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Forensic Pathology

Case 3 - An Overview of Forensic Biological Anthropology

Mark Skinner
Professor, Department of Archaeology
Simon Fraser University
Burnaby, B.C.


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The traditional role of forensic biological anthropologists
With the advent of forensic molecular biology providing the potential for unequivocal personal identification, one can question the role of forensic biological anthropology. Actually, our contribution to forensic science and to understanding the biology of human hard tissues continues undiminished.

Forensic anthropologists, at least in North America, are trained in anthropology programs which still emphasize human biology, in its broad sense of human physical variation in space and time, as well as archaeology with an explicit concentration on human material culture and site formation processes. These perspectives form an excellent foundation for further training and experience with a forensic focus. Moreover, the historic academic pillars of socio-cultural and linguistic anthropology furnish the traditionally trained forensic anthropologist with a useful perspective for participation in forensic anthropology in foreign locales.

There are several excellent textbooks which teach detailed human osteology (e.g., White 2000) as well as juvenile osteology (e.g., Scheuer and Black 2000). Recent books which emphasize forensic osteology describe the contribution that we can make to human remains identification (e.g., Byers 2002) as well as the determination of circumstances around death (Reichs 1998). Compilations of enthralling case histories can be found in Maples (1994), Fairgrieve (1999) and Steadman (2003). The significance of natural and unnatural processes that diminish or alter evidentiary quality over time, a field of scientific enquiry termed taphonomy, is treated in important works by Haglund and Sorg (1997, 2002). Finally, the emerging role of archaeology, particularly in the realm of mass graves and human rights, is receiving considerable attention (e.g., Sterenberg and Cox nd). It may not be adequately appreciated that most archaeologists are experts in the assessment of landscapes including botanical evidence (e.g., tree ring analysis) and the recognition, collection, and curation of material culture (e.g., perishable substances like cloth, leather and paper). Thus forensic evidence is conceptually congenial to most archaeologists (Hunter et al. 1996).

Despite these positive features, it is fair to observe that the training of forensic anthropologists is very uneven. Most skeletal biologists who provide forensic expertise have specialties, usually forming the basis of their graduate studies, which are not generally shared. For example, not all forensic anthropologists are capable archaeologists; many have no knowledge of botanical and entomological evidence, nor experience with cremated remains, gunshot wounds or facial reproduction, for example. Thus, pathologists may have to ally themselves with several biological anthropologists to obtain the necessary breadth of forensic expertise. However, most of us are experts in altered states of bone (and teeth); a knowledge area that is not duplicated in other medical and forensic disciplines. Forensic biological anthropologists can contribute significantly to the tasks of evidence recovery from crime scenes, determination of elapsed time since death as well as circumstances around the time of death. Finally, we can reconstruct a lot about a person’s life before they died to assist in the task of identification.

Our role in evidence recovery from crime scenes
What are archaeologists doing at crime scenes? Simply, we are experienced in mapping objects within sites and using such observations to reconstruct behaviors that created the site. Central to our expertise is an understanding of site formation processes. Typically, in domestic situations, sites are fresh and have had little opportunity to change. Sites that contain skeletonized remains are usually months or years old before they are investigated. Also, the decay and scattering of remains in such sites have often had a large and disseminated impact on the scene and its environs. Sites change over time. Only archaeologists have an understanding of site transformation processes on this scale. Perhaps the single most important event in forensic anthropology in the past ten years was the release of satellite photographs by US Ambassador to the UN, Madeleine Albright, in 1995 showing areas of disturbed ground at many locations in the former Yugoslavia thought to be mass graves of individuals murdered in the conflicts which raged from 1992 onwards. The Serbian authority’s response was to rob these graves and bury the commingled, decomposed remains in numerous clandestine secondary graves. The detection, excavation and recovery of a mountain of physical evidence including thousands of bodies, fell to a select group of archaeologists and scenes of crime officers (SOCO’s). From this experience has emerged an increasingly sophisticated discipline of forensic archaeology (Skinner et al. 2003).

A myriad of major factors (e.g., carnivores and rodents) and minor factors (e.g., root acids) seriously affect bones. The essential role of the forensic taphonomist is to distinguish natural postmortem processes from unnatural perimortem processes in a rigorous exercise of differential diagnosis. In this way the pathologist may be prevented from overdiagnosing damage to remains.

