Theory and Methods of Forensic Anthropology

Introduction

Forensic anthropology can be defined as the study of human skeletal remains in the course of a legal inquiry. It is a sub-discipline of physical anthropology- the study of human evolution as it relates to biological variation and race classification, especially skeletal biology (Ball, 2010; James & Nordby, 2003). Physical anthropology stems from Charles Darwin’s theory of evolution, notably that of natural selection. Physical anthropology studies this evolution of man as it relates to biological changes stated by Darwin.

Figure 1 Skeletal remains (St. Thomas University, Department of Anthropology, 2010)The widespread forensic need for expertise in anthropology emerged from the investigation of death and injury for criminal and civil legal inquiries (James & Nordby, 2003). The forensic recovery and examination of human remains cuts across several disciplines and thus involves a team of experts from these disciplines. Often the levels of competencies and expertise cut across the disciplinary boundaries of members of the team (James & Nordby, 2003). According to James and Nordby, although cultural anthropologists are not usually involved in forensic work, forensic anthropologists with expertise in archaeological methods have within the last three decades played prominent roles in recovering human skeletal remains. The forensic anthropologist applies varying scientific methods to examine and obtain extensive measurements from bones in order to give an identity (sex, age, race and stature) to the unidentified skeletal remains (St. Thomas University, 2010). Further analysis may reveal the state of the health of the decedent(s), if they were right or left-handed, if they had a child, and sometimes their occupation could be determined (Nafte, 2000).

Forensic anthropology applies not just in criminal cases in the U.S and England but also in Yugoslavia, Guatemala and Argentina where there have been mass burials, and in concentration camps of World War II (Minnesota State University, 2005-2010). This essay aims to discuss the theory and methods guiding the practice of forensic anthropology. This will be achieved by highlighting the body of knowledge that governs forensic anthropology and by establishing what forensic anthropologists do and how they go about achieving their set objectives.

Theory Governing Forensic Anthropology

Charles Darwin and Anthropology

The theory of forensic anthropology has its roots in Darwin’s theory of evolution. In his “On the Origin of Species” (1859), Charles Darwin postulated that the process of natural selection was one in which some individuals of the same species developed slight anatomical variations from others that gave them the added advantage to compete for scarce resources and hence ensure their survival. This he stated, eventually resulted in the production of new species, with many species sometimes evolving from one ancestry (Reeder, 1997). Furthermore in his “The Decent of Man” (1871), Darwin used the concept of primate evolution to explain human traits, suggesting the process of adaptation as responsible for variable human traits like skin colour (Weiss, 2009). According to Weiss, Darwin developed the theory of sexual selection as an explanation for their evolution. In another book “Expression of the Emotions in Man and Animals” (1972), Darwin used data from different interactive cultures to explain behaviour that were common to humans around the world in order to show that the human species evolved from a single ancestry (Weiss, 2009).

Figure 2 Charles Darwin (Photograph by Leonard Darwin, 1874)According to Weiss (2009), in these ways Darwin was a good anthropologist who was able to distinguish between cultural and biological evolution. This influenced the evolution of the study of anthropology which is the study of human beings – where they come from, their various ways of living in different societies world-wide, and their interaction with their environment. Thus anthropologists may be considered to be Darwinians (Weiss, 2009). The distinction between cultural and biological evolution defines the two main groups of anthropology – cultural anthropology and physical anthropology. Physical anthropology provides explanation from evolution theory about patterns of human shape and size, including difference in growth, development, pathology and population. It fundamentally seeks to understand the causes of present diversities in the human species (Discover Anthropology, 2010).

Although physical anthropology encompasses essentially distinct fields such as paleoanthropology (the study of fossilised remains of early primate species), primatology (the study of nonhuman primate societies), epidemiology (the study of diseases), human biology (physical growth, adaptability and change), and osteology (the study of bones), the practical and theoretical understanding of (osteological) human skeletal variation provides the expertise that the forensic anthropologist uses to interpret individual cases and the foundation for forensic anthropology (Nafte, 2000; James and Nordby, 2003).

