Patients of the past tell the story in their bones

When I was in primary school in the early 1960s, we learned Irish history from a book called A Class-Book of Irish History, by James Carty, MA (1900-1959). This book provided a grand (if partisan) sweep of Irish history from the Stone Age to the Anglo-Irish Treaty of 1921; the subsequent Civil War was too recent and too sensitive a subject to be included. However, the early ‘historical facts’ presented in our book were a bit off the mark too.

We were taught that various races – including Partholons, Fir Bolgs, Tuatha Dé Dannan and finally heroic Milesians /Celts – invaded Ireland and were the antecedents of the ‘real’ Irish people.

Descendants of later arrivals like the Vikings, Normans and Planters, although they had been living and intermarrying with the descendants of the earlier inhabitants for centuries, didn’t really cut the mustard.

What was not understood, not by me anyway, was that the prehistoric invasions we learned about were entirely fictitious, invented by the author of Leabhar Gabhála Érenn (The Book of Invasions) in the eleventh century. According to one version the first people to arrive in Ireland were led by Cessair, daughter of Bith, son of Noah who migrated to the western edge of the world to escape the oncoming flood. Repeated in the Annals of the Four Masters (1632-6) and Foras Feasa ar Éirinn (1634) these stories were accepted as conventional history by some for a very long time.

In reality the historical record in Ireland began in the fifth century A.D. with the arrival of Christianity and the adoption of the Roman alphabet. (Ogham writing is found only as inscriptions on monuments). The oldest example of Irish writing is the sixth/seventh century Cathach/The Psalter of St Columba, which is conserved in the Royal Irish Academy (RIA MS 12 R 33) in Dublin. Sources such as annals, law tracts, genealogies and the lives of saints provide insights into life in early medieval Ireland but tell nothing about the prehistoric era. Happily, other disciplines such as geology, archaeology and anthropology can help fill in the gaps with some amazing science.

The age of the Earth
In the seventeenth century, James Ussher (1581-1656), Archbishop of Armagh, using the Bible as well as Hebrew and Egyptian texts, calculated that world was created on 23 October 4004 B.C. In the eighteenth century, as the industrial revolution took off and coal mines and canals were dug, people noticed that rock strata contained fossils of ancient beings, indicating that the world was much older than previously thought. Different strata contained different fossils leading to the concept of ‘faunal succession’ – which would become an important method in understanding climate, geologic time, continental drift and evolution.

In the nineteenth century John Philips (1800-74), Professor of Geology at Trinity College Dublin, studied sedimentation to calculate the age of the earth – 96 million years. William Thompson, Lord Kelvin (1824-1907), assuming that the earth was originally a molten sphere, worked out how long it would take the surface to cool – 100 million years.

To Charles Darwin (1809-1882) these estimates seemed far too low to allow for the evolution of the diversity of plants and animals on the planet. From 1905 onwards radiometric dating, which uses the half-life of the radioactive decay of one isotope to another (such as uranium to lead) to calculate the age of rocks led to the currently accepted age of the earth – 4.54±0.05 billion years. Analyses of moon rock and material from meteorites indicate that the solar system also formed at this time.

Carbon-14
The timing of more recent events and materials can be estimated in other ways. Discovered by Willard Libby (1908–1980) at the University of Chicago in 1949, Carbon-14 (14C) dating is also a radiometric technique used to date carbonaceous material rather than rocks. Containing six protons and eight neutrons 14C is an isotope of carbon produced in the atmosphere by the action of cosmic rays on nitrogen. Unlike carbon’s other isotopes, 12C and 13C which are stable, 14C decays to nitrogen with a half-life of 5,730 ± 40 years. As carbon isotopes are absorbed into plants and animals during life all living matter contains a (very) small amount of 14C. But once an organism dies no more carbon is incorporated thus creating a time-capsule with a steadily diminishing 14C count.

Thus, the age of a material containing carbon can be estimated by measuring the amount of 14C present and comparing this against the known half-life of the isotope. Dates derived from 14C can be carried back about 50,000 years, after which time the isotope has completely decayed.

