Unlocking the Past

by Martin Jones

  What he needed to do was to find examples of the potential ancestors in each story–ancient European hunter-gatherers who would serve as indigenous ancestors, and early Neolithic farmers as part of the pioneer population advance. At London’s Natural History Museum, Chris Stringer found Sykes some indigenous hunter-gatherers from a limestone cave in Cheddar in the south-west of England. These caves retained many remnants of the hunters and gatherers who had sought shelter here several thousand years before the first cereals and domestic livestock reached Britain’s shores. Alongside the abandoned hearths and the disused flint points from spears and arrows, the bodies of some of their users remained. Sykes examined two of the human skeletons from the caves, 13,000 and 9,000 years old respectively, and was much reassured by what he found. They were more than plausible ancestors of those still living in the region today. He actually found individuals, living locally, who carried precisely the same control region haplotype as the unearthed hunter-gatherer who had lain at rest for so long in a nearby cave.

  The Cheddar cave individuals strengthened the argument for a local, pre-agricultural ancestry. What Sykes needed now was a group of pioneer farmers who corresponded with the population trickle that did get through, bringing with them the ideas and traditions of farming. One of the best candidates in the archaeological record for such a population movement is the so-called ‘LBK’ culture. LBK stands for Linear Bandkeramic, the linear banded pottery that characterizes a series of early Neolithic sites scattered across the loess soils of Europe north of the Alps. The sites share not only a particular form of pottery, but also a typical cluster of timber long-houses, a particular range of domesticated plants and animals, and even a characteristic set of weeds accompanying the crops. The acid loess soils are hardly the ideal place for the kind of bone preservation conducive to ancient DNA studies. By 1996 the Oxford group were looking for some of the first generation of farmers of temperate Europe to bring domesticated crops and livestock north of the Alps, in order to establish what haplotypes they had brought with them. They visited three sites, two in Germany and one in France, while these were being excavated, so that they could extract bones carefully and take them back to the lab. Of nineteen individuals examined, only three provided clear evidence of native, uncontaminated DNA, but these three were indeed interesting. In the stretch of the control region studied, one of the three followed the consensus sequence, while the other two displayed mutations at positions 16,069 and 16,126. This takes our LBK pioneer farmers out on to a particular limb of control region variation, precisely the same limb as that occupied by modern populations from the Middle East. The contrasts between the hunter-gatherer from Cheddar Cave and the LBK farmers seemed to resonate with Sykes’s and Richards’s account. There was indeed a gene flow from the south-east, linked with the spread of farming, and the Middle Eastern genes flowed most discernibly with particular populations, such as the LBK farmers. Among those who eventually turned to agriculture, the great majority of European farmers trace the larger part of their ancestry back to the likes of the hunter-gatherers from Cheddar Cave.

  The spread of the new farming resources was subtle and in many cases quite gradual. Most of those who learnt to till the ground and sow seeds were direct descendants of communities already living in the region, whose intimate knowledge of Europe’s varied environments their descendants carried through alongside their new farming skills. The last major swathe of human migrations across Europe had probably already happened.

  which were the great journeys?

  Cavalli-Sforza and Sykes have now reached an accommodation of each other’s models. Each has acknowledged the past complexity that can accommodate both data-sets. An easy way of presenting the debate that went on between them is as a contest between two conflicting ideas. One highlighted a swathe of ancestral farming journeys, transforming demography, culture and language on a massive scale. The other emphasized people who doggedly stayed put, picking up new ideas and lifestyles, but barely moving a stone’s throw from the ancestral cave. That would be a misrepresentation. The work of Sykes and several others who have combined modern and ancient DNA studies has identified a variety of journeys. However, they are journeys that vary considerably in scale. Some involve the wholesale colonization of an unpopulated continent or island group. Others involve intermediate trickles across Europe or along the Nile corridor. Then there are the uncharted exploits of a few South Sea whalers. These journeys also vary considerably in how they match up, or indeed how they often fail to match up, with the parallel movement of ideas, language, material things and ways of life. Global patterns there may be, in material culture and genetics alike. However, when we unpack those patterns and attempt to trace particular lineages in detail, we do not see great convoys. We do not encounter pioneer settlers, on horseback and in sea boats, carrying with them blueprints for establishing whole new ways of living, while the previous occupants fade into oblivion. We see instead a complex assortment of meetings, melting pots and mixtures, people changing the way they do things, and embarking on smaller journeys that map directly on to neither language nor culture.