Methods of Forensic Anthropology

The Work of a Forensic Anthropologist

Skeletal remains have been found in various ways, locations and states. Forensic anthropologists usually get involved after being notified by the law enforcement agents or agency. Often, they work with medical examiners and coroners where the identity of the skeletal remains cannot be determined by other means such as fingerprint, dentition or DNA (France, 2009). They set out to develop a biological profile that identifies the decedent based on sex, age, race and stature and also try to isolate any particular feature that gives better recognition to the unidentified remains (James and Nordby, 2003). Forensic anthropologists may also testify in court as expert witnesses for the prosecution or defence. Their role is to present the results of their assessment of the skeletal remains impartially (Saferstein, 1982; Nafte, 2000; James and Nordby, 2003).

Forensic anthropologists also examine flesh, fragmented body parts from mass fatality, burnt bodies, decomposed and mummified remains (Nafte, 2000; France, 2009). According to Nafte (2000), forensic anthropologists may also be involved in locating and recovering of remains, interpreting movements before, during and after death, analysing the scene where the remains were found, and in the preservation of materials such as bodily fluids, soft tissue, insects, soil, and clothing for other analysts.

The analytical methods employed by forensic anthropologists when determining the biological identity of decedents entail both direct observations and obtaining extensive measurements. Traits determined by shape and size of the bones are analyzed, recorded, computed and compared to established standards. The aim of the forensic anthropologist is to minimize the range of possible persons to a minimum population. Success therefore demands that the forensic anthropologist is well vast in knowledge of, and also very familiar with the differences in skeleton within and between populations (Nafte, 2000).Thus in order to establish the identity of a decedent, the forensic anthropologist employ various methods to answer the following questions:

Are the Skeletal Remains Human?

To the untrained eyes, human skeletal remains are very often confused with that of animals especially where no skull exists or where human and animal remains are mixed. Difficulties in identification can be further complicated in instances where they have been scattered and damaged. This is the more common scenario as animals usually scavenge on dead remains (Ball, 2010). If all the bones are intact, it is easy to confirm if they are human. In cases where the bones are from human fetal or infants, they are very likely to be undeveloped, small and different in shape from adult bones, thus making distinction difficult from nonhuman animal remains (Nafte, 2000). The forensic anthropologist is trained to determine human skeletal remains by physical inspection. However, if the bones are fragmented but recent and still contain protein, then serological tests for specific species are applied. Mitochondrial DNA tests can also be used (Jackson & Jackson, 2008).

Are the Skeletal Remains of One or More Persons?

After confirmation of its human identity, the forensic anthropologist proceeds to determine the number of persons that make up the skeletal remains. The recovery of human skeletal remains from a possible crime scene is an essential aspect of the involvement of a forensic anthropologist in an investigation. Bones are very carefully and systematically removed and collected from where they are discovered. The operation requires mapping, video recording and/or photography, thorough search of the site around the remains, collecting, packaging and transport of all the evidence associated with the scene (James and Nordby, 2003; Nafte, 2000; Ball, 2010). This is where forensic anthropology gets its tools from archaeology as a lot of the tools and techniques used in excavating and packing human remains (particularly where the remains have been buried or scattered) are those used in archaeology (James and Nordby, 2003; Nafte, 2000; Ball, 2010). The bones from the excavated remains are carefully sorted and catalogued in an inventory. As part of the inventory, any particular bone found is described in detail and listed independently. From this inventory, the number of persons making up the skeletal remains is determined. This inventory also establishes whether there has been a commingling of human and animal skeletons (Winson, 2004).

Is the Decedent a Male or Female?

Next, the sex of the decedent is determined by utilizing sexual dimorphism- the difference between male and female bones (Camp, 2005; France, 2009). According to France, these differences are not usually established until after puberty and this makes identification of very young individuals extremely difficult and unreliable. After puberty, males tend to be larger than females and areas in the bones where muscle attachment take place are larger and more rugged. However, in order to utilise sexual dimorphism the race needs to be known (France, 2009; Winson, 2004). The average skeleton size and degree of sexual dimorphism and proportions differ greatly between populations (Nafte, 2000; France, 2009). For example, the skeletons of native Indian populations are usually smaller and show less sexual dimorphism than Australian Aborigines. Consequently, an adult skeleton of an Asian Indian male placed alongside that of an adult male (or many females) Australian Aborigine would be wrongly classified as female based on size (France, 2009).

To the forensic anthropologist, the most reliable and obvious difference between male and female skeletons can be found by direct observation of the pelvis (Rhine, 1998; France, 2009). This difference is more pronounced in this region because the female pelvis is shaped differently to allow for child bearing (Ball, 2010; France, 2009; Adebisi, 2009). See Figure 3a and Figure 3b below.

