Forensic anthropology is the sub-discipline that applies the principles and methods of physical anthropology to legal issues. Forensic Anthropologists have a multiplicity of skills that are used at the JPAC CIL. Prime amongst these is the ability to construct a biological profile from a set, or sets of, unknown, skeletonized remains. Biological profiles assessed from skeletonized remains are used in two ways, the first is to provide immediate supporting evidence for identifications, and the second is to provide a means of narrowing potential short lists of individuals.
The biological profile is a series of characteristics that an individual possessed during life, but which critically can also be determined from skeletonized remains after death. These characteristics consist of age, sex, stature, geographic ancestry, trauma and/or other conditions that were extant in life. Analysis of these characteristics, at the CIL, is undertaken by direct comparison of remains with standard physical, or graphic, exemplars or by the application of mathematical models developed from reference populations. Reference populations consist of data sets that have been collected from studies on living people, or from mortuary populations that have a record of the constituent individuals' demographic information.
The success of creating a biological profile is largely dependent on the preservation and/or condition of remains at the point of their accession into the CIL. Some environmental conditions are particularly detrimental to the preservation of bones and teeth (although teeth usually survive for longer than bone). The jungles of Southeast Asia (because of widespread acidic soils and varying humidity) epitomize this problem - being very damaging to the preservation of human hard tissues. In addition, circumstances of loss can also inhibit preservation - the crash of a jet aircraft and its accompanying fragmentation and sometimes explosion and/or fire can result in the forceful breakup of the human body. These fragments present a much larger surface area for all of the vectors of decomposition and diagenesis to act upon.
For the majority of their casework, Forensic Anthropologists at the CIL work in the blind. This means that they have no prior knowledge of the case (e.g., aircraft type, names of personnel, number of crewmen, etc.) that might bias the results of any analysis. Information that is essential to the application of relevant anthropological models is not withheld. For example, modern populations are known to have changed in stature over time (on average, modern Americans are taller than Americans that lived in the past). This phenomenon is part of a complex issue known as secular change. Its implication is that models for calculating stature based on populations that were alive in the first half of the twentieth century (or even earlier) may not be applicable for calculating stature from a set of remains believed to have died recently. Thus a broad date of death is usually supplied to analysts to allow them to apply methods based on appropriate reference samples/populations.
Since the methods of physical anthropology are based on reference populations, the construction of the biological profile is undertaken in a set sequence. This sequence of analysis allows an analyst to select appropriate models and exemplars through a series of sequentially nested contingencies. The sequence of analysis followed is assessment of ancestry, followed in turn by biological sex, age, stature, and individuating characters.
The first criterion to be assessed is the geographic ancestry of an individual. Military records, in the past, contained a classification of personnel into the classical tripartite anthropological racial groups - Negroid (of African ancestry), Mongoloid (of Asian ancestry), and Caucasoid (of European ancestry). To ensure that the results of modern analyses are directly comparable to past records the CIL's Forensic Anthropologists, while acknowledging that human biological diversity is considerably more complex, still classify unknown service personnel into these antiquated divisions of humanity. The criteria that the scientific staff utilizes to make these classifications are based on non-metric and metric characters. Metric characters are those that lend themselves to being measured along a continuous scale. A distance between two hypothetical points can be measured on a continuous scale - the scale can be subdivided infinitely. In practice, pragmatic units for the scale of measurement are chosen, e.g., millimeters and tenths of millimeters are usually used in physical anthropology but kilometers or miles could be used (although it would be very inconvenient to work with the very small fractions of these large units). The two hypothetical points can also lie anywhere along the continuous scale. Examples of metric characters in forensic anthropology are direct dimensional measurements of the skeleton. For the assessment of geographic origin, metric characters of the skull have been found to be effective at classifying individuals.
Non-metric characters are those characters that have an expression that does not lend itself well to direct measure with a continuous scale. Non-metric characters are sometimes described as presence/absence traits (i.e., either an individual has the trait or they do not), but usually the morphologies of the skull that are used to assess ancestry are more complex than this, showing a multiplicity of forms. In combination, the assessment of metric and non-metric characters by a trained anthropologist is highly successful in classifying complete crania. The metric approach is less powerful once crania are fragmented and the non-metric approach becomes less and less useful with increasing fragmentation and absence of material.
The second criterion to be assessed is the biological sex of an individual. Humans, like most other primates, are sexually dimorphic. This is usually apparent from the primary and secondary sexual characteristics of the soft tissue. Although the hard tissues express dimorphic characters they are less obvious than those expressed in the soft tissue. At the onset of puberty, the female skeleton - especially the pelvis - begins to change shape. This is in reaction to the presence of newly secreted hormones, and is to allow females to give birth by expanding the pelvic outlet. The male skeleton also reacts to hormonal changes at puberty, but this is largely in parallel with increased muscle mass and the subsequent effect of increased forces on the skeleton. The assessment of biological sex focuses on these newly developed morphologies, focusing on the most dimorphic areas: the pelvic bones and the bones of the skull. Again a combination of metric and non-metric characters can be used to make these types of assessment. Metric characters rely on the fact that males are usually larger than females. Non-metric characters of sexual dimorphism rely on the fact that human sexual dimorphism is a binary scale (i.e., either male or female).
