Forensic Anthropology

Forensic anthropology is the specialized subdiscipline of physical/biologic anthropology (eg, the study of human and nonhuman primate anatomy, evolution, behavior) that applies the techniques of osteology (eg, the skeletal system on a macroscopic and microscopic level) and archaeology (eg, analysis of material culture from geographic features to artifacts) to the analysis of human remains in order to obtain findings that shed light upon the following ^{[1, 2]} : 

• The identification of human bone

• The determination of the biologic profile of the unknown skeletal remains

• The determination of a positive identification via comparison with antemortem and postmortem medical records and radiographs

• The types of trauma that were inflicted on the osseous and cartilaginous remains

• The order in which the traumatic events occurred

• When death occurred

• Finding the location of the surface scattered or buried bodies

• How to proceed with the excavation and recovery

• The numbers of individuals represented by the remains

As such, forensic anthropologic casework involves the investigation of deaths that are of legal and public concern and that typically culminate in expert witness testimony. ^[3] Although the use of forensic anthropologists in medicolegal and civil cases has steadily increased over the last 20 years, most forensic anthropologists are employed full time in education or research settings while working as consultants on a case-by-case basis. ^{[4, 5]}

However, the trend has been changing as forensic anthropologists have found work within the following:

• Coroner and medical examiner offices (eg, New York City [NYC] Office of the Chief Medical Examiner)

• The Armed Forces (eg, Joint Prisoners of War, Missing in Action Accounting Command / The Central Identification Laboratory, Hawaii ([JPAC-CILHI])

• Other governmental agencies (ie, National Transportation and Safety Board [NTSB], Disaster Mortuary Operational Response Team [DMORT], the Federal Bureau of Investigation [FBI])

• Nongovernmental organizations (ie, the International Red Cross, Physicians for Human Rights [PHR], and the Guatemalan Forensic Anthropology Association [FAFG])

Whether consulting as a forensic anthropologist on a full-time or ad-hoc basis, the American Board of Forensic Anthropology (ABFA) has been primarily tasked with regulating the field (since 1977) through the following stated objectives ^[6] :

• To encourage the study and practice of forensic anthropology, establish scientific standards, and advance the science of forensic anthropology

• To promote a high standard of ethics and professional conduct

• To issue certificates to eligible individuals

• To inform government and private agencies of the activities of the ABFA and its certified members

• To maintain lists of individuals who are ABFA certified and available for professional employment

See also the following:

• Postmortem Changes

• Postmortem Radiology and Imaging

• Forensic Entomology

Remains analyzed by forensic anthropologists are not always skeletonized. In many instances, human remains that have decomposed to an extent that precludes visual identification by the legal next of kin and/or fingerprint identification become forensic anthropology cases. Often, these badly decomposed cases need analysis for trauma and estimation of time since death in addition to identification. Therefore, forensic anthropologists tend to render the remains via maceration. ^[5]

Once the remains are skeletonized, the process of meticulous analysis begins and may include the collection of the following lines of evidence:

• Skeletal inventory to determine the minimum numbers of individuals represented by the remains ^[7]

• Anthroposcopic data and comparison with known age, sex, ancestry, and pathologic or trauma standards ^[8]

• Metric data using the University of Tennessee's Discriminant Function Database (FORDISC 3.0) to establish statistical validity of sex, ancestry, and stature findings ^[9]

• Radiographic data collection to document radio-opacities consistent with gunshot wounds or sharp force trauma, dental restorations and other surgical implants, and general skeletal morphology ^{[10, 11]}

• Recovery of surgical implants or medical devices with unique identification numbers ^{[12, 13]}

• Histologic data used in the analysis of age at death, pathologic conditions, and taphonomic (postmortem modifications to bone) change

• Radiocarbon dating to determine whether the remains are modern (of forensic significance) or archaeologic in nature ^[14]

• Facial approximation (the 2-dimensional [2-D], 3-D, or computer-generated reconstruction) or superimposition of antemortem with postmortem photographs ^[15]

• Stable bone carbon and nitrogen isotope data ^[16]

Every forensic anthropologic case is different, and many do not lend themselves to the collection of all of the lines of evidence listed above, because most of the human remains are traumatically incomplete, missing many of the 206 adult bones found in an intact adult skeleton. Nevertheless, what follows are overviews of the most accepted means by which forensic anthropologists collect their data in order to arrive at an identification of unknown human remains, establish time since death, and/or conduct trauma analyses of legal significance.