Figure 3a Female pelvic girdle (France, 2009)

Figure 3b Male pelvic girdle (France, 2009)The skull or cranium is another useful bone used for the determination of sex by the forensic anthropologist (Rhine, 1998; Adebisi, 2009). Here, methods used are calibration and physical observation. Male chins are usually squarer while female chins tend to come to a point at the middle. Male foreheads tend to slant backwards while those of females are usually more rounded. Also there is a higher prevalence of brow ridges noticed in males than in females (Minnesota State University, 2005-2010; France, 2009; Nafte, 2000). The calibration process involves measurements taken from the skull using spreading and sliding callipers (see figures 4a and 4b below) and inserted into derived formulae. The results are then computed and compared to standards to obtain final determination of sex (Winson, 2004).

Figure 4b Using a sliding calliper (Winson, 2004)

Figure 4a Using a spreading calliper (Winson, 2004)

How Old Was the Decedent at the Time of Death?

During the formative years of an individual, growth and development are regular processes and the way and stages that bones mature follow an observed pattern. Thus under normal circumstances, they are measurable and predictable (Nafte, 2000). Forensic anthropologists use these observations to determine the age of the decent. According to Klepinger (2006), these measurable features include eruption of tooth, length of bone, dental development, as well as appearance and fusion of growth centres. Measurements of these from different populations of living and dead individuals have been catalogued over several years to a data source known as growth standards (Nafte, 2000). According to Nafte, forensic anthropologists apply these standards comparatively when observing the final stage of growth reached by the decent at the time of death. Unknown skeletal remains can thus be assigned an age with a considerable high degree of accuracy.

The general category of the skeleton however determines the specific age determination technique to be used. For a relatively young individual, the most accurate methods of age determination are tooth eruption times and dental formation (Fisher, 2000; France, 2009). However, in evaluating the age of a fully adult skeleton, forensic anthropologists usually observe degenerative features of bones in other parts of the skeleton. These changes provide corroborative evidence of age but are unreliable as injury and diseases may produce such changes (France, 2009). Comparative analysis of cranial sutures (areas that separate bones of the cranium where growth takes place) and epiphyseal fusion (closing of the growth plates at end of long bone and clavicle) in the young adult skeleton were previously extensively used for age determination but this technique has been proven unreliable by further research (France, 2009; Winson, 2004). Other methods include using pubic symphysis analysis and sterna rib analysis (Nafte, 2000).

Figure 5 Degenerative joint changes in tibia at knee (France, 2009)

Figure 6 Cranial Sutures of the Skull (A.D.A.M. 2010)

What was the Decedent’s Race?

Usually, forensic anthropologists are required to provide the racial identity of a decedent. Bones however do not manifest racial specific genes (Nafte, 2000). According to Nafte, the forensic anthropologist must utilize the extent of visible genetic features observed in the skeletal remains. These features are examined, measured and compared to samples of known individuals to enable the determination of a probable ancestry. The traditional classes of race are Caucasoid, Mongoloid and Negroid. However, with more available data coming from research, six geographical races of the world have been classified – Mongoloid, Caucasoid, Negroid, Australoid (Melanesian/Australian), American Indian, and Polynesian (Nafte, 2000).

Very often, the skeletal features of the face, mandible and cranium (craniofacial traits) are first analyzed and measure and then compared to known samples to obtain an approximate race affiliation. This then enables the degree of sexual dimorphism to be better accurately assessed. Next, the nature of the size and shape of the teeth are analyzed, as specific cultural and genetic features may point to certain populations. Finally, the profile of the skull is examined to determine the extent to which the upper and lower jaw project outwards. The information obtained from all of the processes indicates a particular population over the others (Nafte, 2000).

Another method used (discriminant function method) developed by Giles and Eliot (1962) involves imputing into formulae, extensive measurements taken from the skull of the decedent. This is then computed and the score used to ascertain the biological affinity of the decedent (James and Nordby, 2003; Nafte, 2000).

What Was the Decedent’s Stature?

