Homo Britannicus

by Chris Stringer

  Chris Stringer invited me to join the AHOB project in 2002. I submitted a proposal for a study of stable isotopes that was approved by the other team members. Stable isotope analysis is one of the few methods that can give us direct measures of people’s diets in the past. For the project I have mostly worked on carbon and nitrogen isotopes found in collagen, the organic content of bone. Like DNA, collagen degrades, so after about 100,000 years there isn’t much left. But the little that remains has great potential for revealing what people and animals ate over their whole lifetimes, and in what general proportions. It’s a relatively new area of research, and very exciting.

  We also developed novel techniques for measuring oxygen isotopes in fossil bone and teeth, and are still applying these methods to AHOB material. This, combined with carbon and nitrogen analysis, can be used to determine past climates. The oxygen work was mainly undertaken by Vaughan Grimes, a Bradford PhD student funded by AHOB.

  Most of the carbon and nitrogen in bone collagen comes from food the individual ate. The ratios of the stable isotopes of the two elements can be used as ‘signatures’ that provide a record of long-term diet. We can tell if the diet was mainly based on protein from the sea or land, and also whether the protein was mainly derived from animal or plant sources. Previous research, using these methods, had told us that European Neanderthals were carnivores at the very top of the food chain. Research I’ve done for AHOB on contemporaneous and more recent modern humans indicates that they had a similar diet, but also consumed aquatic resources, especially fish. There is no evidence indicating that Neanderthals ate any significant amounts of fish, so this may be a uniquely modern human adaptation in Palaeolithic Europe.

  We also looked at two late Upper Palaeolithic British sites, Gough’s Cave and Kendrick’s Cave, that date to around 14,000 years ago. The people at Gough’s ate mainly the meat of herbivores such as cattle and deer. There are lots of horse remains at the site but, surprisingly, the humans probably weren’t eating them. The human bones at this site had cut marks and were deposited with butchered animal bones. So perhaps the people living at Gough’s Cave did eat horse, but the human remains we’ve found belong to people who were killed and brought to the cave by its inhabitants. Our work on Kendrick’s Cave showed that about 30 per cent of the food eaten by these people came from the sea. High nitrogen isotope values indicate that they ate marine mammals such as seals. This is fascinating and provides some of the earliest evidence for the significant use of marine mammals by humans.

  AHOB’s main achievement, from my perspective, has been the multidisciplinary nature of the project, which has brought together researchers from different fields for a common aim. It has helped us improve our methods of working on isotope analysis of very old material. In the future I would like to focus on extracting proteins other than collagen from bones and teeth that might survive longer than 100,000 years.

  IAN CANDY

  Ian Candy is another expert in stable isotope analysis, as well as in uranium-series dating and Quaternary sedimentology. To many of his colleagues, his methods may seem more like sorcery than plain old science. But by working his magic, Ian has been able to reconstruct Britain’s past climates in extraordinary detail.

  I first became interested in Quaternary geology while studying geography at Royal Holloway, University of London. After I graduated, I stayed on to work for Jim Rose, who later brought me onto the AHOB team. The ancient river deposits that I looked at in eastern England have subsequently become key sites for the AHOB project. I went on to do a PhD looking at terrestrial carbonates in southern Spain. Coincidentally, this work too has had a significant impact on AHOB research. My work for AHOB has focused on investigating what stable isotopes can tell us about ice age rainfall and temperatures. The stable isotopes come from carbonates (limestone), which are minerals created by natural processes. The carbonates I’ve studied for AHOB come either from mollusc shells or are formed in soils, ground water, or in association with springs, called tufa.

  Soil carbonates form as small nodules, about 2–3 centimetres long. The nodules are produced only under certain climatic conditions, so their presence tells us something about the climate at the time. As carbonates are extremely soluble, they don’t accumulate in wet conditions, forming only where there is either low rainfall or very seasonal rainfall with long dry periods. In modern-day Europe they are restricted to some southern and eastern areas. In Britain, where rain falls throughout the year, all the carbonates in a soil are dissolved and washed away.

  When I first found soil carbonate nodules in fossilized soils in Britain, I recognized them from my work in Spain. They immediately told me that the environment of the time had different rainfall patterns from today. That’s why carbonates are so useful – insect and fauna studies can tell us about temperatures but they rarely reveal anything about precipitation. The analysis of soil, ground water and spring carbonates involves three processes. First, I log the carbonates in the field by drawing and describing how they occur in the sediments. This gives vital clues to the way in which they formed, that is within a soil profile or at the groundwater table. Next, I take the nodules to a laboratory and cut them into thin sections. I impregnate one section with resin, to make it hard. I then cut the section in half with a circular saw, polish the cut face, stick it to a piece of glass, and grind it down to a thin layer.

  Under a microscope I can see structures within the nodule not visible to the naked eye. The shape and size of the crystals that form within a soil carbonate will be very different from those that form within a groundwater carbonate. Microscopic analysis, therefore, allows us to establish the nodule’s origin and to identify evidence for alteration that may have occurred after the nodule formed.