  How much is this busy picture in conflict with the smooth clines of Cavalli-Sforza’s grand synthesis? His principal components analysis did not paint a picture of unbounded complexity; there clearly have been significant and coherent trends in global gene flow, and those require an explanation. None the less, a trend is not a migration, an expansion or a journey. It is instead a pattern that emerges from a series of processes that deviate from randomness in a convergent manner. For example, the north-west to south-east cline in European genes indicates an axial trend in gene movement, but there is no necessity to conclude that this is the consequence of a single episode. It could result from very many movements in both directions, brought together by a shared axial tendency. While the mitochondrial control region may show the great variety of movements in the human past, Cavalli-Sforza’s gene maps indicate how in the longer term those movements converge upon particular trends. These trends can furthermore be related to parallel trends in language and material culture. Indeed, if we go back to look closely at the original use of the demic diffusion model by Cavalli-Sforza in the 1970s, we find there is no need for them to imply coherent migrations in any form. The outward movement of genes is an emergent consequence of a constellation of random trajectories, not of any sustained journey along a particular path.

  afterword

  The charting of great journeys has continued. New paths have been traced and the more familiar journeys have been further characterized; we now know considerably more about the genetic makeup of certain Linear Bandkeramic farmers, and can now go much farther than tracing their geographical ancestry to considering their lives and their health. A whole range of subsidiary journeys have been following up; there are biomolecular studies of the origins and movements of Anglo-Saxons, Vikings, Celts, Huns, Lombards, Jews, Mongolians, Bantu, Khoisan, and several other ethnic groups besides. In these studies, stable isotope analysis has come to prominence alongside DNA studies. While the latter offers models of the broad population ancestry and geography, the stable isotopes of a number of elements can distinguish the origins of food and water consumed at birth from that consumed later in life, by focusing on different parts of the skeleton. In this way, the lifetime movement of individuals can be charted against the population movement backcloth drawn from the genetic evidence.

  So we have fuller, more detailed maps, with very many more arrows, marked up with informative cultural labels. Beyond a proliferation of labelled arrows, we may observe something else. The concept of a ‘great journey’ is closely akin to that of a ‘main branch’ on the phylogenetic tree. The origin of the branch can be clearly seen, as can the trajectory of its crisply defined emergent branch. Those phylogenetic trees were at their most clear when based on a particular sequence with a simple pattern of evolution, for example a section of the mitochondrial control region. On reflection, we might conclude that the simplici
ty of the tree was an artefact of the simplicity of the data source. It is also an artefact of the method itself, which was designed to generate output of parsimonious form. It is a recurrent theme of these afterwords that with the move from single sequence analysis to genome-wide surveys, we have seen something of a fractal disaggregation of these clean branches into bushier clusters of smaller branches, with boundaries that are variously porous, and to varying degrees displaying reticulation. In more recent publications reporting biomolecular studies of past great journeys, a much used word has been ‘admixture’.

  Something similar has been happening to the cultural labels attached to those branches. In the early days of DNA science, the labelling of the branches of the human family tree with ‘cultures’, ‘ethnic groups’, or ‘races’, seemed relatively unproblematic. Since that time, anthropologists have more and more thought of these labels as culturally delineated and affirmed. The notion of ancestry is one among several resources which also include material culture, rituals and language with which those labels are actively applied. When a concept such as ‘ethnicity’ is approached with more attention to ambiguity, mutability, and porosity, these changes are resonant with what has been happening with phylogenetic trees. Those parallel elements are actually making studies of ethnicity and culture through time more interesting.

  Take the example of the Jewish Diaspora that followed Nebuchadnezzar’s destruction of the Temple in Jerusalem in the sixth century, BC. Much of that diaspora is recorded in great detail in historical texts; its chronology, geography, and its cultural conventions. One of these conventions holds that Jewishness is passed down the maternal line. From this we can build a hypothesis that an East Mediterranean origin will show up in the maternally inherited mitochondrial DNA of Jews dispersed across Europe. Indeed a series of studies have now borne that out. Over the last two millennia, the same maternal inheritance is discernible in both genes and culture.

  However, what makes this result interesting is not how good that fit is, but how there isn’t always the same fit. Jewish communities that for centuries lived in Northern Ethiopia prayed in synagogues, read the Torah and followed the strict dietary rules laid out in the Book of Leviticus, and respected the Sabbath, Passover and other Jewish feasts. The feast of Hannakah (which commemorates events from the second century, BC) is not known, which some have taken as an indication that the journey to Ethiopia predated that.

  How these Ethiopian Jews related to their own parents and children on the one hand, and to non-Jewish families on the other (and of course how non-Jewish families have related to them) has been the focus of a number of genetic studies. While some studies have detected a contribution from Near Eastern Jews, the relation clearly doesn’t mirror that of Europe. There is neither the evidence of reproductive separation from neighbours, nor of the emphasis on the maternal line. Gil Atzmon and colleagues, examined Indian Jews, which also fail to mirror the European model argue:

  Admixture with surrounding populations had an early role in shaping world Jewry, but, during the past 2,000 years may have been limited by religious law as Judaism evolved from a proselytizing to an inward-looking religion.

  We begin to see the communities themselves interacting with their own ‘great journeys’ and cultural stories of ethnic origin. In some cases, ethnic affiliation is built and legitimated in other ways, for example through power over land or commitment to a divine creed. One could argue this for certain episodes of the Roman Empire and of European settlement in the New World. In other cases the narrative of origins and great journeys retains and affirms its central role in building ethnicity; reproductive boundaries are closely regulated as are relations between generations. Each pattern leaves its own genetic fingerprint. The recent work on Jewish communities has shown how those patterns can fluctuate over time and space within a single cultural form.