The height of the decedent may be determined by direct measurement in cases where the skeleton is complete. In such cases, the lack of tissue must be taken into account (Fisher, 2000; Jackson & Jackson, 2008). Where the skeleton is incomplete, measurements are taken of one of the long bones (femur or tibia) and the results applied to a set of formulae known as “regression formulae” to determine the stature of the decedent (Fisher, 2000; Winson, 2004; Nafte, 2000). The computed result gives an estimate of the decedent’s height, placed within a range using an osteometric table. Accuracy however is subject to correct interpretation and use of the formulae (Nafte, 2000).

When Did Death Occur?

Medically and legally, interest in bones forensically is limited to recent remains (less than 100 years) as suspects would probably be dead after this time (Jackson & Jackson, 2008). For the forensic anthropologists, estimating the time of death can be very difficult. Unfortunately, radio-carbon dating technique used on archaeological artefacts cannot be applied effectively to bones less than about 100 years old (Jackson & Jackson, 2008). Thus estimating the time of death would depend on the condition of the bones, soft tissue, ligaments present, odor, extent of plant, insect and animal activities as well as environmental conditions (Mann & Ubelaker, 1990).

What Was the Cause and Manner of Death?

According to Ball (2010), the cause of death refers to what caused the person’s death (gunshot wound, blunt force trauma, and/or disease), while manner of death refers to how death may have occurred (accident, murder, suicide, natural or unknown). Forensic anthropologists typically examine bones void of flesh or where the remaining flesh has decomposed beyond the possibility of having an autopsy. This makes it extremely difficult, if not impossible for the forensic anthropologist to determine the cause or manner of death (Nafte, 2000). According to Nafte, the forensic anthropologist primarily comments on the condition of the remains (e.g. intact, burned, fractured, or chewed) and describes the possible types of objects and events that may have resulted in the state in which the remains were found.

Figure 7 Blunt force trauma in cranium (France, 2009)

Figure 8 Gunshot wound in cranium (Forensic Fact, 2008)

Nafte (2000) explains that during analysis of skeletal remains, the forensic anthropologist looks for notable patterns, lesions and identifiable marks on the bone as clues to the nature of trauma, disease, illness or injury. Three periods of time are usually referred to by the forensic anthropologist to distinguish when an injury took place: ante-mortem (before death), peri-mortem (about the time of death), and post-mortem (after death).This establishes the injury’s relevance to the case and its possible association with the individual’s death. Thus the forensic anthropologist may sometimes help in the determination of the cause and manner of death (Nafte, 2000).

Forensic Facial Reconstruction

Figure 9 Reconstructed skull and face of Kennewick man (IUPUI Department of Anthropology, 2010)The human skull holds many clues to the actual appearance of the individual, some of which can be found in the brow ridge, shape of the nasal chamber, distance between the eye orbits, shape and projection of the bones of the nose, the chin’s form, and the general profile of the face bones (Smithsonian National Museum of Natural History, 2010).

In forensic facial reconstruction, the forensic anthropologist works with an artist (usually a sculptor) familiar with facial anatomy to interpret skeletal features that inform the decedent’s anatomical features as well as age, sex and ancestry (Taylor, 2001). More recent technological advances have equipped the forensic anthropologist with laser tools to scan sculptures, busts and dentures (Science Daily, 2010) which when aided with the use of computer software like CARES (Computer Assisted Reconstruction and Enhancement System), enable more precise plastic three-dimensional reconstruction speedily (Nafte, 2000; Science Daily, 2010).

Conclusion

Forensic anthropology is rooted in Darwin’s theory of evolution which explains human physical features as having evolved gradually over time to enable man to adapt to his environment for survival. Physical anthropology is the study of this evolution of man as it relates to biological change. One specific area of physical anthropology that studies the physical growth, development and variation of human bones is osteology. When this is applied to a legal investigation it becomes forensic anthropology. The expertise of a forensic anthropologist is based on extensive knowledge and familiarity of the differences in skeletons within and between populations.

The forensic anthropologist seeks to provide an identity for osteological remains. In doing this, the forensic anthropologist sets out to establish certain facts about the decedent. These include: Whether the decedent was human; how many decedents there are; the sex, age at the time of death, race and stature of the decedent; the time of death, as well as the cause and manner of death. In other to establish these facts, a vast knowledge and familiarity of variation in human skeleton within and between populations are employed. Both direct observations and extensive measurements are made of the bones and compared to known samples. Recent advances in technology have made three-dimensional facial reconstruction of the decedent (where possible) a reality and a part of forensic anthropology. Forensic anthropology is used in many countries in criminal and civil inquiries.