The sine qua non of archaeological method is the recording of spatial relationships based on the fundamental principle that usually the older stuff tends to be at the bottom of a deposit. Experience with this principle enables the archaeologist to recognize and record site disturbances, both natural (e.g., rodent action, slumpage) and unnatural (re-visits by a perpetrator). It is important to distinguish between simple two-dimensional mapping, typically using a grid system, familiar to many evidence officers who deal with, for example, motor vehicle accidents and plane crashes versus three-dimensional mapping which is essential for the archaeological reconstruction of spatio-temporal relationships in buried remains. Another key concept in archaeology is “association”. In a forensic context, the relationship among objects including deposits, is central to documenting the significance of abnormal anatomical relationships due to disarticulation from dismemberment (e.g., CH-East Timor) as well as decompositional movement producing dissociation of skeletal elements (e.g., secondary mass grave sites). An interesting example of association is afforded by the abnormal occurrence of a mass of fly pupae inside a cranium due to its having been breached by a fatal blunt impact (case history (CH) to be presented).

The primary skill of the anthropologist is in recognizing and interpreting varying and altered states of bone. Such alteration occurred both during the individual’s lifetime (e.g., innate traits of ancestry, sex and stature; as well as acquired features such as robusticity or healed fractures); around the time of death (e.g., gunshot wounds and cut marks); and, subsequently, due to various influences such as cremation, (re)burial, decomposition, scavenging and weathering.

The method of killing and subsequent treatment of the dead by a perpetrator are very important in determining circumstances surrounding death and to the ultimate determination of the cause and manner of death. While legally and historically, the latter judgments are the province of the pathologist and medical examiner/coroner, both the archaeologist and anthropologist often encounter evidence germane to this question. The archaeologist is able to distinguish among the following site types: execution site, surface disposal, primary grave, secondary grave, disturbed and looted grave, cremations and so on (Jessee 2003). Cavalier and disrespectful disposal of bodies can be recorded archaeologically as can the presence of ballistics. Dislocation of the neck due to unskillful hanging in East Timor created evidence that could only be recorded at the time of excavation (CH). Conceivably one could try to preserve this abnormal anatomical relationship until the body could be examined by a pathologist back in the morgue, as is done in the case of ligatures by wrapping the forearms and hands in Saran Wrap around the wrists-a novel, if routine, practice during the exhumation of Srebrenica victims by teams fielded by the International Criminal Tribunal for the former Yugoslavia. In one homicide case here in British Columbia, the police investigators encountered head hair distributed throughout the grave fill; an oddity explained by the absence of the head which the perpetrator had removed at a second excavation weeks after decomposition had started.

Archaeologists are familiar with keeping records of artifacts and so the creation of evidence catalogs designed expressly for the purposes of maintaining a chain of custody, comes easily. Similarly, archaeologists are trained in the recognition of botanical evidence that may bear upon the determination of seasonality and elapsed time since death. Many have taken instruction in pollen analysis and dendrochronology. An interesting application of the latter knowledge occurred in Serbia where transport of bodies in large trucks down narrow wooded paths broke branches leaving a permanent record of its timing as the trees healed their wounds.

Our role in identification
The first determination expected of the anthropologist is whether the bones are human or not. The human skeleton is unique compared to other mammals by virtue of its adaptiveness for bipedal locomotion combined with an enormously enlarged cranium coupled with a tiny dentition. Even small fragments of the face, skull and postcranial skeleton bespeak these differences. Another unique human attribute is our delayed maturation such that it takes us three or four times longer to grow up and ultimately die than it should for our body size. The important forensic consequence of this physiological difference is that at the histological level our bones are dominated by highly remodeled haversian bone. So it is usually quite easy for an anatomist to recognize human bones, even in small pieces, unequivocally.

The core expertise of the human osteologist is to provide opinions as to ancestry, sex, stature and age at death. While each of these remains an area of active research, as can be attested by any issue of the forensic science journals, here I will emphasize only new advances or important perspectives that the non-specialist should have on the anthropologist’s contribution.

The whole concept of ancestry determination in forensic anthropology has been severely critiqued in recent years (e.g., Goodman 1995). There is frank recognition that while society recognizes bounded categories (Black, White, Whatever), human beings belong to unbounded genetic clusters which grade more or less imperceptibly into another with only the extremes being visibly different. Consequently, biological attribution may bear little resemblance to social categorization. Complicating this picture is the recent widespread mixing of populations drawn from all over the world. Investigative methods for the anthropologist include morphological analysis, osteometrics and minor anatomical variants of the skull and dentition. The interested pathologist can read the methods in Gill and Rhine 1990, Turner et al. 1991).

Sex attribution from just bones, including those of children, has been revolutionized by recognition of the amelogenin gene (Slavkin 1997). Except in rare cases of the complete absence of cellular structure (e.g., cremations), this is the preferred method. Of interest, however, are those not infrequent cases in which cellular sex does not match with skeletal markers especially of the face. In the author’s personal experience, undeniably female individuals had skeletons which looked rather masculine (biker gang case, sex trade worker). One wonders why.