According to Walsh-Haney et al, approximately 20% of their forensic anthropology casework involves analysis of nonhuman remains. ^[5] The nonhuman remains may consist of an isolated deer bone found by children playing in the woods or pig bones collected by crime scene investigators, in addition to the human remains, found during a large-scale forensic scene recovery. In these instances, quick identification of nonhuman remains primarily arises from knowledge of human adult and juvenile skeletal anatomy.

Awareness of the two major distinctions of bone—maturity and shape differences—will help one to sort human from nonhuman bones. ^[17] For example, immature human bones can be differentiated from mature nonhuman bones of similar size and length, because the immature human bones will lack the superior and distal joint surfaces (eg, epiphyses). The nonhuman bone will have intact epiphyses, which tend to have smooth surfaces.

Furthermore, adult human bones tend to be less robust, with smaller sites of muscle insertion relative to all other animal species. When viewed in cross-section, the compact bone of quadrupedal vertebrates (eg, deer, pig, dog, and cow) tends to be thicker, relative to the bone's medullar cavity, than the cortical bone of humans (see the following image).

The cortical bone of quadrupedal vertebrates tends to give the bone a smooth, chinalike appearance relative to human bones. Bird long-bone shafts can be easily identified by cross-section, because they are thinly walled with cortical bone and have struts running down the medullar cavity.

The authors' experience has shown that the most commonly encountered nonhuman bones brought to medical examiners' offices include the following, in descending order of frequency:

• Pig (Sus scrofa) ribs and femora

• Deer (Odocoileus virgianianus) metapodials

• Cow (Bos taurus) ribs and vertebrae

• Fragmentary turtle (Emydidae: water/box turtle family; Cheloniidae: sea turtle family) carapace and/or plastron

• Bird (Gallus gallus: chicken; Meleagris gallopavo: turkey; Larus: gull)

• Fish vertebrae

• Dog (Canis familiaris) mandibles and long bones of the fore and hind limbs

• Raccoon (Procyon lotor) fragments of entire skeleton

• Bear (Ursus americanus) paws

The identification of the most commonly encountered nonhuman bones is briefly discussed below.

Isolated pig ribs and femora usually present with butcher marks, including spiral cuts—the latter usually appear in higher frequencies around holidays when spiral cut ham is plentiful.

Cow vertebrae often present with butcher marks, and they tend to have very sharp transverse processes and vertebral bodies that are convex on the superior aspect (procoelous) or concave on the inferior aspect (opisthocoelous). Human vertebrae have bodies that are flat on the superior and inferior surfaces (amphiplatyan) (see the image below). In general, nonhuman vertebrae never present with superior and inferior flat vertebral bodies.

When field dressed, deer metapodials may be left in the woods to rot and tend to show evidence of sharp force trauma. The metapodials can be quickly identified as a shaft that has a long groove that runs down the anterior and posterior midline aspects of the shaft (see the following image); human long-bone shafts do not present with a midline groove.

Fragmentary turtle shell will present with very busy and interdigitated sutures, whereas human cranial fragments have comparatively more subtle interdigitation at the sutures and a cross-section that presents with distinct inner and outer cortical tables that are separated by diploë (spongy bone).

If the bone in question is fragmentary or abraded in a way that obscures analysis of maturity and shape, histologic analysis is recommended. The thin sections of bone, when evaluated microscopically, may reveal plexiform bone. ^[18] Adult humans do not tend to present with plexiform bone. However, the histologic analysis of plexiform bone will not differentiate juvenile human bone from nonhuman bone. Rather, DNA analysis should be conducted.

