Tens of thousands of traders travelled the weary route between China and Syria from the 1st century BC until the mid-14th century. Their goods, indeed they themselves, came from every corner of the known world: from India, Arabia, Siberia, Britain and the Baltic. The obstacles they faced - language, danger, physical hardship - hardly bear thinking about. Yet somehow they surmounted them so that their caravans of horses or of Bactrian camels could carry glass, tin, lead, coral, pottery and gold from the West; and incense, silk, muslin and spices from the East.
None of these traders, needless to say, had the faintest conception of the science that informs even the most basic modern worldview. But in other respects, they weren't so far removed from their 20th-century descendants. Like us, they were insatiable exchangers of ideas and information: the Silk Road has been referred to as "the Internet of its day", and without it modern civilisation could never have been born. They knew peace and war. From time to time they would witness, as we do today, a perplexing upheaval whereby a whole people migrates, willingly or not, from its ancestral land. They worked and bred and died. And, of course, they were created from the universal human blueprint of DNA, exactly like us.
Well, almost exactly. And that's where the scientists come in. The "Eurasia 98" project, from which these photographs were taken, has been the most ambitious undertaking in one of the world's newest scientific fields: genetic anthropology. Also known as molecular anthropology, this hybrid science is a kind of human archaeology, examining and comparing sequences of human DNA in order to find clues to ancient history.
Dr Spencer Wells, a 30-year-old research fellow at the Institute of Molecular Medicine at Oxford, is a pioneer of the method, and Eurasia 98 his most intriguing achievement. For five months of last year, Dr Wells (who was then attached to Stanford University in Massachusetts) led his team - from Stanford, Oxford, the University of California at Berkeley and the Uzbek Academy of Sciences - in the footsteps of the ancient silk traders, taking blood samples en route from some of the world's most ancient and least accessible peoples. The object was to trace their origins.
The team focused particularly on the middle section of the Silk Road, in the Caucasus, Central Asia and southern Siberia, between the steppes of European Russia and the Altai bordering Mongolia. More conquests and migrations have originated in these parts than almost anywhere else in the world. Scythians, Mongols, Parthians, Tartars, Turks, Persians, Kazakhs, Tajiks, Uzbeks, Kirgizs, Azeris, Kurds, Turkmens, Armenians - these are just a few of the peoples (many of them nomadic) who have held sway over these lands. There is barely a page in Western history that does not bear some trace - whether cultural or biological - of their influence. But despite the fact that these peoples now have descendants all over the world, there remain many groups at the heart of the Eurasian land mass - of, for example, Tajiks, Uzbeks, or Turkmens - which retain what some would refer to as "ethnic purity". These are pockets of people who have lived in the same place for centuries and who have jealously guarded their language, custom and collective sense of self.
For geneticists interested in ethnogenesis - the origins of racial groups - these conditions offer a fascinating range of possible lines of inquiry. On the one hand, DNA sampling for "pure" Tajiks - or Uzbeks, or Turkmens - will enable scientists to determine whether such groupings do indeed have distinct genetic profiles of their own. On the other, this will form a basis for providing comparisons with hypothetically related groups in other places and times.
At every town or village in which they stopped, the Eurasia 98 researchers would leap out of their Land Rover and use their combined linguistic and diplomatic skills to persuade up to 50 people in each location - all ostensibly from the same ethnic group - to give blood samples. And that, for the time being, was that, give or take a lot of sightseeing and human interaction. Months later, however, back in the laboratories of the West, they subjected these samples to DNA analysis using polymorphic genetic markers developed for the human genome project.
The details of the analysis process are complex, but in essence it involves isolating about a dozen small, highly variable stretches, or genes, of human DNA sequence and comparing those stretches in each of the samples taken. In the evolutionary short term (that is, over a period of about 1,000 years) people in whom these genes are identical are likely to share a common male ancestor. If your sample is wide enough, and you also have samples of similar sequences from archaeological findings - ancient skeletons or mummified bodies - then it is possible to trace the path of particular genes through the centuries, and end up with solid physical evidence of the geographical and historical origins of modern ethnic groups.
A certain amount of genetic research has already been done - for medical rather than historical purposes - on European, Middle Eastern, East Asian and Indian populations, but Central Asia, the historic link between all of these, has hitherto been what Dr Wells calls "a black hole in the genetic map". So key was the Silk Road to the intermingling of human populations that, without that link, few useful historical inferences could be drawn from the existing data. With it, the movement of particular genetic variations can be followed across the face of the earth and, by implication, through the centuries.
Eurasia 98 is merely the first step in a long journey towards that state of knowledge: much, much more data will need to be collected and analysed before the black hole can be filled. And some might argue that even when that journey is finished the answers it may give us - that the Basques may have originated in Siberia, say - will not significantly add to our sum of useful knowledge. But that would be to underestimate the significance of achieving even the smallest degree of certainty in an area of inquiry that has traditionally been very uncertain.
