Unlocking the Past

by Martin Jones

  The general chronology of the spread of maize can be reassembled from finds of the cobs and grains. These show that it had arrived in the eastern United States by around 800 BC. This is the region in which the mound-building, metalworking Hopewell culture flourished from around 200 BC. It is an example of a ‘complex society’, the kind of society for which many have presumed cereal agriculture was a precondition, and the seeds provided evidence that it had been around for a few centuries before social complexity grew. However, possessing maize cobs is a very different thing from depending upon them. As Piperno’s study of the surface of ancient grinding stones has shown, there was more to the early farming food chain than maize alone. In the 1970s, Nick van der Merwe tested the notion of maize dependency by looking at the collagen isotopes from skeletons excavated from sites in the eastern United States. In skeletons of 5,000 years old, he recorded a carbon isotope signature typical of temperate zone foods, which is what we would expect, well before the appearance of maize in the region. When he moved to younger skeletons concurrent with the mound-builders, to many archaeologists’ surprise he found more or less the same signal. There was no sign of maize playing a major dietary role, even after it had been in the region for several centuries. It was not until AD 800, long after the mound-building Hopewell culture had waned, and a millennium and a half after the first maize in the region, that the C13 levels show a steep rise. In the region, this was the earliest sure sign of maize consumption on a large scale. Rather than stimulating and initiating the mound-building culture, the consumption of maize as a staple crop had actually followed it. What is more, the shift from maize as a dietary supplement to a major agricultural source did not seem to be particularly beneficial. In fact, the state of the bones themselves indicated the later peoples to be suffering from the narrowing of their diet from its greater diversity in Hopewell times.

  dissecting the diet

  Isotopic analyses can be employed to distinguish between herbivores and carnivores, between land-based and sea-based diets, and to pick up certain foodstuffs such as maize and the legumes. It has now become possible to go even further and to break down this dietary diary according to finer distinctions within the food chain. Let us return to Richard Evershed’s analyses of ancient lipids. He took advantage of a refinement in the GC/MS technique which allowed it not only to identify minute traces of ancient molecules but also to record their isotopic make-up. The dripping dishes that caught the fats from the spit-roast suckling pig provide an example of what this extra information can tell us. This refined technique allowed Evershed to measure the isotopic balance of the specific carbon atoms locked up in fats collecting at the bottom of those mediaeval roasting dishes. Pig stomachs fractionate carbon in a manner quite distinct from the ruminant stomachs of other domesticated herbivores. The distinctive pig signature matched perfectly the signature from the fats recovered from the dish, a useful corroboration of his interpretation. From other ceramic vessels he was able to go further and distinguish another animal product.

  Dairying plays a major part in the animal husbandry of the western world. In some cases it has lain at the centre of agricultural life, with milk, curd, cheese or yoghurt as the prime reasons for keeping animals in the first place. This, however, is not a universal practice. Many people in the world have difficulty in digesting milk. Moreover, it is not clear that dairying has anything like the antiquity of agriculture. Animals may have been domesticated for thousands of years before the practice of diverting milk from the animals’ young to the human food chain was introduced. There again our archaeological evidence has been shaky, dependent on the presence of artefacts tentatively identified as cheese-strainers, for example. It is an important and contentious issue in prehistoric agriculture. Some would argue that dairying was integral to farming from the start, and others would argue that it was a more recent, geographically restricted, phenomenon, resulting from a separate and distinct revolution in human ecology. While the artefacts were rather inconclusive on the issue, Evershed put his mind to discovering whether molecular evidence might resolve it.

  Distinguishing meat from milk from the same animal is not a straightforward task. The problem with many molecules found in milk is that they are also found in other tissues, including meat, and so cannot serve to separate the two. There are nevertheless some lipids that are much commoner in milk than in meat. They are distinguished by their relatively high proportion of short-length fatty acids. Evershed attempted to seek these out, but found that the shorter fatty acid molecules were significantly more likely to break down than their longer counterparts, badly skewing any ratio between the two in ancient material. At this stage, Evershed turned his attention to the isotopes, and found the differentiation he was after. If the same lipids are compared in milk and meat from the same animal, the milk lipids are distinguished from the meat lipids by a significantly lower proportion of the heavier carbon isotope. Again, by using GC/MS to target particular fatty acid molecules, and then assessing their carbon isotope ratio, Evershed found traces of milk in some of his mediaeval pots. He is now pushing the analyses well back in time, to establish conclusively when the practice of dairying began.

  a dietary diary

  The milk residue in an ancient pot may represent as little as a single meal. The collagen within our bones accumulates through life and records the average diet over a decade or so. We can extend the search to other parts of the archaeological record, for organic remains that record diet on other time scales. One such residue is hair.

  Whenever yuletide excess leads on to a January diet, then it should show up in my beard trimmings. Soon after Christmas they will be laden with heavy isotopes, as a succession of meat-rich meals work their way through my system. By January, a repentant intake of light salads will have significantly changed my beard’s isotopic composition. This will not be discernible in my bones. They will have merged the dietary signal of several years’ consumption, but our hair monitors short-term changes. A thread of shoulder-length or longer hair is like a dietary diary, with seasonal changes in nutrition recorded.