The differences between male and female skeletons can be observed through anthroposcopic analysis of the skull and ossa coxae (ie, the ilium, ischium, and pubis)—differences which result from a combination of population-specific, sexual dimorphic, and evolutionary obstetric changes, respectively. Female skulls present with the following traits: tall frontal, slight, and relatively flat brow ridges; narrow and short mastoid processes; smooth occipital nuchal regions; and a chin that is most prominent on the midline. Male skulls tend to have sloping frontals, well-developed brow ridges, wide and long mastoid processes, robust occipital nuchal regions, and bilobed chins. ^{[4, 19, 20]} See the following image.

The trend of sex-related size differences observed on the skull are more easily evaluated on the ossa coxae. Specifically, the female pubis is broad, presents with the ventral arc and ischiopubic ramus ridge, whereas the ilium is broad, with a wide greater sciatic notch. In addition, when the pubic bones conjoin at the symphysis, a broad subpubic angle can be seen. Male ossa coxae exhibit the opposite trends, such as a narrow pubis, lack of the ventral arc and ischiopubic ramus ridge, and the ilium is less broad with a narrow greater sciatic notch. See the image below.

In addition to anthroposcopic analysis, metric analysis is often conducted in order to quantify the observed sexual dimorphic differences or to analyze other postcranial bones (ie, scapula, humerus, femur, tibia, sacrum, metatarsals, and calcaneus) when the skull and ossa coxae are unavailable for analysis. Calibrated sliding calipers, spreading calipers, osteometric boards, and mandibulometers are used to record the measurements (mm), and those data may be analyzed using the University of Tennessee's Discriminant Function Database (FORDISC 3.0).

Estimation of living height from skeletal remains can be determined via sex-specific, ancestry-specific, or sex-ancestry specific regressions via the University of Tennessee's Discriminant Function Database (FORDISC 3.0) program. The formulae provided by the FORDISC 3.0 estimate statures as an interval (as a mean with standard errors). Postcranial bones including femur, tibia, sacrum, humeri, radius, ulna, and calcaneus may be included (in any combination) in the regression that is generated by the program. Metric data are collected via spreading calipers, sliding calipers, and an osteometric board.

An alternative metric assessment, the Fully method, includes cranial height and vertebral body height in the calculation. ^[21] However, the Fully method is used less in forensic contexts, because complete skeletons are not always recovered.

Certain regions of the world have been grouped together, via clinal distributions, into what has traditionally been called ancestry groups or ancestry affiliations. Some individuals are highly representative of the clinal archetype of a particular ancestry group, and other individuals are more difficult to classify.

It is important to note that there is greater variation in a particular trait within an ancestry group than there is between ancestry groups. In North American forensic contexts, individuals are generally divided into the following ancestry groups: African (black), European (white), Native American, and Asian. The latter two ancestry groups share a closer genetic history and have similar traits that are often grouped together (see the image below). ^[22]

Ancestral affiliation tends to be best estimated from the evaluation of anthroposcopic traits and metric assessment of craniofacial skeleton, cranial vault, and dental morphology (see Table 1, below) (see also the following image). ^{[22, 23]}

Metric assessment using University of Tennessee's Discriminant Function Database (FORDISC 3.0) quantifies each skull through the use of a battery of measurements that have been amassed using skeletal collections composed of individuals of known ancestry.

These same measurements can be collected for an unknown skull or cranium, and ancestry can be estimated using the program, which provides the posterior probability typicality, F-typicality, Chi-typicality, R-typicality, and ranking results for the unknown individual.

Table 1. Orbit, Nasal Aperture, Dental Arcade, Tooth, Suture, and Vault Shape Traits Organized by Ancestry Group (Open Table in a new window)

Using human skeletal remains, forensic anthropologists assist law enforcement personnel in identifying cold cases through aging. Because of changes that occur in bone over time due to disease and nutritional effects, forensic anthropologists often present "age at death" in broad age ranges; for example, 1-3–year span for sub-adults and 10-20–year span for adults.