  One recent example of such regulation in extreme form has been the apartheid regime in South Africa. The geneticist Mark Thomas, who had worked on several lineages, including Jewish lineages, turned to the Y-chromosome patterns observed in living populations from Central England. In these he noted some resonances with the South African pattern. A prevalence of Y-haplotypes correlating with those from Denmark and North Germany is plausibly associated with Anglo-Saxon settlers. Although previous researchers had suggested that the high level of their prevalence indicated a very sizeable population influx, Thomas pointed out the archaeological imprint for such that scale of influx was lacking. Either that scale relates to a serious underestimation of immigration numbers or, more likely as Thomas argues, a strict marriage regulation of an ‘apartheid’ form, sustained over several generations, protecting male lines and their assets.

  That inference was challenged by Australian Scientist John Pattison. Pattison made a number of observations, specifically about the model of an Anglo-Saxon incursion in the middle of the first millennium AD. First the labels ‘Angle’ and ‘Saxon’ are themselves far from culturally neutral, but unfold from within the origins narrative of such Anglo-Saxon scribes as the sixth century monk Gildas, as are those categories of ‘other’, ‘Welsh’ and ‘Briton’. Such narratives edit out much of the complexity of the identities involved, which probably comprised a mix of Angles, Saxons, Jutes, Franks, Frisians, and others. Pattison’s second point was that not only were the ethnic groups moving around less tightly bounded and homogenous, so were the periods of movement less tightly contained within any particular episode of time. It started before the migration period, and continued after. If we blur these boundaries of population and time period, Pattison argues a strong genetic signal can be generated, without the need for either massive historic influx or Apartheid-style restrictions that a single episode model requires. Whichever argument wins the day, what the approaches of both Thomas and Patterson display is a shift, over the past decade or two, from an empirical analysis of relatively simple trees to a foray into the richer and more complex forests of genetic evidence, equipped with explicit questions and explicit models.

  The Viking and Anglo-Saxon case studies each illustrate a strong European, perhaps a global, theme in the shaping of ethnic groupings, of the interplay between land and water. Water, or more specifically the navigable water’s edge, is a profound driver of human movement and consequently of the flow of genes. However else we may interpret phylogeographic patterns, they in part reflect the shallow water’s edge and the connections it opens up. So in following early farmers across Europe, we find that those pathways bifurcate along an inland river route, and a coastal route. As those pathways reach their Atlantic extreme, so particular stretches of water’s edge gain prominence in the movement of people and genes. These include the Atlantic Coast from Iberia to Britain, and the North Sea Basin, and a more northerly island chain linking parts the British Isles through Orkney and Shetlands to Scandinavia.

  At a certain point, we feel confident to attach ethnic labels to these watery movements, such labels as ‘Celt’, ‘Anglo-Saxon’, and ‘Viking’. It is certainly still possible to find publications approaching these labels as unproblematic categories, and bringing together cultural, linguistic and genetic evidence to narrate their unproblematic stories. It is also interesting to see research projects probing into that connection, aware that ethnicity building is a conscious and contested project. Its scribes and historians were actively simplifying the innate confusion of reality with a clear purpose in mind, and that purpose related to who was in, who was out, and who had power.

  The project of ethnicity building repeatedly shifted the focus from water to land. While some cultures, the Vikings are an example, retained a pronounced watery focus, the historian John Gillingham has implied that, as recently as the thirteenth century, it remained uncertain whether the future for my own ‘English’ ethnic identity might have the British Channel as its core or the British Islands as its perimeter, and some would argue the project was all the more challenging for aiming to absorb that banks the Humber rather than the banks
of the Loire. However attractive coasts, ports and boats, economic power repeatedly pulled the narrative to the agriculturally productive inland heartlands.

  As with much of the progress in molecular archaeology, we have moved from being able to tell simple stories, to address complicated ones. In the case of the great journeys, and how they connect to the myths of who are, and who we are not, those complications will continue to offer a most fruitful topic of research and debate.

  8

  beyond DNA

  the other molecules

  The molecule at the heart of life has cast a fresh light on past human lives. Its beam has ranged from pre-contact America, to the Nile Valley at the time of the classical civilizations, and further east to ancient communities in Siberia, China and Japan. It has shed light upon prehistoric farmers in Europe, central Asia and the Andes, and on the cereals and livestock on which they depended. That same beam has reached back in time, to Palaeolithic hunters and to a range of animals that have since been hunted to extinction. Further back still, it has illuminated the genetics of our extinct relatives, the Neanderthals. The glimpses we have caught of this genetic information allow us to look afresh at the movements of prehistoric peoples and their ancestries, and place their stories within a clear archaeological context and time scale. Their stories in the process become reworked and retold, and some of the complexity and detail of human lives is returned to them. But there is still much that is left in the shadows.