A more sophisticated method to determine the amount of the 14C isotope remaining in a sample uses accelerator mass spectrometry to count the actual number of atoms of the isotope present, rather than just the radioactivity emitted. This has allowed scientists to date material from the tiniest of samples.

Famously, using only a few fragments of cloth, scientists dated the Turin Shroud to 1260-1390 A.D. showing conclusively that it was not a representation of the body of Christ. In a remarkable Irish study, skeletons from a medieval burial ground unearthed during the construction of the N15 Bundoran-Ballyshannon bypass at Ballyhanna, Co Donegal were dated to a period from the early eighth century to the seventeenth century showing that the burial ground was used for almost 1,000 years.

The stable isotopes of elements such as hydrogen, carbon, oxygen, nitrogen, sulphur and strontium which do not undergo radioactive decay, can also reveal a huge amount of information about an individual’s past. As we grow the isotopes that are in the food and water we consume are incorporated into our tissues where they can be detected. By measuring the ratios of different isotopes in skeletal bone or teeth (for example δ18O) it is possible to determine a long-dead person’s diet and where geographically they grew up.

Dendrochronology
Trees start growing in the spring when the cells laid down are a light tan colour. In the autumn the cells are much darker and growth stops completely in the winter. So each year a tree grows one ring. The climatic conditions during growth affects the width of the ring; wet years result in wide rings and dry years in narrow rings. Thus a pattern of rings develops over the life of the tree. By overlapping the ring patterns of successively older trees a long sequence of patterns can be constructed reflecting growth over thousands of years.

A piece of wood from a medieval site can be accurately dated by looking at the ring pattern in the wood and comparing it to the known configuration. Thanks to bog oaks which survived for centuries in the Irish peat bogs, a 7,000-year-old tree ring chronology had been established for Ireland by the School of Archaeology and Palaeoecology at Queen’s University in Belfast.

The rings also reveal what the climate was like during the growth of the tree. For example, something happened around 536 A.D. to stunt the growth of trees for the next ten years. This was most likely a hemispheric dust veil from volcanic eruptions in 535/6 and again in 539/40; the ash from the volcano, thrown into the atmosphere, blocked solar radiation resulting in cold weather, crop failure, famine and disease.

Right on cue, in the early 540s the Irish annalists recorded mortalitas magna quae blefed dicitur (a great mortality which is called blefed) – analyses of skeletal remains in Germany have identified this disease as bubonic plague (the Plague of Justinian) which killed a huge percentage of the population of Europe and the Middle East.

Osteoarchaeology
Much information can be gleaned from studying skeletal remains. The sex and stature of adults, the growth of juveniles, and a range of pathological lesions may be recorded. A number of techniques applicable to forensic anthropology and archaeology are used to determine age at death. Age-related morphological skeletal traits can be determined macroscopically or radiologically.

For example, features such as epiphyseal closure and diaphyseal bone length are used to calculate the age of juveniles; assessments of the status of non-synovial joints and microscopic features of bone in cross sections indicate age at death in adults.

More recently, chemical and molecular biological methods such as protein racemization, telomere length analysis and the Maillard ‘browning’ reaction have been used in forensic anthropology, but their use in archaeology is limited. A statistical technique known as transition analysis – that creates a probability distribution for a number of anatomical features has recently improved age estimates for adults, and provided more realistic approximations of population-level mortality. Nonetheless, providing a precise age of death in older adults remains problematic.

The skeletal impact of disease and the presence of stressors in a community, such as malnutrition, illness or infectious disease, is well demonstrated by the findings of the Ballyhanna archaeological excavations. Rickets, osteoporosis, arthritis, avascular necrosis of the femoral head, injuries from trauma, tuberculosis and non-specific infections – evidenced by periosteal new bone grow – were all observed.

