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Forensic anthropology
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 digenesis 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.
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