In juveniles, five categories are examined to determine age at death, as follows:

• Epiphyseal union

• Length of long bones

• Union of primary ossifications centers

• Tooth formation

• Tooth eruption

For adults, an evaluation of the following will give an estimation of age at death:

• Auricular surface

• Sternal rib ends (4th rib)

• Pubic symphysis

• Cranial suture closures

This section discusses the aging methods used to evaluate fetal and sub-adult skeletal remains.

Epiphyseal union

Most bones are preformed in cartilage that is gradually replaced by a hard bony matrix. This process occurs throughout gestational development into young adulthood. For example, the limb bones consist of one shaft (diaphysis) and two ends (epiphyses). These ends are connected to the shaft by a cartilaginous growth plate (metaphysis) that is replaced with bone when growing stops naturally or is arrested by poor health.

Because the timing of bone growth and fusion tends to be predictable, age can be traced through the union of joints. ^[24] In a healthy individual, fusion tends to occur first at the elbows (9-14 y), ^[25] then proceeds to the hips, ^[24] ankles, ^[26] knees, ^[27] wrists, ^[28] and lastly, the shoulders (by 18-22 y). The rate of fusion in the vertebral column can also be used for age estimation. ^[29]

Length of long bones and ossification centers

There is linear correlation between long-bone lengths and age for prenatal, natal, and early postnatal infants. ^[30] Developed research (Hoffman) has shown that an infant's age can be determined by discovering the length of its femur and the corresponding lunar month. ^[31]

Because bone is deposited in primary ossification centers at particular developmental times, a rough estimate of age at death can be determined through metric assessment of the primary centers.

Tooth formation and tooth eruption

Teeth undergo maturational changes in their size, shape, calcification, and eruption. ^[32] Teeth begin as deciduous tooth buds (in utero through 3 y) and push through the gums as fully formed deciduous crowns and roots (3-6 y). Complete replacement of the deciduous teeth by the permanent teeth occurs at about age 12 years (excluding the wisdom teeth or third molars). The timeliness of dental eruption varies depending on the sex, race, and overall health of the individual. In general, females tend to develop 1.5 to 2 years earlier than males.

The aging methods used to evaluate adult skeletal remains are reviewed in this section.

Auricular surface

Over time, the auricular surface of the os coxa will display age-related changes. These changes, categorized in eight phases, can be studied to determine an age range, as summarized in Table 2, below. ^{[33, 34]}

Table 2. Age-Related Changes Involving the Os Coxa Auricular Surface (Open Table in a new window)

Pubic symphysis

Age determination techniques have been developed to enable the forensic anthropologists to study the surface of the pubic symphyseal face and the ventral and dorsal margins and gain an age range. The analyses of pubic symphysis can be divided into six ^[35] or 10 phases. ^[36] The topography of the symphyseal face can range from rugged, well-marked with horizontal grooves for a teenager to a depressed symphyseal face with irregular ossification for a senior citizen (see the image below).

Sternal rib ends

The part of the sternal rib end that is connected to the sternum via cartilage experiences changes (ie, life stresses) throughout an adult's life. Due to these changes, the rib ends endure modifications, as summarized in Table 3, below. These modifications to the rib ends can sometimes give forensic anthropologists an approximate age range. ^{[37, 38]}

Table 3. Iscan and Loth Rib Aging Descriptions (Open Table in a new window)

Additional adult aging methods include microscopic analysis of cortical remodeling (best for individuals older than 40 y ^[24] ), bone and tooth histology, ^[39] and radiographic analysis for the detection of loss of bone density. ^[24]

Cranial suture fusion

Cranial suture fusion can be used when other macroscopic methods are not possible. ^{[24, 40]} However, cranial vault suture fusion tends to have variable results and should only be used when other methods are not possible. ^[41] By contrast, age determination by way of maxillary suture fusion is considered very reliable. ^[42]

The timing of a traumatic event is important for the reconstruction of the physiologic events that caused death which, in turn, provide the coroner or medical examiner with information that may help in the determination of manner of death (ie, natural, homicide, suicide, accidental, or undetermined). The manner of death is a medicolegal finding by the medical examiner or coroner.

