The discipline of Human Osteoarchaeology has been an integral component of the study of people – their lives, health, and behaviours – for many years. Having recently grown in popularity, the field has expanded to include palaeodemography, palaeopathology, and many other subdisciplines. Not only this, but osteoarchaeology has been incredibly informative to clinical studies – bettering our understanding of disease, ageing, and behavioural changes to modern humans. This field seems, on the surface, to be a positive cornucopia of information, the holy grail to understanding past populations as well as living ones.
One of the major factors that confounds this field is that of the osteological paradox, examined in detail by James W. Wood in 1992. A major component of his theory is that humans who suffer from acute, lethal forms of disease typically do not live long enough for the infection to reach the bone and produce skeletal changes. Patients are therefore not diagnosed with any conditions during osteological examination. Those who developed chronic illnesses, showed resistance, or were able to successfully manage the disease for many years would show bone changes that lead to diagnosis. As such, osteologists are not able to identify the very worst forms of disease – those that would have been immediately lethal to the sufferer. Therefore, the prevalence of disease that is visualised in skeletal remains vastly underestimates the number of individuals who may have actually suffered from disease.
Most conditions that adversely affect the health of a person do not manifest in the skeleton until it has ravaged the soft tissues, cartilage, and ligaments. Modification to the skeleton is often the very last symptom of a disease, infection, or degeneration, making those who are the most susceptible, and often the most crucial to study, completely invisible in the archaeological record. These individuals, who succumbed to their condition far before skeletal changes could occur, can appear to be in good health at the time of death. Combatting this osteological paradox is challenging and at many times incredibly frustrating. There is no true way to get around the paradox, and so research has now turned toward accounting for the limited knowledge that can be gleaned from the study of human remains.
A new hope rises in the form of biomolecular analysis, however. Extensive databases containing information about pathogenetic DNA and ancient DNA are now employed to test for specific conditions within ancient human skeletons using Polymerase Chain Reaction (PCR) testing. This breakthrough, which has soared in popularity in recent years, may provide a more accurate method of assessing pathological disease, finally accounting for those individuals who contracted an illness but did not show skeletal changes before death. This method has been tested on a collection from St. Peter’s Cemetery, Blackburn, where the mid-19th century skeletal sample was supplemented by historical medical records that detailed the suggested cause of death. In this collection, 25% of individuals were recorded as suffering from Tuberculosis, although osteological investigation revealed that only 0.9% of the 1,967 individuals possessed lesions attributable to the disease. PCR testing was employed on a sample of 100 individuals from the site, targeting ancient M. Tuberculosis DNA. The results yielded 25 individuals who had been infected with Tuberculosis or Brucellosis, a closely related disease with similar symptoms, at the time of death. In this way, the biomolecular analysis correctly identified the proportion of the population who had suffered from the disease.
As with most good things, however, biomolecular analysis does not come without complications. The most accurate method of conducting this analysis is to sample directly from a skeletal lesion suspected to be caused by a certain condition. The pathogen can then be tested for a positive match. Often, when the individual has shown no signs of poor health, bone must be sampled from a location most likely to contain the aDNA that is the object of study. Often, this is cortical bone from a dense bone such as the femur. If the disease did not spread to this area of the body, it may go undiagnosed even if PCR testing is employed. The other complication of biomolecular analysis is that it is very targeted – PCR sequencing is typically able to test a short strand of DNA at a time, meaning that researchers must have an idea of what the person was suffering from before conducting tests. It is simply too expensive and time consuming to test an individual for every known pathogen, especially when the sample collection is quite large, and results may yield no viable information. Finally, some diseases which are caused by a more general pathogen, such as Syphilis, are not distinguishable from their biological relatives through aDNA study. Particularly when assessing ancient forms of disease, the genome of the modern, clinical comparison may have been altered between the time of infection and the collection of a modern sample to populate the DNA database.
It seems, then, that biomolecular analysis does not provide the straightforward and infallible solution to the paradox that researchers had hoped. This does not mean that aDNA analysis should be abandoned with regard to pathological investigation – but that it will not replace osteological analysis in the near future because of its many complications. The most logical conclusion at this time is to employ biomolecular study (aDNA, isotope analysis, etc.) in tandem with osteological investigation in order to identify and isolate those individuals most likely to have suffered from disease, or to identify those diseases most likely to have affected a specific community. In this way, biomolecular analysis can be more targeted and have a higher chance of yielding results. It has often been said that archaeologists and biomolecular scientists are uneasy bedfellows; it is rare that either fully understands the discipline of the other, and so disagreement and enmity is rife between the two groups. This is the time, however, to put aside differences and collaborate in order to create a fuller and more accurate image of our past societies – and to further help those who suffer from similar conditions today.
Written by Etta Coleman
Cohen, Mark Nathan, James W. Wood, and George R. Milner. “The Osteological Paradox Reconsidered.” Current Anthropology 35, no. 5 (1994): 629–37. http://www.jstor.org/stable/2744088.
Matthew Ginnever, Catriona Pickard, Ben Pickard. 2017. Nineteenth-century burials from a Lancashire cotton town: Excavation at St Peter’s Church and burial ground, Blackburn, Lancashire. (Blackburn, UK).