Antiquitas saeculi juventus mundi (Ancient times were the youth of the world)
Francis Bacon
The surprising similarity of embryological genes in worms, flies, chicks and people sings an eloquent song of common descent. The reason we know of this similarity is because DN A is a code written in a simple alphabet - a language. We compare the vocabulary of developmental genes and find the same words. On a completely different scale, but with direct analogy, the same is true of human language: by comparing the vocabularies of human languages, we can deduce their common ancestry. Italian, French, Spanish and Romanian share word roots from Latin, for instance. These two processes — linguistic philology and genetic phylogeny — are converging upon a common theme: the history of human migrations. Historians may lament the lack of written records to document the distant, prehistoric past, but there is a written record, in the genes, and a spoken one, too, in the very vocabulary of human language. For reasons that will slowly emerge, chromosome 13 is a good place to discuss the genetics of genealogy.
In 1786 Sir William Jones, a British judge in Calcutta, announced to a meeting of the Royal Asiatic Society that his studies of the archaic Indian language Sanskrit had led him to conclude that it was a cousin of Latin and Greek. Being a learned fellow he also thought he saw similarities between these three languages and Celtic, Gothic and Persian. They had all, he suggested, ‘sprung from some common source’. His reasoning was exactly the same as the reasoning which led modern geneticists to propose the existence of the Roundish Flat Worm of 530 million years ago: similarities of vocabulary. For instance, the word for three is ‘tres’ in Latin, ‘treis’ in Greek and ‘tryas’ in Sanskrit. Of course, the great difference between spoken languages and genetic languages is that there is much more horizontal borrowing of words in spoken language. Perhaps the word for three had somehow been inserted into Sanskrit from a western tongue. But subsequent research has confirmed that Jones was absolutely right and that there was once a single people, speaking a single language in a single place and that descendants of those people brought that language to lands as far apart as Ireland and India, where it gradually diverged into modern tongues.
We can even learn something about these people. The Indo-Europeans, as they are known, expanded at least 8,000 years ago from their homeland, which some think was in the modern Ukraine, but was more likely in a hilly part of modern Turkey (the language had words for hills and fast-flowing streams). Whichever is correct, the people were undoubtedly farmers — their language also had words for crops, cows, sheep and dogs. Since this dates them to soon after the very invention of agriculture in the so-called fertile crescent of Syria and Mesopotamia, we can easily picture that their immense success in stamping their mother tongue on two continents was due to their agricultural technology. But did they impose their genes in the same way? It is a question I shall have to attack indirectly.
Today in the Indo-European homeland of Anatolia, people speak Turkish, a non-Indo-European tongue brought later by horse-riding nomads and warriors from the steppes and deserts of central Asia. These Altaic’ people owned a superior technology, too — the horse — and their vocabulary confirms as much: it is full of common words for horses. A third family of languages, the Uralic, spoken in northern Russia, Finland, Estonia and, bizarrely, Hungary, bears witness to a previously successful expansion of people, before and after the Indo-Europeans, using an unknown technology — herding of domestic animals, perhaps. Today the Samoyede reindeer herders of northern Russia are perhaps typical Uralic speakers. But if you delve deeper, there is undoubtedly a family connection between these three linguistic families: Indo-European, Altaic and Uralic. They derive from a single language spoken throughout Eurasia maybe 15,000 years ago by hunter-gathering people who had, to judge by the words in common in their descendant tongues, not yet domesticated any animals, except possibly the wolf (dog). There is disagreement about where to draw the boundaries that contain the descendants of these ‘Nostratic’ people. The Russian linguists Vladislav Illich-Svitych and Aharon Dolgopolsky prefer to include the Afro-Asiatic family of languages spoken in Arabia and North Africa, whereas Joseph Greenberg of Stanford University omits them but includes the Kamchatkan and Chukchi languages of north-east Asia. Illich-Svitych even wrote a little poem in phonetic Nostratic, having deduced what the root words sounded like.
The evidence for this linguistic super-family lies in the simple little words that change least. Indo-European, Uralic, Mongol, Chukchi and Eskimo languages, for example, almost all use or used the ‘m’ sound in the word for ‘me’ and the ‘t’ sound in the word for ‘you’ (as in the French ‘tu’). A string of such examples stretches to breaking point the coincidence hypothesis. Remarkable as it seems, the languages spoken in Portugal and Korea are almost certainly descended from the same single tongue.