Forensic anthropologists do not determine manner of death. Consequently, a forensic anthropologist evaluates the skeletal remains by noting the location, type, and extent of the skeletal injuries and whether the pathologic or traumatic injuries were present in life (antemortem), perimortem (at or around the time of death), or after death (postmortem). ^[43]

Antemortem trauma

Antemortem trauma and pathologic change may be observed in bones and teeth via macroscopic, radiographic, and or microscopic means. In general, the determination that the disease or injury occurred antemortem is identified through the presence of bone cells (osteoblasts, osteoclasts, and osteocytes) which mark the location of infection and healing. For example, an antemortem wrist fracture may be identified by cellular bridging of fracture margins (a soft callus), followed by the creation of the hard callus, which stabilizes the fracture, and remodeling, which shapes the injury site to its original conformation. The rate at which healing occurs depends on the lesion location and the overall health of the individual. Furthermore, the location of the injury or pathologic response may be compared to medical records or radiographs to determine a positive identification. ^[44]

Perimortem trauma

Perimortem trauma is observed when there is no evidence of healing on the bone. Forensic anthropologists tend to be most often consulted on cases involving perimortem trauma, such as injuries caused by bullets, blades, and bludgeons.

Bullet wounds vary, depending upon the bone affected and the ballistic characteristics of the projectile. In general, a gunshot wound (GSW) entrance is beveled internally, whereas an exit wound exhibits outward beveling. ^[45] Atypical defects may result when the bullet strikes the bone tangentially. More extensive fracturing occurs from high-velocity projectiles. Nonjacketed bullets typically produce a lead smear that can be seen radiographically.

Blade strikes leave characteristic marks on bone, which include V-shaped notches (that represent the blade of a knife) and U-shaped, or square, compression injuries (that may indicate the spine of a blade). The blade may leave microstriae on the bone, which can be matched to the exact blade used to cause the injury. ^[46]

Blunt force injury results in fractures that take the path of least resistance. The fractures will propagate until the energy is dissipated. Mechanisms of injury include items such as baseball bats, rocks, and rapid deceleration trauma from motor vehicle accidents. Manual strangulation may cause hyoid fractures and/or fractures to the thyroid cartilage. ^{[47, 48]}

Postmortem trauma

Postmortem trauma and taphonomic changes result from environmental-, human-, mechanical-, and animal-induced processes that alter the remains after death. Understanding the markers of postmortem trauma and taphonomic change is necessary, such that postmortem fractures attributable to scavengers are not confused with perimortem defects.

Environmental factors that affect the decomposition rate and alter the skeleton include average daily temperature, rainfall, humidity, substrate or soil pH, insects, vegetation, and animal scavengers. These environmental factors may speed up or slow down decomposition, disperse the corpse or bones over a wide area, and damage bone. The sun, soil, and water can crack, flake, and splinter bone. Water transport may break off pieces of bone that protrude or smooth the bone's projections. ^[49]

Animal scavenging, from dogs, raccoons, rats, and buzzards, tend to cause disarticulation of the skeleton and may be identified through punctures, parallel grooves, and/or pits. ^[50] Scavengers often leave puncture marks on the orbits, sternal ends of ribs, vertebral bodies, and the ends of long bones. Additionally, carnivorous scavengers can create spiral fractures, which twist around long-bone diaphysis.

Human factors can cause breakage, fracturing, polishing (as in patina caused from extensive handling of a specimen), and splintering. This type of taphonomic change can occur when picking up a bone in order to inspect it, cutting through the bone with a shovel or backhoe during the excavation process, accidentally stepping upon the remains during a surface recovery, or removing the calotte during autopsy. ^[51]