Humans have been categorising other societies for as long as they have known that other societies existed. Herodotus, the father of history, described some 50 different "peoples", many in this very region, most of whom he had heard about yet never encountered. But until now there has been no reliable way of defining those categories: every improvement in man's capacity to travel, communicate and intermingle has further complicated what, even 2,000 years ago, was a far from simple picture. Today we all know that different races exist, or have existed, and that they have sometimes moved dramati-cally across the continents. But how many of us could accurately define what a "race" is, and where one ends and another begins?
The history of the study of questions such as these is therefore a distinctly inglorious one, full of hazy concepts (Aryan, Caucasian, Homo sapiens africanus) and dubious sciences (craniology, eugenics). A "race" has been defined, with equal confidence, on the basis of certain physical characteristics, a language, a cultural practice or a religious belief - but rarely do all of these coincide in one person. (The groups sampled by the Eurasia 98 team were defined mainly by language and custom.) And even the most reputable students of such matters - variously known as cultural anthropologists, ethnologists, social anthropologists and ethnographers - have never wholly escaped from the "soft" end of the scientific spectrum. Like all social scientists, they are handicapped by the fact that their raw data represents only the tiniest, most arbitrary fraction of an interrelating system of cause and effect that is infinitely complex.
The best anthropologists may strive nobly for objectivity, but by the standards of objectivity and proof required in hard sciences they are all simply guessing. Sometimes they have little more basis for their opinions than amateur anthropologists who muse ignorantly in pubs on the meaning of phrases such as "ethnic Albanian". This lack of grounded knowledge has not prevented many of the most fanatical figures in modern history - from the 19th-century Europeans involved in the scramble for Africa, to Hitler, to Milosevic - from claiming a basis for their acts in allegedly scientific race theories. This emphasises the need for solid, irrefutable facts, and that is one reason why Eurasia 98 is so significant: it introduces an element of hard science into a discipline that has hitherto inclined towards the speculative and marginal. It does not supersede traditional anthropology, which will continue to draw its hypotheses from its traditional sources. What genetic anthropology does is provide - for the first time - the means for testing and proving those hypotheses.
There are two other reasons why Eurasia 98 is a project to be reckoned with. One is the modern, media-savvy way in which it has been organised. The youthful researchers set up a Eurasia 98 website, which they regularly updated from the field, and arranged television, radio and newspaper coverage to make their work accessible to as wide an audience as possible. They also took along a photographer, Mark Read, to make a pictorial diary of the journey.
This inclusive approach is interesting not only because it is increasingly used by researchers in all sciences (the more people you interest in your work, the more brains you can pick, and the more grants you obtain) but also because of its relevance to this particular line of inquiry. Mark Read's photographs enable us to look into the eyes of a host of different peoples, to see how their lives are different from and similar to our own, and to speculate about the connections between their lives and their ancestors'. Without these pictures, Eurasia 98's contribution to human understanding would be perceptibly less.
The other interesting thing about Eurasia 98 is that it has already confirmed one very significant hypothesis: that genetic variations from race to race are trivial compared with genetic variations between individuals within a race. In other words, in attempting to determine the biological origins of certain races, it has undermined the whole idea of "race" as a biological concept. That doesn't mean that the word is meaningless: anthropological concepts have value too, and many of the communities which co-operated with Eurasia 98 set great store by their sense of collective identity and history. But the lack of any significant biological proof of racial differences does make a nonsense of the rhetoric of the ethnic cleansers. "Of course there are differences between people," says Dr Wells. "Otherwise we'd have nothing to study. But the overwhelming evidence is that everybody is very similar to everyone else." This was brought home in a very personal way when one of Eurasia 98's American researchers, Nat Pearson, decided on a whim to submit a sample of his own blood for analysis. He found that it "matched" a sample in Samarkand, and was then able to meet the family from whom it came. The factual implication - a common male ancestor at some point in the past thousand years - was perhaps not all that surprising: most white Americans have European or Asian antecedents. But the incident did emphasise dramatically how much more of a family the human race is than we usually imagine.
"By studying the history book in these people's genes, and correlating what we find with archeological and historical data, we hope to fill a significant gap in our knowledge of this region," says Dr Wells. "But we also hope to extend our knowledge of the past in a wider sense."
Discovering who slept with whom a very long time ago - which is essentially what genetic anthropology is - may sound rather a frivolous pursuit. But anyone who feels that scientifically unfounded theories of race hold too much sway in the world will be grateful for any project which may eventually provide an objective means of distinguishing ethnic fact from ethnic falsehood. 2