Forensic anthropology is the application of anthropology to criminal investigations. It incorporates concepts and methods from biological anthropology (the study of the physical aspects of humanity).
Identifying unknown individuals is a key part of forensic anthropology. Anthropologists assist in identifications primarily by constructing a biological profile. This includes estimating age, sex, stature, and ancestry, as well as identifying specific characteristics, like diseases or injuries. In addition to helping identify human remains, the anthropologist analyzes injuries that happened around the time of a person's death, which can help determine how a person died. To do these things, an anthropologist begins by asking a series of important questions.
Is it bone?
The first thing the examining anthropologist must determine is whether or not the material is bone. A surprising number of other materials may be mistaken for bone on first glance, especially if they are covered with dirt or other substances. Ceramic shards, plastic, wood fragments, rocks, small bits of concrete can all be mistaken for bones or bone fragments. To ensure the material is bone, the anthropologist cleans the object and examines it closely, under magnification if necessary.
Is it human?
Once the anthropologist is sure that the material is bone, they must determine whether it came from a human or a non-human animal. All mammals share a generalized skeletal template, meaning they all have the same bones in roughly the same locations: a skull, spine (which ends in a tail), ribs (which support the internal organs), and four sets of limb bones. However, the shape of the bones and the way they relate to each other, differ between animals. By examining the size, shape, and structure of a bone, an anthropologist can determine if it is human.
What bones are present?
Once a case involves human bone, the investigator must identify which bones (or "elements") are present and which are absent. Most anthropologists start this process by placing the elements out on a table as they would be organized in a living person, known as the "anatomical position". This serves several purposes. First, it creates an informal visual inventory that allows any missing elements to be identified quickly. Also, it allows the analyst to work systematically through the entire skeleton, performing a detailed inventory and examining each bone for trauma, pathology, or life history traits. Lastly, after examining each bone, the analyst can consider the skeleton as a whole, and look for inconsistencies among elements or patterning of trauma across multiple elements.
At a recovery site, skeletal inventories are important because they allow searchers and scene responders to know what they might be looking for that they have not already recovered. This ensures they make as full a recovery as possible. Inventories are also important from a criminalistic perspective for establishing what elements are or are not, present. The absence of certain elements can provide a great deal of information regarding perimortem events, taphonomy, and perpetrator behaviour.
How many people are represented?
In addition to establishing which elements are present, anthropologists must determine the number of individuals involved. To do this, they look for duplicate elements - for example, two right femora (thigh bones). Investigators also consider the condition and size of the bones. If the elements do not "match", it could suggest more than one individual. When the remains of two or more individuals are mixed together, this is called "comingling". It is the anthropologist's job to address the comingling and determine which individuals are represented by which bones. This allows each body to be examined separately.
Establishing the number of individuals is very important, especially if the case involves a crime. Multiple individuals may be killed together or separate victims may be dumped in the same place over a longer period of time. Sometimes perpetrators may bury many victims together in a mass grave in an attempt to conceal their behaviour. In all cases, it is very important to the understanding and resolution of the case that the anthropologist be as accurate as possible about how many victims were involved.
Are the remains modern or ancient?
First Nations and Native American people have occupied North America for thousands of years. Over time, these groups moved in and out of their territories and often buried their dead along the way according to the current customs. In some cases the burials were not marked, in others the graves were commemorated, but the markers have since decayed or disappeared. Today, these ancient graves are sometimes accidently exposed by rain, soil erosion, or human activity. As specialists in the study of human remains, anthropologists are often called upon to distinguish ancient burials and remains from modern deaths of forensic significance. If a set of remains is determined to be archaeological, the cultural group most closely associated with that burial is notified so the remains can be handled in an appropriate manner. The remains are usually returned to the tribe for reburial. However, if the skeletal remains are clearly recent, they are treated by law enforcement and the Coroner's or Medical Examiner's office in the same manner as any other unattended death.
Anthropologists can often tell the difference between an ancient and modern skeleton by the context of deposition. This includes the location, position, and condition of the body, and gives clues to the events which led to its burial. Associated material evidence can also suggest the origin of a set of remains. Obviously, remains found with modern clothing, a mobile phone or mp3 player in the pocket, and modern dental work are those of a person who died very recently. On the other hand, skeletal remains found in association with cultural objects consistent with local First Nations burial practices are likely to be those of a person buried according to his or her cultural and social heritage and are therefore not of forensic interest.
Who is the individual
Anthropologists contribute to the identification of unknown individuals by developing a biological profile: age, sex, stature, and ancestry. In addition, the biological profile includes information that may be particular to that person and no one else, such as diseases or injuries which may impact the bone.
