If you watch the tv show Bones, you know that every once in a while Brennan will determine some activity that the deceased did based purely on their skeletal remains. For example, in the Pilot episode she determines that the deceased is a young woman who played tennis. The determination of the activity was based on the presence of specific robust muscular attachments in one of the arms. In another case, Brennan determined that the individual was a musician based on the strong fingers, and yet another example was the strong muscular markers in the bones of a chicken to determine it was free range. While these are very helpful in the TV show for immediately narrowing down identification of the deceased, this is not how is type of identification works in real life. First, let’s discuss musculoskeletal stress markers or entheseal changes.
Depiction of Entheses, via Wikimedia
The body is made up of three types of muscles: two are used for organs and transport of fluids, and the other is the skeletal muscles that connect to our bones and allow movement. Each of these skeletal muscles has multiple attachment sites known as the origin, point of attachment to a stationary bone, and insertion, point of attachment to a moving bone. These are also called entheses. Ligaments, tendons and cartilage form similar attachments as well. As these muscles, tendones, ligaments and cartilage are used and stressed, they form stronger attachments to the bone. Therefore, long term repetitive activities will cause certain attachment sites to become more pronounced. In human remains, these sites of attachment are known as musculoskeletal stress markers, occupational markers, or entheseal changes, and can be used to interpret activity in the past. They have been used in a wide variety of ways to interpret activity in dead populations, including variation in activity between different genders, change in activities with agriculture, determining social status based on activity, and has also been used more specifically to interpret occupation such as the gladiator site in York where different forms of fighting were determined, or the Mary Rose warship remains who were divided on occupation within the ship.
The newest issue of the Internal Journal of Osteoarchaeology is dedicated to this topic of entheseal changes, examining new technical and theoretical approaches, various case studies, and applications of this type of research. While we understand that muscles do have an effect on the bone- it is not completely clear why certain sites become more pronounced than others, and whether this process is standard in every human. There is also no one to one correlation between a muscular mark and an occupation. Unlike Bones, we can only determine that the site was stressed- not what the exact activity was that caused it. Other problems include the fact that different sites are stressed in different ways, for example there are different changes in sites that a purely muscular and ones that are cartilaginous. Further, these markers are very sensitive to age, and it was found that this was the most common cause of differences- older individuals create more stress and change to the entheses. Certain bone forming diseases can also lead to changes and may bias interpretation (Villotte and Knusel 2013). Understanding why the bone changes at these sites requires knowledge of what attaches there, how it is affected by change, and also knowledge of the individual’s age, sex, health and ethnicity.
A) notable change to entheses on ulna with large exostosis at top B) ulna with less entheseal change and no exostosis, via Henderson et al. 2013
The best way to learn about the relationship between occupation, individual, and these entheseal changes is to examine known collections. Cardoso and Henderson (2013) examine a skeletal population from Portugal where occupation is known in order to determine the correlation. The sample consisted of 211 individuals from two collections where information was known about the individuals. Only males were used because most females had the same occupation recorded, and therefore wouldn’t be helpful to the study. They were divided into five categories with different levels of stress (non-manual, light manual and hard manual): commerce/transport, farmers/servants, government/services, skilled workers/artisans, or unskilled worker. They found that entheseal changes did vary based on the different occupation types and levels of labor. However, sorting individuals by intensity of labor rather than occupation type was more useful- for example skilled labor included highly manual jobs like stonemasons and low manual jobs like photographers. Like other studies, they found that age was problematic as older individuals have higher rates of changing occupation and entheseal changes.
Another study by Henderson et al. (2013) examined how changes in occupation or occupational mobility, causes increased presence of entheseal changes and degeneration in joints. The study sample includes 18 adults with known occupations from an English cemetery. They recorded robusticity of various entheses, demographic information about the individual (age, sex, health), and compared these against known historical and diary data from the period. They found that recorded occupation for these individuals did not always match the patterns of entheseal changes. For example, tailors had higher prevalence of change on the right side, though one had evidence of high stress on both arms. They argue that this may be due to changing occupations and occupations overlapping with other work. Their research showed that there are patterns in occupation and entheseal changes, but that they aren’t always straightforward and must consider changes in occupation. This study is important because it shows that the whole life, not just final occupation must be taken into account.
While there are problems with interpreting occupation, it is important to our studies that we continue to do so. The variation in skeletal markers can be revealing about age, sex, gender, ethnicity, class and disability- all important factors in interpreting past communities. It is difficult, requires knowledge of the soft tissue, an understanding of change over an individual’s life, and one must know the context the individual lived in- however, the benefits outweigh the challenges. I strongly suggest checking out this whole special issue to learn more about how this type of analysis has drastically improved, and how you can incorporate it into your work.
Works Cited
Villotte, S., & Knüsel, C. (2013). Understanding Entheseal Changes: Definition and Life Course Changes International Journal of Osteoarchaeology, 23 (2), 135-146 DOI: 10.1002/oa.2289
Cardoso, F., & Henderson, C. (2013). The Categorisation of Occupation in Identified Skeletal Collections: A Source of Bias? International Journal of Osteoarchaeology, 23 (2), 186-196 DOI: 10.1002/oa.2285
Henderson, C., Craps, D., Caffell, A., Millard, A., & Gowland, R. (2013). Occupational Mobility in 19th Century Rural England: The Interpretation of Entheseal Changes International Journal of Osteoarchaeology, 23 (2), 197-210 DOI: 10.1002/oa.2286
Bones Don't Lie 