Analysis of teeth and the surrounding jaw bone can reveal some of the most interesting information of past lives. High levels of calculus point to a diet rich in protein and carbohydrate whereas caries are due to carbohydrate alone. Comparing the frequency of both can be used to assess the relative levels of protein versus carbohydrate in a population’s diet. In the pre-antibiotic era, dental abscesses, evidence for which is easily seen in a skeleton, were frequently fatal; possibly explaining why fracture of the tooth was top-of-the-list of the seven most important fractures in the old Irish law text, Bretha Déin Chécht.

Ancient DNA
Ancient DNA (aDNA) is another tool that is used to open windows on the past; the petrous temporal bone is a rich source of aDNA even in poorly preserved skeletons. Obvious uses are the identification of the sex of skeletal remains when it not possible to do so macroscopically, and to establish relationships between individuals. Amazingly, using mitochondrial DNA which is passed in the maternal line, a 42-year-old man in Somerset was found to have a common maternal ancestor with a 9,000-year-old skeleton known as Cheddar Man (from Cheddar Gorge, also in Somerset).

In 2012 a body found under a car park in Leicester in England was identified as that of King Richard III (1452-1485) who was deposed and killed at the Battle of Bosworth Field – making way for the Tudor domination of England and Ireland for the next 150 years.

Using genetic changes that occur at a steady rate over long periods of time, DNA can also be used as a molecular clock. For example, it has been estimated that there are 1.5-2 million mutational differences between Neanderthals and modern humans. Applying the mutation clock to this count suggests that humans and Neanderthals split from each other somewhere between 550,000 and 750,000 years ago.

The ancestry of modern populations can also be determined by haplotype analysis; a recent study by Byrne et al from Trinity College Dublin suggests that the Norse-Viking influence in Ireland was greater than previously thought. Diseases such as tuberculosis and plague have been identified from the DNA of the causative organisms found in ancient remains, and the DNA of plants and animals can provide insights into ancient diets and economies.

Other techniques
Many other techniques can also provide information on the world of the past. Palaeomagnetism examines the earth’s magnetic field, and the observation from rocks that the magnetic poles have flipped several times in the past is used to study past global plate tectonics. Luminescence dates crystalline materials such as quartz to the last time they were exposed to sunlight. Lichenometry measures the radial growth of lichens to determine the age of exposed rock.

Palynology and palaeoentomology, the studies of ancient pollen and insects, respectively, also provide information on past environments, diet and living conditions. Analysis of trapped air in polar ice cores reveals the composition of the ancient atmosphere while tephra deposits tell of ancient volcanic eruptions.

Finally, linguistic analyses which correlate well with DNA can also provide insights into population migrations and relationships; genetic and linguistic data show similar signatures of human population dispersal within regions. In summary, we have very many techniques available to us now to tease apart the long, rich and fascinating story of our past. In the fifty-year blink since I was school-boy we have come a long way, but so far no Partholons, Fir Bolgs, Tuatha Dé Dannan or Milesians have been discovered.

Further reading

• John Marra, Hot Carbon: Carbon-14 and a Revolution in Science (New York, Columbia University Press (2019).
• Nord, A.G., Billström, K. ‘Isotopes in cultural heritage: present and future possibilities’ Heritage Science 6, 25 (2018). https://doi.org/10.1186/s40494-018-0192-3.
• Catriona J. McKenzie & Eileen M. Murphy, Life and death in medieval Gaelic Ireland, the skeletons from Ballyhanna, Co. Donegal (Dublin, Four Courts Press, 2018).
• M.G.L. Baillie, ‘Seven thousand years of alternative history: the tree-ring story’ Irish Forestry 56 (1999), pp 29-38. https://journal.societyofirishforesters.ie/index.php/forestry/article/view/9881. 13 June 2021.
• Byrne RP, Martiniano R, Cassidy LM, Carrigan M, Hellenthal G, et al. (2018) ‘Insular Celtic population structure and genomic footprints of migration’. PLOS Genetics 14(1): e1007152. https://doi.org/10.1371/journal.pgen.1007152.