Forensic Anthropology, Osteology, and Taphonomy
Dave Carlson - September 1, 2006
Haglund and Sorg (1997) offer some definitions to help frame this article:
- Taphonomy is “the study of death assemblages” (p. 1), including “all aspects of the passage of organisms from the biosphere to the lithosphere” (p. 3).
- Forensic anthropology is “the application of methods and theories of physical anthropology and archaeology to the medicolegal investigation of death” (p. 1).
- Osteology is “the branch of anatomy that deals with the structure and function of bones” (www.answers.com/osteology).
Foran (2006) emphasizes that positive identification of unidentified human remains is a significant goal of any forensic examination (p. 12). Antemortem reference records such as fingerprints, clothing, artifacts recovered in close proximity to the remains, unique skeletal features, and dental arrangement all leave clues to a person's identity (Foran, 2006, p. 12). When these records are not available or are inconclusive, the forensic examiner may turn to DNA analysis, which was first introduced in 1989 (Foran, 2006, p. 12).
Human bone persists for an exceedingly long time, but "like any tissue, bone breaks down postmortem, and given enough weathering becomes so fragmented that it may be unidentifiable" (Foran, 2006, p. 13). As bone breaks down and deteriorates, its organic molecules mutate and degrade at various time intervals, depending on environmental conditions. It is known that various soil conditions, such as warm temperatures, high moisture contents, and pH levels accelerate DNA degradation. What is not known, however, is if the physical appearance of bones has any direct correlation with the quality of DNA contained within the bone molecules (Foran, 2006, p. 14).
There are several different types of DNA. The primary mode of DNA typing of aged skeletal remains is Mitochondrial DNA (MtDNA) analysis. A complete sequence of human MtDNA was identified in 1981 (Foran, 2006, p. 14). In his study, Foran (2006) details methods used to extract MtDNA and its use in forensic identification (p. 15).
The objective of Foran's study "was to determine if the visual appearance of skeletal remains can be used as a reliable metric of the DNA (particularly MtDNA) found within, or: Is there a relationship between the level of bone weathering and the quantity and/or quality of DNA that may be used for analysis?" (Foran, 2006, p, 15). Even though scientists had been extracting DNA from bone for years, no one had established a direct correlation between the appearance of a bone and its potential to yield viable DNA for analysis.
The study began with these assumptions: (1) different bone types (long bone, flat bone, teeth, etc.) might yield different results, (2) other factors, such as soil conditions, “might affect bone diagenesis” (Foran, 2006, p, 16), and (3) methods existed to enhance "the acquisition of DNA data from aged skeletal remains" (Foran, 2006, p, 16). It was important for the study to have access to a large sample size of bone samples from known environmental conditions. Foran teamed with Dr. Doug Ubelaker, of the Smithsonian Institution, who arranged for skeletal material from a burial site, referred to as the Voegtly Cemetery (Foran, 2006, p. 16).
Foran (2006) describes in detail the history of the cemetery and the archeological methods employed to excavate the remains. The site was treated as an archeological dig and all recovered materials were painstakingly identified and preserved. “All skeletal material was wrapped in aluminum foil, placed in plastic bags, and labeled” (p. 18). The dig recovered the remains of 724 individuals, a more than adequate sample for the study.
After disinterment, the remains were transported to the Smithsonian Institution for detailed identification and cataloging. Smithsonian scientists were careful to assess and log "the overall condition (degree of weathering) of each skeleton" (Foran, 2006, p. 20). The scientists used a well-known archeological scale of 0 - 5 to classify the bones.
- Stage 0 -- A bone sample whose surface shows no sign of cracking or flaking due to weathering;
- Stage 1 -- Bone shows some cracking, usually longitudinally in long bones;
- Stage 2 -- Cracks and some flaking of bone;
- Stage 3 -- Bone surface has rough patches of weathered compact bone down to 1.5 mm, with extensive flaking although bone fibers are still attached to each other;
- Stage 4 -- Bone surface is course, splinters may exist and fall out, and weathering reaches the interior portions;
- Stage 5 -- Bone is easily broken and is disintegrating. Original shape may be hard to determine. (Foran, 2006, p. 20)
The vast majority of the bones in the Voegtly Cemetery collection were classified within stages 2 - 5, with a few in stage 1. Considering the bones had been buried for more than 150 years, it is not surprising that no meaningful number of samples were identified in stage 0 (no signs of weathering) (Foran, 2006, p. 21). Criteria to determine MtDNA quality of samples:
The degree to which DNA is degraded in a sample dictates the size of DNA fragments that can be amplified, and thus the level of genetic information that can be retrieved. If a sample is too far degraded the remaining small fragments of DNA are of no use for identification. In contrast, a sample retaining high molecular weight DNA, regardless of age, can yield a wealth of data. (Foran, 2006, p. 23)
Foran’s study detailed the specific methods utilized to retrieve and isolate DNA from each sample tested. The study specifically analyzed a subset of 89 bones (Foran, 2006, p. 29). “A total of 2 crania, 28 femora, 1 fibula, 25 pelves, and 33 ribs were tested, coming from a total of 36 individuals.” (Foran, 2006, p. 30). These bones spanned a classification range of 1-5.
Foran (2006) concluded that there was no scientific correlation between bone exterior appearance and the ability to extract viable DNA (p. 92). However, he did establish that “long bone, teeth, and petrous portions, and to a lesser extent ribs, make good targets, while spongy bone does not” (p. 92).
Foran, D. (2006). Increasing the predictability and success rate of skeletal evidence typing: Using characterisitcs of bone as a metric for DNA quality and quantity. [Electronic version]. Unpublished research report submitted to the U.S. Department of Justice.
Haglund, W. D. and Sorg, M. H. (Eds.) (1997). Forensic taphonomy: The postmortem fate of human remains. Boca Raton, FL: CRC Press.