  Hair is composed of a tightly wound protein called keratin, the same substance of which wool, horn and feathers are made. A sizeable proportion of the keratin molecule is composed of an amino acid called cystine, which forms particularly strong bonds that endow keratin both with its durability and with resistance to decay. It does not take much to inhibit the fungi that normally decay hair. It may be the poisonous metal seeping from a lead coffin, or more familiar inhibitors, such as extremes of wet and dry. Ancient hairs can be found both free within an archaeological sediment, or still rooted to an ancient body. Some of the best preserved bodies that have featured in various chapters of this book have intact hair. Steve Macko from Virginia University decided these would provide a sharp and direct record of particular diets in the past.

  One opportunity for study came from an ancient traveller, frozen solid 5,300 years ago in the Tyrolean Alps. This ‘Ice Man’, or ‘Oetzi’ as he is locally nicknamed, set off high in the mountains, equipped with axe, bow and a sheath of arrows. Before hypothermia felled him, his eyes were presumably peeled for an ibex or a chamois–those mountain grazers, fragments of whose fur he used in his clothing. Some time after death, his hair became detached from his body and lay in tufts, caught up in his clothing. Macko took a few strands of that hair and tested them for their isotopic signature. He anticipated a fairly meaty signature, as everything about the man and his equipment suggested a hunter. Instead, the isotopes presented him with a surprising result.

  At the time of his frosty death, Oetzi’s hair displayed the isotopic profile found today not among hunters but among their complete antithesis, vegans. How could that have come about? What was a fur-clad vegan doing with bow and arrows high in the Tyrolean Alps? It was not a question that could be answered by the hair isotopes alone. Macko was only one of several researchers applying the new biomolecular methods to Oetzi’s body and paraphernalia. Konrad Spindler, the
archaeologist in overall charge, had read about the remarkable findings of an Australian researcher on the surface of stone tools. He wrote a short letter to Tom Loy, inviting him to come across to Innsbruck to inspect the finds.

  Oetzi’s toolkit provided Loy’s keen eye with a veritable feast of data and, yes, there was ample evidence the ancient man was a hunter. The bows, the arrows, and in addition the copper axe and stone knife all had the traces of blood Loy had come to recognize on stone implements from around the world. On the arrows, the traces of blood stretched back 30 cm along the shaft. These were big animals at the end of Oetzi’s line of sight. There were also fragments of hair and feather, and sheets of collagen adhering to several of the tools, all contributing to the picture of hunting, skinning and bone-working. Loy’s data seemed to clash with Macko’s. Yet there were some points of commonality.

  Adhering to the copper axe-head, especially around the haft and under the thong, were starch grains, the kind of trace that Piperno had encountered on Central American grinding equipment. From the manner in which they were distributed, Loy was able to speculate that Oetzi was rebinding the thong around his axe-head as he ate his last meal, a starchy meal of plant foods. Oetzi may well have been a seasoned and experienced hunter, his consumption of meat showing up in the isotopic pattern of his bone collagen. The strands of hair do not describe that life, but record a more transitory state, some time before his death, when he was consuming just plant foods, and perhaps lamenting his failure to bring down the prey he craved. We now know from fragments of meat fibre in his intestine that he eventually succeeded. It may indeed have been his desire for meat that took him to the perilous heights from which he failed to return.

  afterword

  In recent years, new proteins and lipids have been explored, and new stable isotopes understood. Some of the pace of transformation in DNA science has impacted on the other molecules; the field of genomics is now paralleled by the connected study of proteomics, whose potential is touched upon at the end of this afterword. In relation to our understanding of the human past, the principal advances of recent years have been in the integration of different forms of molecular evidence. Ways of bringing together analyses of the different molecules to address questions about our past are being constantly refined and improved. I shall illustrate this by returning to two themes from this chapter, potted histories, and a dietary diary.

  ‘Potted histories’ had once been intertwined with the history of agriculture; pottery and farming were almost synonymous. We are now familiar with farming being twice as old as pottery in some parts of western Eurasia, and being half as old as pottery in some parts of the east. The oldest ceramic vessels from East Asia may be 20,000 years old. If these very ancient pots were so much earlier than farming, what were they used for? Was it even for cooking?

  Oliver Craig, whose efforts to prise pottery away from adherent milk molecules were mentioned in the final chapter of The Molecule Hunt, assembled a team to address that question. They examined the lipids from inner surface residues of around 100 pottery fragments from thirteen Japanese sites, dating back beyond agriculture as far as 15,000 BP. What they repeatedly found was long-chain fatty acids associated with fish. They were, moreover, able to measure the stable isotope ratios of these lipids. These ratios displayed the isotopic enrichment expected from fish, and further allowed the discrimination between freshwater and marine fish, both of which were exploited. The Jomon cultures that made and used these pots also left behind vast middens of shellfish and bones, some of which remain as prominent features of the Japanese landscape today. The hunted animals, whose remains can be found in those middens, were most likely barbecued and eaten on the bone. However, the pioneering East Asian invention of pottery allowed cooking to extend to foods more easily consumed from a container, most notably fish. The ceramic pots thus played a key part in exploitation of rivers and seas, generating a human ecology of the Jomon Culture which lasted thousands of years, and stands as one of the most sustainable human ecosystems in our species’ history.

