You Are What You Eat
How a Tooth Can Reveal Where You Came from and What You Ate
Who Are You/Where Did You Come from?
A gruesome burial site was uncovered during road construction near Dorset, England in 2009. It contained the skeletons of 54 young men, with their heads separated from their bodies. There was no evidence of battle scars in other parts of the body, indicating that they had been executed. Radioactive carbon dating placed the deaths at about 1000 AD. No clothing or grave goods were found, so there was little information available as to who they were. Yet their identity is crucial in order to place this important burial in its correct historical context. Were they members of a local population or did they come from farther afield, and if so, from where?
Stonehenge is one of the largest and most important Neolithic (new stone age) monuments in the world. Its circular arrangement of standing stones is sited in dramatic isolation on Salisbury Plain in Wiltshire, Southern England (Figure 7.1). It was constructed over a period of 1500 years, between BC 3100 and BC 1600. The effort and organisation required for its construction, involving shaping, transporting and setting up the large and heavy stones are a cause of wonderment. Arguments abound as to the purpose of the monument. Theories range from it being used as a temple for religious purposes, an observatory for astronomical observations, a calendar to help compute the seasons, a retreat for the sick to heal, a place to worship ancestors and a cemetery to bury the (important?) dead. The arrangement of the stones appears also to provide the site with special acoustic properties that can amplify sounds.
Figure 7.1 The Neolithic site of Stonehenge in Wiltshire, England.
Although much is known about the physical aspects of Stonehenge, it is information derived from individuals found associated with it that gives it human interest and meaning. Great excitement always follows the discovery of a burial, especially if there are associated grave goods that may reveal features about the culture and status of the individual(s).
The richest burial to date was discovered in the village of Amesbury, about 5 km from Stonehenge. Like the Dorset burial site, the Amesbury burial was uncovered by accident when workers were laying the foundations for a new school. Dated to between BC 2400 and BC 2200, the grave contained the skeleton of a man about 40 years of age. Among the many valuable grave goods were 15 beautiful flint arrowheads (hence the nickname the ‘Amesbury archer’), boar tusks, copper knives and gold hair-decorations (hence the alternative name ‘King of Stonehenge’). Much information about the period has been derived from the origin of such grave goods, indicating the wide range of trade routes that existed at the time.
Despite all this treasure, perhaps the most important information that archaeologists wanted to know was where the archer came from. The simplest explanation would be that he was a chief who was born and lived locally. Alternatively, he may have come from Wales and been associated with moving the bluestones of Stonehenge that are known to have been quarried in the Preseli Hills, about 200 miles from Stonehenge. Could he have come from even farther afield? Each possibility would create a different personal history.
Another important burial near Stonehenge, on Boscombe Down, contained the skeleton of a 14–15-year-old boy, dated at about 800 years after the Amesbury archer. The grave contained a remarkable amber necklace with 90 beads (hence the nickname ‘boy with the amber necklace’). However, no evidence was forthcoming as to where he came from.
Towards a Solution to Mysteries 1 and 2
Due to their durability, teeth and bones are usually the only remains preserved from the distant past. Rarely are soft tissues found, except for animals buried in frozen ground, such as mammoths. In the case of fish such as sharks and rays, which lack a bony skeleton (their bodies being supported by softer cartilage), only the teeth remain from extinct species, leaving much having to be surmised about their evolution by studying living species.
Examination of any skeleton can provide general information indicating the species, its age, sex and the likely nature of the diet (i.e. whether it was carnivorous, herbivorous or insectivorous; see Chapter 4). In human skulls, the presence of tooth decay would indicate a sugar-rich diet. The question arises as to whether these hard tissue remains can reveal more detailed information.
To solve mysteries 1 and 2, there needs to be a feature present in the skeleton that will indicate where it came from. Surprisingly, there is, and the secret lies in the water that an individual drinks during life, for the water carries a unique fingerprint that can pinpoint where the individual lived. To understand the science behind it, it is necessary to know a little about the chemistry of water and how elements in the water end up in the teeth and bones.
Oxygen in Water
Water is made up of a mixture of the elements hydrogen and oxygen, and its chemical formula is the well-known H2O. This means each molecule of water has two atoms of hydrogen and one atom of oxygen. For our purposes, we need only consider the oxygen.