Quite what the Nostratic people’s secret was we may never know. Perhaps they had invented hunting with dogs or stringed weapons for the first time. Perhaps it was something less tangible, like democratic decision making. But they did not altogether wipe out their predecessors. There is good evidence that Basque, several languages spoken in the Caucasus mountains and now-extinct Etruscan do not belong to the Nostratic super-family of languages, but share an affinity with Navajo and some Chinese tongues in a different super-family known as Na-Dene. We are getting into highly speculative ideas here, but Basque, which survived in the Pyrenees (mountains are backwaters of human migration, bypassed by the main flows), was once spoken in a larger area, as shown by place names, and the area coincides neady with the painted caves of Cro-Magnon hunters. Are Basque and Navajo linguistic fossils of the first modern people to oust the Neanderthals and spread into Eurasia? Are speakers of these tongues actually descended from mesolithic people, and surrounded by neighbours of neolithic descent speaking Indo-European languages? Probably not, but it is a delicious possibility.
In the 1980s Luigi Luca Cavalli-Sforza, a distinguished Italian geneticist, watched these unfolding discoveries of linguistics and decided to ask the obvious question: do linguistic boundaries coincide with genetic ones? Genetic boundaries are inevitably more blurred, because of intermarriage (most people speak only one language, but share the genes of four grandparents). The differences between French and German genes are much less definite than the difference between the French and the German languages.
None the less, some patterns emerge. By gathering data on the common, known variations in simple genes — the ‘classical polymorphisms’ — and doing clever statistical tricks called principal-components analysis with the resulting data, Cavalli-Sforza uncovered five different contour maps of gene frequencies within Europe. One was a steady gradient from south-east to north-west, which may reflect the original spread of neolithic farmers into Europe from the Middle East: it echoes almost exactly the archaeological data on the spread of agriculture into Europe beginning about 9,500 years ago. This accounts for twenty-eight per cent of the genetic variation in his sample. The second contour map was a steep hill to the north-east, reflecting the genes of the Uralic speakers, and accounting for twenty-two per cent of genetic variation. The third, half as strong, was a concentration of genetic frequencies radiating out from the Ukrainian steppes, reflecting the expansion of pastoral nomads from the steppes of the Volga—Don region in about 3,000 BC. The fourth, weaker still, peaks in Greece, southern Italy and western Turkey, and probably shows the expansion of Greek peoples in the first and second millennium BC. Most intriguing of all, the fifth is a steep little peak of unusual genes coinciding almost exactly with the greater (original) Basque country in northern Spain and southern France. The suggestion that Basques are survivors of the pre-neolithic peoples of Europe begins to seem plausible.1
Genes, in other words, support the evidence from linguistics that expansions and migrations of people with novel technological skills have played a great part in human evolution. The gene maps are fuzzier than the linguistic maps, but this enables them to be subtler. On a smaller scale, too, they can pick out features that coincide with linguistic regions. In Cavalli-Sforza’s native Italy, for instance, there are genetic regions that coincide with the ancient Etruscans, the Ligurians of the Genoa region (who spoke a non-Indo-European ancient language) and the Greeks of southern Italy. The message is plain. Languages and peoples do, to some extent, go together.
Historians speak happily of neolithic people, or herdsmen, or Magyars, or whoever, ‘sweeping into’ Europe. But what exactly do they mean? Do they mean expanding, or migrating? Do these newcomers displace the people already there? Do they kill them, or merely out-breed them? Do they marry their women and kill their men? Or do their technology, language and their culture merely spread by word of mouth and become adopted by the natives? All models are possible. In the case of eighteenth-century America, the native Americans were displaced almost completely by whites — both in genetic and linguistic terms. In seventeenth-century Mexico, something much more like mixing happened. In nineteenth-century India, the language of English spread, as a whole procession of Indo-European languages such as Urdu/Hindi had done before, but in this case with very little genetic admixture.