  The final stage is isotopic analysis. Isotopes are species of elements that have different atomic weights. Because of this weight difference, natural processes selectively uptake the lighter isotopes. In soil carbonates, for example, the ratio between oxygen isotopes (16O:18O) is controlled by temperature, along with other variables, whilst the ratio between carbon isotopes (12C:13C) is controlled by the composition of the overlying vegetation. Isotopic analysis can, therefore, give us important information on the climatic and biological processes operating at the time the isotopes were formed.

  I conducted an in-depth investigation at Pakefield and found that the soil nodules are particularly enriched in 18O, indicating very warm temperatures and/or seasonal dryness. Pakefield is the earliest site of human occupation in all of northern Europe, and one of AHOB’s most exciting ventures, so information about its climate is critical. We now have fantastically detailed information about both temperature and rainfall, thanks in part to the analysis of the soil nodules. In combination with the plant and animal evidence they showed that there was a Mediterranean-type climate, with a strongly seasonal precipitation regime – wet winters and dry summers. It is thought that humans lived in the Mediterranean regions of Europe for a long time before they migrated to the relatively cold north. Now we know that humans colonized northern Europe quite early, but at a time when the north enjoyed a warm climate that they were adapted to and would have found comfortable. This makes sense, and allows a new interpretation of the early appearance of humans in Britain.

  I’ve also done a lot of work on the Hoxnian interglacial, an episode with a large number of occupation sites. I compared soil, ground water and tufa carbonates across the sites and found that the oxygen isotope ratios were not that dissimilar to the present day, although slightly heavier, possibly indicating a somewhat warmer climate.

  Something else I hope to pursue in the near future is a dating strategy that involves earthworms. Dating is often a problem because of the lack of suitable material. Earthworms might be able to help: as they move through the ground, digesting soil, they precipitate carbonates as little granules, about 1–2millimetres in size, which are excreted into the soil where large amounts accumulate. We’re trying to develop a technique to date these
deposits using uranium-series dating. If that were possible it would offer an amazing opportunity to accurately date sites of human occupation, because of the ubiquity of earthworms. At the moment, we have no idea how well it might work, but I’m keen to find out.

  Working on AHOB, with people who know the sites and the material so well, has been incredibly exciting. Quite often the archaeologists or mammal specialists will be sieving material from their sites and they’ll alert me to material I wouldn’t have known about otherwise. It’s wonderful to have access to material from so many important sites.

  My priority now is to develop new techniques with which to date and reconstruct the climates of a range of sites. AHOB has provided the opportunity to start research that, in the future, could lead to some really big advances.

  RUSSELL COOPE

  As well as the core members of the Project we have met above, we also have sixteen associate members, who are our closest collaborators. I’ve chosen just one of these to show how important they are, too. As perhaps the world’s leading Quaternary palaeoentomologists, there are few people who know more about fossil insects than Russell Coope. From a rambling farmhouse in the remote Scottish Highlands, Russell makes detailed reconstructions of Britain’s ancient environments and climates by studying these fascinating animals.

  I have been studying Quaternary insect fossils for over fifty years. I started work on them almost entirely by accident. I was washing mud off mammoth and woolly-rhino bones, when I discovered that it contained large numbers of beautifully preserved insects, mostly beetles. Very few people had done any systematic work on these fossils and I was immediately hooked.

  The mud that most archaeologists shovel up and barrow off the site I take home because it contains real treasures. Beetles tend to be large and robust, rather like entomological tanks, so they make excellent fossils and objects for study. I started off assuming that because the beetles were associated with extinct animals, they would also be extinct. Some time later, I realized that almost all of them were still living today. During the Quaternary their rate of evolution seems to have been incredibly slow; some of today’s species were living more than a million years ago and, in the beetle world, one million years represents one million generations. So there was plenty of opportunity for evolution, but for some reason it didn’t happen, at least in the features we can observe in the fossils.

  To identify fossil beetles I compare them with well-authenticated modern specimens. Their complexity means that I can often identify them to the species level. The most exciting fossils, though, are those which are highly distinctive but do not match any familiar species. When that happens, I widen the search to include distant international collections and literature. One memorable example is a highly unusual dung beetle that was abundant in the British Isles during the middle of the last Ice Age. The identity of this beautiful animal, which sports a large distinctive horn, split into two, in the middle of its head, remained a puzzle for more than fifteen years. As it often does, the solution came by accident. One day, while idly browsing the beetle collections in the Natural History Museum, I found four identical specimens. The label on the pins read, ‘Dingri, 10,000 feet, 1925 British Everest Expedition’. To find that a Tibetan dung beetle once inhabited Ice Age Britain was indeed a surprise.

  My growing involvement with Quaternary beetles led me to realize how useful they are as indicators of past environments. Beetle species are extremely fastidious about where they live and what they do for a living. So if the fossil species have the same environmental requirements as their modern descendants, I can reconstruct the environment they lived in.