For any element, its atoms contain a number of subatomic particles in its central nucleus, including protons and neutrons. The number of proton particles is the same as the number of neutron particles. The two added together give the atomic number.
The main form of oxygen (O) has eight protons and eight neutrons, giving it an atomic number that can be written as 16O (Figure 7.2). This form constitutes over 99.7% of the total oxygen. However, there also exists another stable form of oxygen that is present in minute amounts (less than 0.2%). This reacts in the same way, but because it contains two extra neutrons, it is therefore heavier and is known as 18O (Figure 7.2). The different stable forms of an element are known as stable isotopes (as opposed to radioactive isotopes, which are unstable and break down; see page 110).
Figure 7.2 Diagram showing the nucleus of normal oxygen on the left (16O) made up of 8 protons (blue) and 8 neutrons (yellow). Its main stable isotope (18O) on the right is made up of 8 protons (blue) and 10 neutrons (yellow).
Drinking water is derived from water vapour evaporated off from the ocean, which falls from clouds as rain over the land. The heavier 18O isotope will fall sooner and therefore be more common in the drinking water associated with a warm tropical climate nearer the ocean. The lighter, main form of oxygen (16O) will be given off later at a further distance from the ocean and in colder climates towards the poles. The ratio of oxygen isotopes in the water varies according to latitude, water temperature and weather patterns. When someone drinks water, the oxygen isotopes in the water will be incorporated into their developing teeth and bones. Oxygen isotope levels for the majority of regions of the earth are known and are relatively stable with time (although corrective factors need to be applied to take account of climatic changes). By matching oxygen isotope levels in teeth and bones with the surrounding land, it is possible to determine where a person was born and lived. If there is a difference between oxygen isotope values of a specimen (especially when derived from enamel) and that of local specimens/ground where the skeleton was found, this implies migration from a different place of origin.
Structure and Composition of Teeth and Bones
Teeth and bones have two intermeshed components:
2. A soft but strong organic protein framework collagen, present in bone and dentine, which contains the elements nitrogen and carbon derived from the food. Enamel differs from bone and dentine in that it contains virtually all mineral and no protein.
The different elements making up the teeth and bones are all derived from the food and fluid the individual consumes.
Distribution of Stable Oxygen Isotopes in Teeth and Bones
When an individual drinks water, the two forms of oxygen (16O and 18O) are incorporated into the structure of the mineral crystals (in both phosphate (PO4) and carbonate (CO3) components) during the formation of the teeth and bones. The oxygen can subsequently be released experimentally from the tooth using acids and then accurately measured in a piece of apparatus called a mass spectrometer. The ratios of the oxygen isotopes can then be matched to places with similar values to discover where the individual originated from.
Due to the stability of the mineralised tissues over time following death, information can be successfully obtained from specimens millions of years old. Enamel (see Figure 4.2) is particularly useful as it is very stable and less prone to degenerative changes after death (diagenesis), such as demineralisation/recrystallisation and loss of collagen. This is due to enamel’s higher content of mineral (96%) and virtual lack of organic material (1% compared with 20% for dentine and 25% for bone). Bone, and to a lesser extent dentine, is more porous and more susceptible to change when buried in the ground following death due to its high content of collagen.
Solution to Mystery 1
With regard to the 54 skeletons uncovered in Dorset, at that time of burial England was being raided by the Vikings. In the case of the Dorset burial, analysis of the oxygen isotopes in the teeth showed conclusively that those young men were not locals but had originated from Scandinavia. The identity of the bodies as Viking warriors adds a whole new dimension to the context of the burial. This is one example where the generally successful Vikings came unstuck in their rape and pillage expeditions, and the whole group seems to have been captured and executed, presumably by the local Anglo-Saxons.
Solution to Mystery 2
When the enamel of the teeth of the ‘Amesbury archer’ (‘King of Stonehenge’) was analysed for oxygen isotopes, he was found not to be a local. In fact, his origin was much farther afield, from an Alpine region in central Europe that could be Switzerland, Germany or Austria. Although one mystery was solved, the information raised a host of new questions that may never be solved, such as why did he undertake such a long journey and why was he buried so close to such an important monument? When the new school near the site was opened in 2006, it was appropriately named the Amesbury Archer Primary School.