The genetic information allows us to understand which of these models applies best to pre-history. The most plausible way to account for a genetic gradient that grows steadily more dilute towards the north-west is to imagine a spread of neolithic agriculture by diffusion. That is, the neolithic farmers from the south-east must have mixed their genes with those of the ‘natives’, the influence of the invaders’ genes growing steadily less distinct the further they spread. This points to intermarriage. Cavalli-Sforza argues that the male cultivators probably married the local hunter-gatherer women, but not vice versa, because that is exactly what happens between the pygmies and their cultivator neighbours in central Africa today. Cultivators, who can afford more polygamy than hunter-gatherers, and tend to look down on foraging people as primitive, do not allow their own women to marry the foragers, but the male cultivators do take forager wives.
Where invading men have imposed their language upon a land but married the local women, there should be a distinct set of Y-chromosome genes but a less distinct set of other genes. This is the case in Finland. The Finns are genetically no different from the other western Europeans who surround them, except in one notable respect: they have a distinct Y chromosome, which looks much more like the Y chromosome of northern Asian people. Finland is a place where the Uralic language and the Uralic Y chromosomes were imposed on a genetically and linguistically Indo-European population some time in the distant past.2
What has all this to do with chromosome 13? It so happens that there is a notorious gene called BRCA2 on chromosome 13 and it, too, helps to tell a story of genealogy. BRCA2 was the second ‘breast cancer gene’ to be discovered, in 1994. People with a certain, fairly rare version of BRCA2 were found to be much more likely to develop breast cancer than is usually the case. The gene was first located by studying Icelandic families with a high incidence of breast cancer. Iceland is the perfect genetic laboratory because it was settled by such a small group of Norwegians around A D 900, and has seen so little immigration since. Virtually all of the 270,000 Icelanders trace their descent in all lines from those few thousand Vikings who reached Iceland before the little ice age. Eleven hundred years of chilly solitude and a devastating fourteenth-century plague have rendered the island so inbred that it is a happy genetic hunting ground. Indeed, an enterprising Icelandic scientist working in America returned to his native country in recent years precisely to start a business helping people to track down genes.
Two Icelandic families with a history of frequent breast cancer can be traced back to a common ancestor born in 1711. They both have the same mutation, a deletion of five ‘letters’ after the 999th ‘letter’ of the gene. A different mutation in the same gene, the deletion of the 6,174th ‘letter’, is common in people of Ashkenazi Jewish descent. Approximately eight per cent of Jewish breast-cancer cases under the age of forty-two are attributable to this one mutation, and twenty per cent to a mutation in BRCA1, a gene on chromosome 17. Again, the concentration points to past inbreeding, though not on the Icelandic scale. Jewish people retained their genetic integrity by adding few converts to the faith and losing many people who married outsiders. As a result, the Ashkenazim in particular are a favourite people for genetic studies. In the United States the Committee for the Prevention of Jewish Genetic Disease organises the testing of schoolchildren’s blood. When matchmakers are later considering a marriage between two young people, they can call a hotline and quote the two anonymous numbers they were each assigned at the testing. If they are both carriers of the same mutation, for Tay—Sachs disease or cystic fibrosis, the committee advises against the marriage. The practical results of this voluntary policy — which was criticised in 1993 by the New York Times as eugenic — are already impressive. Cystic fibrosis has been virtually eliminated from the Jewish population in the United States.3
So genetic geography is of more than academic interest. Tay— Sachs disease is the result of a genetic mutation comparatively common in Ashkenazi Jews, for reasons that will be familiar from chromosome 9. Tay—Sachs carriers are somewhat protected against tuberculosis, which reflects the genetic geography of Ashkenazi Jews. Crammed into urban ghettos for much of the past few centuries, the Ashkenazim were especially exposed to the ‘white death’ and it is little wonder that they acquired some genes that offer protection, even at the expense of lethal complications for a few.
Although no such easy explanation yet exists for the mutation on chromosome 13 that predisposes Ashkenazis to develop breast cancer, it is quite possible that many racial and ethnic genetic peculiarities do indeed have a reason for their existence. In other words, the genetic geography of the world has a functional as well as a mapping contribution to make to the piecing together of history and pre-history.
