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aRNA: A Helpful Friend In Palaeopathology?

20 Dec

It is another quick post from me highlighting another researcher’s work but it is one well worth reading!  Over at So Much Science, So Little Time researcher Dr Kristin Harper has highlighted an intriguing possibility on the direction for the future of palaeopathology.

What is aRNA?

Harper’s post highlights the possible value of aRNA ( ancient Ribonucleic acid) in the investigation of viruses (think influenza and coronaviruses such as SARS) in past human populations in her post on the ability of researchers being able to obtain aRNA samples from 700 year old maize samples.  RNA performs a variety of important functions in the coding, decoding, regulation and expression of genes; essentially RNA acts as the messenger which carries instructions from DNA (Deoxyribonucleic Acid) for controlling the synthesis of proteins in living cells.  DNA itself is the molecule that encodes the genetic instructions that are used in the development and functioning of all known living organisms (including many viruses) however, unlike DNA, RNA is composed of shorter single strands of nucleic acids.  This has made it particularly vulnerable to degradation in archaeological contexts.

The best place to search for evidence of aRNA strands in the human skeleton in an archaeological context would be in the dental pulp cavity, specially the molar teeth.  This seems to be the place where diagenesis  has the least effect on the human skeleton due to both the tough enamel coating found in human teeth and the tooth sockets themselves being fairly protected inside the mandible and maxilla, which is where cortical bone is often dense due to the biomechanics of mastication (Larsen 1997).

I should point out here that the area of genetics is not my specialty but it is an area of inherent interest for me, especially in its applications to palaeoanthropology and palaeopathology.

Why Could This Be Important?

The foundations of palaeopathology are built on the observed changes in human skeletal material and palaeopathology itself often specifically focuses on markers of stress or trauma that can be found in the macro or micro skeletal anatomy.  As a consequence of this many diseases (and indeed traumas) are ‘invisible’ in the archaeological record as they leave no marker of note on the skeleton itself.  The diseases and syndromes that do leave a lesion (which can include blastic and/or lytic lesions) are often said to leave pathognomonic lesions that are, at a basic level, an indicator of the disease or infection processes behind the bone change.

So, as you can imagine, quite often in human osteology we have a ‘healthy’ skeleton of an individual that has died at such and such an age but with no obvious cause of death.  In essence we have the osteological paradox, where those who do contract a disease and die shortly afterwards leave no evidence of bone lesions (or trace of the cause of death) in comparison to individuals who do have severe pathological bone changes but have evidently lived long enough for the disease itself to alter the skeletal architecture; it is, in short, the question of discerning the health of a past population (Larsen 1997: 336).  This is a simplified version of the osteological paradox, a discussion outlining the paradox and it’s full implications and discussion points can be found in Woods et al.’s (1992) article (available online here).

This can have serious effects on our estimates of disease prevalence in history and prehistory, especially in the cases of viruses as they can often kill quickly and leave no skeletal marker.  However because they are cells that were once alive they do leave behind evidence of traces of aRNA.  So any new methodology of being able to extrapolate aRNA of past infections from human skeletal material is welcome as this could potentially open up new insights into past populations and population dynamics.

Further Information

Bibliography

Larsen, C. 1997. Bioarchaeology: Interpreting Behaviour From The Human Skeleton. Cambridge: Cambridge University Press.

Woods, J. W., Milner, G. R., Harpending, H, C. & Weiss, K. M. 1992. The Osteological Paradox: Problems of Inferring Prehistoric Health from Skeletal Samples. Current Anthropology. 33 (4): 343-370. (Open Access).