I suspect that stature determination from limb bone length is largely a waste of time. We know that, approximately 80% of missing persons have statures falling within two standard errors of the predicted value (Skinner 1988); so unless the bone is from an extraordinarily short or tall person, estimating stature is not individualizing at all. With that said, osteometry of the limb bones continues to be forensically useful in cases of limb asymmetry (e.g., in brachial plexus nerve damage at birth, or nerve damage due to limb fracture in childhood).

Determination of age at death is the thing anthropologists do best (although not very well). It is our most active area of research because of our wish to reconstruct accurately the demographics of ancient skeletal populations. Most of our age markers have correlations with real age of 0.8 or worse which really means we can only slot the missing person into one of two categories (young vs. old adult). Two observations give me hope. Firstly, when one has multiple age indicators (e.g., medial clavicle, pubic symphysis, auricular surface, vertebral centrum surface, root translucency, joint lipping, tooth loss), the age at death estimates (usually given as a 10 year range) almost always have been shown to include the actual age (personal experience working with Srebrenica individuals). Secondly, recent work strongly suggests that cementum increments on tooth roots are indeed annual (Wittfer-Backhofen et al. on line) with a correlation between predicted and actual age of 0.97. This is very encouraging.

Forensic cases form a mortality cohort which differs biologically (and socially) from the general population; for unexplored reasons, they tend to have been socially and nutritionally marginalized from early on in life such that their developmental environment is less than optimum. Thus it is important for the death investigator to keep in mind that in forensic work one will encounter negative skeletal and dental conditions more commonly. Thus, we have observed osteopenia of facial bones in children drawn from recent immigrant populations to Canada (the marker of this is localized hypoplasia of the primary canine tooth) (Skinner et al. 1994), markedly pinched or cleft palates (CH-SS case), dental crowding, as well as lines of disturbed growth in the enamel (CH-Skinner and Anderson 1991) and frank enamel hypoplasia (CH-SC). Distinctively negative hard tissue sequelae may help identify someone or may provide evidence of chronic child abuse or neglect prior to death of a child.

Our role in determining elapsed time since death
Few forensic anthropologists feel comfortable with estimating elapsed time since death from decompositional changes, except crudely and rather uselessly. But the forensic archaeologist can play a very useful role in recognizing and recovering botanical evidence including severed tree roots, for example, or pollen which can show seasonality or exotic origin. We have learned in Canada to defer to the essential expertise of the forensic entomologist in deaths less than a year or two old.

Our role in determination of manner and cause of death
Most osteologists are entirely comfortable with the recognition of postmortem damage to bones; so-called taphonomic changes. Typically, this is due to animal chewing and gnawing (CH-Stanley Park case). More problematic is the recognition of antemortem bone changes that occurred a few weeks or months before death(CH-Knox Mountain) and distinguishing these subtly remodeled bone changes from unremodeled perimortem events. The impact of perimortem trauma on bones is an active research area in human skeletal biology; so pathologists could draw useful expertise from this quarter. For example, crack intersections forming a “T” permit the sequencing of blunt impacts to a skull (CH). The complexities of disintegrating joint integrity in the upper cervical region can be revealed by examination of repeated machete blows to the neck (CH). Bone is a remarkably useful medium for recording faint striations that can be linked back to the cutting edges of particular axes (CH). One of our students has recently undertaken a study of oral gunshot wounds to determine if bilateral fracture of mandibular coronoid processes could be also produced by carnivore chewing. The answer is ‘no’ (Puskas 2003). Interestingly, a British pathologist colleague has observed that American anthropologists have more experience with GSW’s than do British pathologists. In another case from East Timor the investigators mistakenly at first diagnosed a protruding piece of metal in the wrist as an electrode from some kind of torture apparatus when in actuality it was a defense wound from clipped nail shot in a homemade shotgun (CH).

Problematic areas
It is important to create and maintain a functional link between anthropologists and forensic pathologists. In my experience this has not been easy. The bridge between these two intellectual communities is often the medical examiner’s office whose staff changes frequently and communications are lost. Also, it seems pathologists change posts remarkably often, while tenured anthropologists tend to be restrained by golden handcuffs.

Forensic anthropologists are experts in bone; but we have to be able to see it. I am curious how often forensic pathologists decide not to engage an anthropologist in examination of remains simply because of the time it would take (a few days) to render the flesh from the bones. We have found that the use of instant, two-component spray glues will allow complete reconstruction of a multiply shattered cranium in less than an hour; greatly enabling the pathologist’s reconstruction of entrance, exit and number of GSW’s.