  Meanwhile, in Europe, a handheld diet of meats and breads prevailed, and pottery was not adopted until some time after the very first farms. A form that emerges quite early is a sieve rather than a container. In 2011, Mélanie Salque, working in Richard Evershed’s Bristol lab, examined a series of these ‘sieve pots’ that had been excavated from the Kuyavia region of Poland, in association with skeletal assemblages dominated by cattle bones. She detected lipids associated with beeswax, suggesting the sieves had been waterproofed prior to use. She also detected a range of animal-derived lipids, and measured their stable isotope value; her detailed findings pointed clearly to the use of wax-proofed sieve-pots for processing milk.

  The use of sieves to separate curds from whey is a familiar feature of cheese making, and it is certainly of intrinsic interest to learn of the great antiquity of cheese. The curds are propelled from the liquid matrix by a change in acidity of the milk, which can be achieved in a variety of ways. Those curds are fatty bodies, and the remaining whey aqueous with water-soluble contents. Among those contents is a sugar called lactose. Though quite similar to other sugars found in nature, it is sufficiently distinct to require its own enzyme—lactase—for digestion. Not surprisingly, young suckling mammals produce this enzyme in a large quantity, but soon reduce production after suckling has ended. Lactose consumed later in life will travel, undigested, to the intestine, providing a feast for microbes in unwelcome numbers. An overactive gut flora may just lead to flatulence, but can also make the consumer quite ill.

  If Poland’s Neolithic farmer just ate the curds, especially if those curds were then pressed to form a hard dry cheese, then the lactose would largely remain in the whey, which could be fed to other animals, such as pigs. The farmers would be relatively protected from the negative effects of lactose consumption. However, we know from analysis of modern populations that the majority of living Europeans are genetically encoded for lactase persistence; they continue to produce the enzyme throughout life, and can thus consume, not just the whey but even the fresh milk in quantity, and without negative consequences. That shift in the genetics of lactase persistence is rather similar to the shift in amylase copy number mentioned in the afterword to Chapter Five. Both are examples of the continued evolution of our human species still active today.

  These interconnections between food preparation, domestication, digestion, resistance, and genetics brought Mark Thomas from London, palaeogeneticist Joachim Burger from Mainz, and Biomolecular specialist Matthew Collins from York to discuss a new project to explore these interconnections through a range of molecular methods. The LeCHE project brought together many of the key players in the field, including Evershed. We saw in the afterword to Chapter Six that evolutionary inference had moved on from empirical examination of phylogenetic trees to explicit model building. A few years prior to the above study on sieve pots, Thomas had used a model building approach to make sense of the lactase persistence gene as seen in the world’s contemporary populations. From this he inferred an emergence of that gene by mutation around 7,500 years ago, in the general vicinity of the Hungarian Plain. Rather like the sieve-pots, that first spread of Linear Bandkeramic farmers was implicated. To test that hypothesis, Burger examined some prehistoric individuals. Of the individuals he was able to study, the earliest displaying the lactas persistence gene was a north German farmer who lived around 6,500 years ago.

  The many strands of the LeCHE project have followed the farmers and their animals from the Near East as they spread across Europe, charting their evolutionary, dietary and culinary histories on the way. Those farmers arrived in Europe using milk for cheese, and the whey for other purposes. The evolutionary advantage of extended consumption from cheese to whole milk is still a matter of debate. What is clear is that the advantage was considerable; the selection pressure in favour of lactase persistence was massive. That is the only way we can explain the current predominance in Europe and elsewhere of t
he gene over what is a rather short stretch of evolutionary time. Plentiful milk from the early farmers’ cattle herds may have been the principal driver to evolutionary success in Europe, not deleting, but certainly restricting the contribution of both lactose intolerant farmers, and also Europe’s hunter-gatherers from their the continent’s contemporary populations.

  The lactase story well illustrates how a number of molecular approaches may be productively brought together to explore the co-evolution of species on a millennial timescale. To illustrate a similar point, but on the timescale of an individual life, we can turn to the second theme of the dietary diary. In the year that Steve Macko published his work on hair as a ‘dietary diary’, three young bodies came to light on what is possibly the highest archaeological site in the world.

  Five or six centuries ago, a teenage maiden had been placed in a shrine, alongside two other children around half her age, twenty-five metres beneath the 6,739 metres summit of an Argentinian volcano called Llullaillaco. Her death seemed to have been quite peaceful. She had the appearance of deep sleep, there was no blood, and her intestines had not evacuated their contents. Her serene face was framed by long braided tresses of around two and a half years’ growth. An international team assembled by Andrew Wilson at Bradford was able to further explore the ‘dietary diary’ of the ‘Llullaillaco Maiden’.