Cross-over electrophoresis is an immunological method, principally used by Margaret Newman, University of Calgary, to identify blood proteins in residues on stone tools. Orin Shanks and colleagues applied this method to the analysis of artifacts from the Late Holocene Bugas-Holding (open) site in
Wyoming, USA. The large area excavation of the site investigated site-patterning of specific domestic activities. Site-specific information was pooled to provide an interpretative framework for the study of possible protein residues and included site formation processes, palaeoenvironmental data, and excavation strategies involved in the recovery of artifacts. Furthermore, considerable testing of reagents, experimental controls, and systematic re-testing of samples were undertaken to reduce the probability of falsepositive results. The results confirmed the processing of faunal species (bovine and sheep) that had been identified in the faunal assemblages. Interestingly, the analyses raised further questions about animal exploitation, with bear proteins also found on three of the seven artifacts returning positive reactions. Bear was represented at the site by only a single skeletal element. Furthermore, the nature of the subsistence tasks identified by the integrated functional approach has provided insights into tool use and re-use. Importantly for blood residue studies, these results support a relatively long-term survival of blood residues on stone artifacts and the potential of identifying species-specific proteins by methods other than DNA analyses, while reinforcing the need for a systematic and rigorous approach to the analysis of purported blood residues in archaeological contexts.
Noreen Tuross and Tom Dillehay undertook an analysis of residues from the site of Monte Verde in Southern Chile. Monte Verde is an open site, with occupation traces contained within a wetland environment on the margin of an ancient tributary of the Maullin River. Two cultural layers were identified at the site: the youngest dated to 13.2-12.5 kyrBP and a second less well-defined unit located some distance from the other site and dated to c. 33 kyr BP. The investigations included a combination of immunological and geochemical approaches to the identification of residues on flaked stone artifacts recovered from both horizons. Consideration of the archaeological and stratigraphic contexts as well as the geochemical characterization of the sedimentary matrix was an essential part of the investigative approach to this study. An analysis of the sediments and site formation processes indicated that the younger cultural layer represented a single occupation event, following which material was rapidly buried and maintained in a consistently anoxic, reducing environment, promoting organic preservation. The geochemical analyses demonstrated the absence of organic matter and the presence of desiccant silica gel in the deposits immediately below the younger occupational layer, and identified a lack of humic acids in the overlying strata suggestive of low microbial activity. Further macroscopic, microscopic, and molecular evidence of the high degree of preservation of organic remains within the cultural strata, in addition to the consistently low temperature of the sediments, indicated that the burial conditions were likely to promote long-term preservation of molecular residues.
Seven artifacts from the two horizons were tested for the presence of residues: three from the 13.2-12.5-kyr-BP habitation level and four from the older (possible) cultural layer. The authors noted that no correlation existed between observed ‘stains’ on the surface of the artifacts and the results of immunological tests for blood residue. One artifact (from the c. 33 0-kyr-BP layer) yielded positive results for the presence of blood protein. For the immunological assay experimental controls, including soil samples and blanks were included. These controls enabled a greater degree of confidence in the interpretation of the results from testing the extracted residues. The ELISA method was used to detect the presence of haemoglobin. A Western blot assay was subsequently used to determine the preservation and source (i. e., species) of the purported haemoglobin-containing residue. The results of this study suggest that it is possible for degraded but detectable components of blood to survive over archaeological timescales, and in sufficient quantities and preservation to be detected using existing biochemical techniques.
The case studies presented above demonstrate how important a rigorous, multidisciplinary approach is for investigating questions of artifact function and use. Not every analysis will necessarily require taxonomic identification. The detection of blood proteins alone may be a useful result, depending on the research question at hand. When approaching the biochemical testing stage, a hierarchical approach should be observed, with the assessment of the nature of the residues as the first step. Identification of residues to species level remains contentious and problematic, and may not be possible. The most fruitful studies will include a survey of all tool-use indicators, including usewear and technological studies, and will incorporate the expertise of both archaeological and biochemical researchers to ensure the effective execution of the analyses and the interpretation of the experimental results.
World History