Metric characters can be problematic because larger (robust) females and smaller (gracile) males have a tendency to be misclassified. For this reason, non-metric characters are usually given more weight in the assessment of biological sex, although even these characters can vary greatly in their expression between individuals and populations. It is largely because of this variation in the expression of skeletal dimorphism by population group that the assessment of biological sex is subordinate to the assessment of ancestry.
The third criterion to be assessed is age. Assessing the age of individuals that have not reached skeletal maturity (i.e., before the skeleton has ceased growing) is relatively easy in comparison to ageing adult remains. This is because the vertebrate skeleton, including the teeth, follows a fairly well understood developmental pathway. The majority of the skeleton (especially the post-cranial skeleton) follows what is known as the "diaphyseal growth model." Early in the development of an individual, bones that follow this model of growth initiate the appearance of bony tissue at either one, or more, centers. These "centers of ossification" are in turn surrounded by a cartilage-based precursor. Developing bones increase in size by gradually replacing the cartilage precursor with bone. Eventually a developmental pathway is initiated that also allows the formation of "endplates," also made of bone, which act as the surfaces of joints where the young bones articulate with one another. These endplates are separated from the main center(s) of growth by a layer of the cartilage precursor. As an individual increases in age, and subsequently grows, the cartilage-based precursor is gradually replaced by bone until the bone itself has reached its full adult size. Once this occurs, the entire cartilage precursor that separates the bony endplates from the diaphysis is replaced with bone. In other words, it fuses. The timing of the fusion of these endplates, or "epiphyses," has been studied in living populations - via the use of x-rays - and these "fusion events" continue up until the middle twenties, with a large number occurring in the later teenage years. The approximate chronology of these fusion events is used to estimate the age of a deceased juvenile. In a similar fashion, although the development of teeth occurs in a very different fashion to bones, they form and erupt in a relatively well-defined sequence that can be broadly associated with chronological time.
For individuals that have reached full skeletal maturity there are no sequential, developmental events that can be related to chronological time. This means that, currently the only way of assessing age is through the analysis of relative degeneration of the skeleton through time. Using reference mortuary populations various markers have been identified that show a progressive change through time. Unfortunately, because these are not under anywhere near as tight a control as developmental events they are far less reliable as indicators of chronological age. For this reason, ages based on degeneration are given as a point estimate with a range. The point estimate represents the average age of individuals from the reference population that had attained a defined stage of degeneration for a particular marker. Around the point estimate is a range, or confidence interval which reflects the variation of ages in the reference population around the point estimate for a given defined stage of a marker. Most ranges for assessments of adult age are large. This appears to be a disadvantage, but actually, when trying to search for missing people it is essential that potential candidates are not ruled out unnecessarily.
The fourth criterion of the biological profile is the assessment of stature. At the CIL estimating an individual's living stature centers around the relationship between the size of an individual's bones and their stature, as reported in their military records. Mathematical models developed using measurements taken from living people, from cadavers, and also from mortuary populations of individuals with a "known" height at death, approximate this relationship. Again, stature is given as a point estimate, which represents the average stature attained by individuals with a particular bone length (or combination of bone lengths), and a range that represents the variation around that average stature for people with a particular measurement.
The last piece of the construction of the biological profile is the analysis of any existing traits of individuation. Whereas the previous components of the biological profile are present in every human, and thus derived from population studies, traits of individuation (e.g. trauma, pathological conditions, anomalies, etc.), as the term suggests, are not present in all humans. It is their relative infrequency that makes these characteristics so useful for providing strong circumstantial evidence of an identification, and occasionally even sufficient evidence for a positive identification.
When traits of individuation are recognized, two criteria must be met to make a trait potentially useful for identification purposes. First is its relative rarity. The more uncommon the trait the more potential it may have in contributing to identification. Unfortunately, the frequency of different traits of individuation is rarely precisely documented in the clinical literature. Second is the relative likelihood of a trait being recognized in vivo and subsequently documented. Uncommon traits in a skeleton without a corroborating record are merely points of academic interest.
Once the biological profile for an individual is constructed, the Forensic Anthropologist submits their illustrated final report to the Scientific Director to enable them to draw together all the lines of evidence that may help to support an identification. Like all of the reports by the Scientific Staff of the JPAC CIL, these reports are subjected to intensive internal and external peer review.
The biological profile of a set of remains is also used to improve any potential short lists of possible candidates for identification. This type of activity is particularly important for the recovered remains of individuals that went missing as ground losses during the Korean War. In this theatre large numbers of individuals went missing over periods of days when record keeping was a very low priority, because United Nations troops were on the retreat. Even though the J2, or records section of JPAC, may be able to immediately associate a recovered individual to a loss event based on geographical location of recovery, there may be several hundred potential individuals associated with that particular incident. There is also the possibility that an individual died many miles from where they went missing. In these types of circumstances making an identification of a given set of remains requires narrowing the identification short list - the set of potential individuals that a given set of remains could be. This is usually done through the use of the biological profile, but this type of situation exemplifies the problems of applying the techniques of forensic anthropology to identifications of particular sections of a population. Members of the armed forces (at least until fairly recently) were all young men, probably between 65 and 72 inches tall. This lessens the ability of the CIL's staff to differentiate between potential candidates. If this is the case the analysis of any material evidence that may accompany a set of remains may also assist in narrowing the short list. This allows the CIL to request relevant family reference samples for mtDNA sequence analysis and hence can considerably shorten the length of time that an identification takes.