with stone. They were better at exploiting what was available, so that their populations grew faster. That drove Neanderthals (and their genes) out. The last known skeletons are from St Cesaire. They died more than thirty thousand years ago.
Simple as it was, the Neanderthal economy held our ancestors at bay for a long time. The moderns reached Australia before they filled Europe. Competition from its indigenous inhabitants may have kept them out.
Most of the globe was populated at some speed after humans left their natal continent. The first Australians arrived about sixry thousand years before the present. The earliest remains are in two sites in Arnhem Land, in north Australia, which contain stone tools and ochre paints in a sandy deposit. The sites are close to the shore and perhaps to the point where humans arrived from rhe north. Soon, its inhabitants had complex tools and fishing nets and were economically as well developed as the rest of the world.
For much of its history Australia was joined to what is now New Guinea by a land bridge. It disappeared just seven thousand years ago. Tasmania was also part of Greater Australia. That great continent, Sahul, has always been separated from Asia by a deep trench. The first Australians must have crossed at least ninety kilometres of water to reach their new home.
The passage may have been difficult, but the genetics of today's aboriginals suggest that it was made by many people. Native Australian DNA, like that of Papuans, is quite diver
se. There must have been many founders, with several incursions into the continent. Once they got there, the new inhabitants found their home congenial and, at least in the tropical north, tended to stay put. As a result, in today's Papua New Guinea, local populations are quite different from each other, with distinct 'clans' of mitochondria! lineages, each limited to a few remote mountain valleys. Their denizens stayed isolated until the first Europeans reached the interior half a century ago. They were in their own way advanced, and cut down trees to allow the tastier plants beneath them to grow. Hidden in their fastnesses for tens of thousands of years they remained insulated from the economic strife and the waves of movement that affected the rest of the world.