Take two striking examples: alcohol and milk. The ability to digest large amounts of alcohol depends to some extent on the overproduction by a certain set of genes on chromosome 4 of enzymes called alcohol dehydrogenases. Most people do have the capacity to pump up production by these genes, a biochemical trick they perhaps evolved the hard way — that is, by the death and disabling of those without it. It was a good trick to learn, because fermented liquids are relatively clean and sterile. They do not carry germs. The devastation wrought by various forms of dysentery in the first millennia of settled agricultural living must have been terrible. ‘Don’t drink the water’, we westerners tell each other when heading for the tropics. Before bottled water, the only supply of safe drinking water was in boiled or fermented form. As late as the eighteenth century in Europe, the rich drank nothing but wine, beer, coffee and tea. They risked death otherwise. (The habit dies hard.)
But foraging, nomadic people not only could not grow the crops to ferment; they did not need the sterile liquid. They lived at low densities and natural water supplies were safe enough. So it is little wonder that the natives of Australia and North America were and are especially vulnerable to alcoholism and that many cannot now ‘hold their drink’.
A similar story is taught by a gene on chromosome 1, the gene for lactase. This enzyme is necessary for the digestion of lactose, a sugar abundant in milk. We are all born with this gene switched on in our digestive system, but in most mammals — and therefore in most people — it switches off during infancy. This makes sense: milk is something you drink in infancy and it is a waste of energy making the enzyme after that. But some few thousand years ago, human beings hit on the underhand trick of stealing the milk from domestic animals for themselves, and so was born the dairy tradition. This was fine for the infants, but for adults, the milk proved difficult to digest in the absence of lactase. One way round the problem is to let bacteria digest the lactose and turn the milk into cheese. Cheese, being low in lactose, is easily digestible for adults and children.
Occasionally, however, the control gene which switches off the lactase gene must suffer a mutation and the lactase production fails to cease at the end of infancy. This mutation allows its carrier to drink and digest milk all through life. Fortunately for the makers of Corn Flakes and Weetabix, most western people have acquired the mutation. More than seventy per cent of western Europeans by descent can drink milk as adults, compared with less than thirty per cent of people from parts of Africa, eastern and south-eastern Asia and Oceania. The frequency of this mutation varies from people to people and place to place in a fine and detailed pattern, so much so that it enables us to pose and answer a question about the reason people took up milk drinking in the first place.
There are three hypotheses to consider. First and most obvious, people took up milk drinking to provide a convenient and sustainable supply of food from herds of pastoral animals. Second, they took up milk drinking in places where there is too little sunlight and there is therefore a need for an extra source of vitamin D, a substance usually made with the help of sunlight. Milk is rich in vitamin D. This hypothesis was sparked by the observation that northern Europeans traditionally drink raw milk, whereas Mediterranean people eat cheese. Third, perhaps milk drinking began in dry places where water is scarce, and was principally an extra source of water for desert dwellers. Bedouin and Tuareg nomads of the Saharan and Arabian deserts are keen milk drinkers, for example.
By looking at sixty-two separate cultures, two biologists were able to decide between these theories. They found no good correlation between the ability to drink milk and high latitudes, and no good correlation with arid landscapes. This weakens the second and third hypotheses. But they did find evidence that the people with the highest frequency of milk-digestion ability were ones with a history of pastoralism. The Tutsi of central Africa, the Fulani of western Africa, the Bedouin, Tuareg and Beja of the desert, the Irish, Czech and Spanish people - this list of people has almost nothing in common except that all have a history of herding sheep, goats or cattle. They are the champion milk digesters of the human race.4
The evidence suggests that such people took up a pastoral way of life first, and developed milk-digesting ability later in response to it. It was not the case that they took up a pastoral way of life because they found themselves genetically equipped for it. This is a significant discovery. It provides an example of a cultural change leading to an evolutionary, biological change. The genes can be induced to change by voluntary, free-willed, conscious action. By taking up the sensible lifestyle of dairy herdsmen, human beings created their own evolutionary pressures. It almost sounds like the great Lamarckian heresy that bedevilled the study of evolution for so long: the notion that a blacksmith, having acquired beefy arms in his lifetime, then had children with beefy arms. It is not that, but it is an example of how conscious, willed action can alter the evolutionary pressures on a species — on our species in particular.