  We know that ancient beetles required the same environmental conditions as their modern counterparts because of the way assemblages have remained constant. Whole suites of beetles from the British Ice Age still live in association with each other, often thousands of miles from where the fossils are found – some are now found in the high Arctic and some on the Siberian tundra. As temperatures changed, each species moved separately, tracking the acceptable climate across continents. After their forced marches the species reassembled in familiar associations in their new locations. An evolutionary explanation for this phenomenon is so unlikely that it can be discarded.

  The great significance of this is that fossil beetles can give precise indications of ancient climates. The majority of species are ‘hard wired’ with strict thermal requirements, so their presence allows an accurate reading of past temperatures. To take that reading, I use the Mutual Climatic Range method. This plots the present-day range of each species on climate space whose limits are defined by temperature gradients rather than latitude and longitude. In this way, geographically disparate species that live in similar climates, for example animals from cold northerly latitudes and those that live at altitude further south, can overlap in the same area of climate space. By investigating this overlap, I can calculate historical temperatures with surprising accuracy. Mean July temperatures can often be estimated to within two or three degrees. Winter temperatures are often more difficult and less precise, perhaps because the animals hibernate and are less affected by their thermal environment during these months.

  As well as climate, fossil beetles tell us about their local habitat. There are some water beetles that are entirely dependent on running streams, and others which need stationary water. Some water beetles are carnivorous, while others eat decomposing vegetation. Their terrestrial counterparts include carnivores, reed-eaters, tree-eaters, dung feeders, beetles which eat only fresh carcasses, beetles which eat only dry carcasses, and others which eat only the maggots which eat the carcasses, and so on down the food chain. Together, the beetles enable me to create a mosaic picture of their ancient environment.

  I became involved with AHOB because many of my insect faunas are associated with evidence of human occupation, so the palaeoenvironmental evidence they provide has significance for understanding past living conditions. Over the years I naturally found myself working with various members of the AHOB team. They have proved most valuable contacts and enjoyable company. The project itself has been great fun. As a corporate effort, it is possible to analyse ancient history in much more depth, and it’s always more exciting to look at the whole picture, not just the minutiae. The beetle assemblages are important because they can often yield environmental information that cannot be deduced from other fossil evidence.

  The Lynford site provides an excellent example of the unique contribution that the study of beetle assemblages can make. Enormous numbers of dung and carcass beetles were found here in association with the bones of large herbivorous mammals, chiefly mammoths, alongside numerous flint tools and flakes. There can be little doubt that both Neanderthals and mammoths were occupying this site at the same time. The beetles testify to the presence of vast quantities of dung, and indicate that the site was occupied during the summer months. The temperatures were comparable to present-day Siberia so life cannot have been easy. The beetles also show that after this period the climate became savagely cold with winter temperatures dropping below –20°C, but it is not known if humans were present during this period.

  The beetle assemblage from Pakefield, the oldest known site of human occupation in Britain, is also very informative. I found both running-water and stationary-water beetles, indicating a river characterized by rapids and pools, meandering across a flood plain. There’s also a highly specialized beetle that lives only on the submerged, decomposing trunks of oak trees, suggesting that the riverbanks were lined by large trees. Carcass- and maggot-feeding beetles suggest that large mammals were also present. Despite the site being on the coast today, there is no evidence of any salt marsh species, suggesting the sea was not that close 700,000 years ago. Interestingly, some of the species from Pakefield are now exclusively southern European. The Mutual Climatic Range indicates mean July temperatures of 17–23°C. The climate was several degrees warmer than the present day and more Mediterranean in character.

&n
bsp; Beetles have also shown us that climates can change extremely rapidly, even without human intervention. About 15,000 years ago, as the last glaciation was drawing to a close, Britain’s climate warmed dramatically. Mean July temperatures rose by 7°C in such a short time that I can’t measure it precisely, but the whole rise probably occurred during the span of one human lifetime.

  Finally, I must admit that one of the driving forces behind my work is the fact that beetles are stunningly beautiful animals. Even fossils dating from the start of the Pleistocene retain their vivid colours under the microscope. Species move on a vast scale, so there is the excitement of the hunt for them in far-flung exotic locations. From the scientific point of view, the main thrill of working with them is that, since they represent species still living, I can ask them meaningful questions and, what is more, receive useful answers back. You can’t gain such precise information from more spectacular extinct animals, such as the woolly rhino or mammoth, because their environmental requirements can only be inferred. On the other hand, the reluctance of beetles to evolve or to become globally extinct means that they are less valuable as stratigraphical indices than are the rapidly evolving mammals.

  There is a well-known story in entomological circles that when the famous biologist J.B.S. Haldane was asked what he thought of God, he replied, ‘He must have an inordinate love of beetles.’ Haldane was referring to the sheer number of species, but we now know that there is so much more to them than mere diversity.

  Acknowledgements