Oxygen isotope analysis from his teeth indicated that the boy with the amber necklace, like the archer, was not local but also originated from a considerable distance away. Unlike the Amesbury archer, who came from a cold, mountainous region, the boy came from a warmer, Mediterranean climate. These case histories indicate that, long into the distant past, Stonehenge already had an international clientele.
Having seen how the teeth and bones contain a unique fingerprint derived from drinking water that can tell where people (or animals) came from opens up the potential to solve many other important mysteries related to archaeology and evolution that cannot be answered by any other method.
Who Accompanied Christopher Columbus During His Second Voyage to America?
Isotope analysis of the teeth has the power to illuminate great historical events, one of which was the discovery (rediscovery?) of the New World of America by Christopher Columbus in 1492. This discovery also led to the establishment of the slave trade between America and Africa.
The skeletons of 20 individuals were recently unearthed at La Isabela, in the Dominican Republic, a place thought to be the first European town founded in the New World. Remarkably, there is strong evidence that these remains represent part of the original crew of Columbus’s second visit to the New World (1493–1496). As historical records of the crew were incomplete, could isotope analysis of the teeth help indicate the birthplace of the crew? It is known that Columbus had a personal African slave on his voyages of discovery.
Stable isotope values for oxygen, together with those of carbon and strontium (see later in this chapter), from the enamel of the teeth provided a totally unexpected result. There was strong evidence that not one but three of the skeletons were of individuals born in Africa. This view was further supported by the findings that some of the teeth showed intentional dental modifications (whereby the teeth had their shape deliberately altered by filing; see Chapter 16) typical of those occurring in West Africa. These new findings indicate that more native Africans were involved in the first documented explorations of America than previously suspected.
What Can Teeth Tell Us about the Evolution of Elephants, Whales and Sea Cows?
As oxygen isotopes in teeth and bones provide information concerning water in the environment, can they add flesh to the bones by providing us with crucial evidence of an animal’s environment that cannot be derived in any other way? For example, can it distinguish aquatic from land mammals? In the case of mammals such as whales, whose ancestors were land-dwelling creatures, can the teeth reveal when and who were the first ancestors that took to water?
In measuring stable oxygen isotope values in tooth enamel for different groups of animals, it has been determined that different values exist depending on whether the animal is aquatic (e.g. a whale), semi-aquatic (e.g. a hippopotamus) or terrestrial. Due to this important observation, data have been determined from the enamel in various fossils to determine whether they were aquatic, semi-aquatic or land based, with surprising results.
Elephants have previously always been considered land animals. Oxygen isotope values in the enamel of teeth were measured from two prehistoric elephants (Moeritherium and Barytherium) that lived over 37 million years ago. The results indicate that these ancestral elephants were not terrestrial but were semi-aquatic mammals, spending their days in water and feeding on freshwater plants.
Oxygen isotope values in enamel have also been investigated in 30–50-million-year-old fossils related to modern-day whales and sea cows (dugongs and manatees). The results indicated a different pattern in the evolution of the two groups. The early ancestors of whales were found to have inhabited freshwater environments, while their later ancestors moved rapidly into estuarine and marine environments. For the ancestors of sea cows, however, isotope values indicated an early transition to a marine environment without any evidence of an intermediate connection in freshwater habitats.
What Can Isotopes in Teeth Tell Us about the Life of Dinosaurs?
One group of animals that never fails to grip the imagination is the dinosaurs. These reptiles evolved 230 million years ago and were so successful that they were the dominant animals until about 65 million years ago, when the majority suddenly became extinct (except for modern birds now thought to be a form of dinosaur). The extinction is believed to have been related to a large asteroid slamming into the sea off Mexico’s Yucatan Peninsula (Chicxulub crater) and also the volcanic eruptions associated with the Deccan Traps of central India.
Although much can be learnt from the skeletons of dinosaurs, some important questions concerning their biology and behaviour are still poorly understood. Three of these are:
2. Did the large, herbivorous dinosaurs undergo an annual migration in search of enough food to live on (like living wildebeests today moving from the Masai Mara in Kenya to the Serengeti in Tanzania)?