We have found in mass grave work that the responsibility for examination of the dentition and any dental work is relegated all too often to the more or less reluctant pathologist and, typically, the ultra-keen ingenue anthropologist who can hardly wait to get at the teeth. Even though many pathologists and anthropologists have considerable experience with the mouth and the teeth, we believe that this aspect of forensic science, particularly as it occurs in an international context, is sufficiently complex and important that only richly experienced forensic odontology specialists augmented with local knowledge are equipped to meet the challenge (Skinner and Alempijevic 2003).

Another area in which we feel anthropologists fail to recognize evidence in skeletonized remains is bone marrow that may contain drug or chemical residues. Many such substances can be found in bone marrow months or even years after death (Raikos et al. 2001) and significantly bone marrow is second only to blood as a proxy tissue to determine toxicity. This area needs further research.

References

  1. Byers SN. 2002. In Introduction to Forensic Anthropology. Boston: Allyn and Bacon.
  2. Fairgrieve SI. 1999. Forensic Osteological Analysis. Springfield: Thomas.
  3. Byers SN. 2002. In Introduction to Forensic Anthropology. Boston: Allyn and Bacon.
  4. Fairgrieve SI. 1999. Forensic Osteological Analysis. Springfield: Thomas.
  5. Gill GW, Rhine S. 1990. Skeletal Attribution of Race. Alburquerque:Maxwell Museum of Anthropology.
  6. Goodman AH 1995 The problematics of “race” in contemporary biological anthropology. In Biological Anthropology: The State of Science, edited by Boaz NT, Wolfe LD. International Institute for Human Evolutionary Research, Bend, pp. 215-39.
  7. Haglund WD, Sorg MH. 1997. Forensic Taphonomy. Boca Raton: CRC Press.
  8. Haglund WD, Sorg MH. 2002. Advances in Forensic Taphonomy. Boca Raton: CRC Press.
  9. Hunter J, Roberts C, Martin A. 1996. Studies in Crime: An Introduction to Forensic Archaeology. London: Batsford.
  10. Jessee E. 2003. Some Recommendations for the Creation of a Series of Experimental Mass Graves and Mass Grave-Related Test Sites. Master’s Thesis. Simon Fraser University.
  11. Slavkin HC. 1997. Sex, enamel and forensic dentistry. JADA 128: 1021-5.
  12. Sterenberg J. M Cox M. Forensic Archaeology and the Investigation of Mass Graves. London: Taylor and Francis (forthcoming)
  13. Maples WR, Browning M. 1994. Dead Men do Tell Tales. NY: Doubleday.
  14. Puskas C. 2003. Bilateral fractures of the coronoid processes: Differential diagnosis of intra-oral gunshot trauma and scavenging using a sheep crania model. J For Sci 48: 1219-25.
  15. Raikos N, Tsoukali H, Njau SN. 2001. Determination of opiates in postmortem bone and bone marrow. Forensic Science International 123: 140-1.
  16. Reichs KJ. 1998. Forensic Osteology (Second edition). Springfield: Thomas.
  17. Scheuer L and Black S. 2000. Developmental Juvenile Osteology. NY Academic Press.
  18. Skinner MF 1988 Method and theory in deciding identity of skeletonized human remains. Canadian Society of Forensic Science Journal 21:114-34.
  19. Skinner MF, Alempijevic D. 2003. In the Absence of Dental Records, Do We Need Forensic Odontologists at Mass Grave Sites? Dental Anthropology Symposium, Edmonton.
  20. Skinner MF, Alempijevic D, Djuric-Srejic M. 2003. Guidelines for International Forensic Bioarchaeology Monitors of Mass Grave Exhumations. Forensic Sci. Int. 134:79-90.
  21. Skinner MF, Anderson G. 1991. Individualization and enamel histology: Case report in forensic anthropology. Journal of Forensic Science 36: 939-48.
  22. Skinner MF, Hadaway W, Dickie J. 1994. Effects of ethnicity, nutrition and birth month on localized enamel hypoplasia of the primary canine. J. Dent. Child. 61: 109-13.
  23. Steadman DW. 2003. Hard Evidence. Upper Saddle River: Prentice Hall.
  24. Turner CG, Nichol CR, Scott GR. 1991. Scoring procedures for key morphological traits of the permanent dentition. IN Advances in Dental Anthropology, Kelly MA, Larsen CS (eds). NY: Wiley-Liss, pp. 13-31.
  25. White T. 2000. Human Osteology (Second Edition). NY: Academic Press.
  26. Wittwer-Backofen U, Gampe J, Vaupel JW. 2003. Tooth cementum annulation for age estimation: Results from a large known-age validation study. Am J Phys Anthropol (on line).