The first step in developing a biological profile is to determine sex. Sex is the biological aspect of an individual, determined by genes, and expressed through primary (e.g. reproductive organs and hormones) and secondary (e.g. musculature, body hair, etc) sexual characteristics. In contrast, gender refers to the social expression of a person's identity as it relates to their social role and behaviour. Gender is generally self-defined. Societal and cultural norms may influence gender choice, but an individual may not necessarily identify themselves according to those rules. In general, anthropologists do not determine the gender of an individual, but personal effects and cultural materials may suggest a person's gender identification.
The hormonal and visual differences that make living males and females distinct also create physiological differences between their skeletons. This "sexual dimorphism" is most obvious in the pelvic bones and the skull. The differences in the pelvis are largely the result of evolutionary and functional constraints. All humans are adapted to walking on two legs, but females must also give birth to relatively large-headed babies. These different pressures produce structural differences between males and females that can be used to tell them apart.
The skull also displays a degree of sexual dimorphism. Overall, males tend to have larger skulls than females. They also have, on average, greater muscle development and more rugged muscle attachments. These differences in size and robusticity can help determine whether an individual is male or female.
Differences in size and robusticity may also be evident in other elements. If the skull and pelvis are not available, measurements of other bones may help determine if an individual is male or female. However, investigators must be cautious, as there is considerable overlap between males and females.
Estimating a person's age at the time of death depends on two fundamental life processes: growth and decline. Growth and developmental changes are based largely on the degree and location of bone growth and dental formation and eruption from the gums in immature individuals. At birth, our "bones" are mostly soft cartilage. As we grow, this cartilage is replaced by hard bone at different centers of growth. There are over 300 centers of bone growth in infants which eventually fuse to form the 206 bones in the adult body. Since the centres grow and fuse at known rates, anthropologists can use the pattern to estimate age in children and subadults. Similarly, teeth develop and erupt in a specific sequence at specific times during childhood and this timing can also be used to provide an accurate estimate of age in juveniles.
Figure 1: Developmental stage differences between (from left to right) 6 months, 6 years, and 8 years of age . Notice the appearance of little bones at the end of longer bones in the middle and right photo: as we get older, these will fuse together to form a single bone. The appearance and fusion of these bones helps anthropologists determine the person's age.
Figure 2. This is an x-ray of a young person's knee. Notice the lines between the longer shafts of the bone (the diaphyses) and the tips (the epiphyses). During childhood and the teenage years, the diaphysis and epiphysis will fuse together.
By the late-20s however, bone growth is complete and age at death must be estimated from degenerative changes in the body. Joints are particularly prone to deterioration and a common area to use for age estimation is the pelvis. At the front of the pelvis, where the two halves meet above the pubic area, is a joint called the pubic symphysis. This joint undergoes consistent changes over the course of a person's lifetime that can be used to indicate physiological age (see Figure 2). The fourth rib is also used to estimate age as the cartilage between the end of the rib and the sternum slowly turns to bone over time. Finally, it is also possible to use features of the skull to estimate age. Although it appears to be a single unit, the skull actually consists of multiple bones held together by zipper-like fusions called sutures. These sutures are more "open" and loose in younger individuals, but by the time most individuals reach old age the sutures are fused and almost invisible.
Figure 3: Developmental changes to the pubic symphysis, over six stages (I-VI) from younger (on left) to older (on right).
Anthropologists also attempt to identify ancestry as part of a biological profile. In our society, the term "race" is often used to refer to population differences. However, races do not exist in the biological sense and anthropologists prefer the term ancestry. To assess ancestry, anthropologists look for skeletal features that tend to be more common in some populations than others. They cannot determine skin or eye colour, but they may be able to place an individual into one of three broad geographic categories: European, African, or Asian. Importantly, while people with similar ancestry tend to share certain characteristics, humans vary more within populations than between them and there is a high degree of overlap. It is also important to remember that in forensic investigations, recognition and identification are the ultimate goals and ancestry often has more to do with a person's physical appearance than their biological heritage. Ancestry is estimated by measuring, observing and analyzing the bones of an individual's face and skull.
Estimating living stature can also help identify an unknown individual. Because there is a close relationship between limb length and height, anthropologists can measure the arm and/or leg bones, and put the measurements into a mathematical formula that accounts for variation by sex and ancestry group. The formula then produces a height range, which can be used to exclude individuals that fall outside those limits.
Specific physical characteristics are also helpful in the identification process. Genetic or nutritional disorders, diseases and infections, or healed fractures all alter the bone in unique ways that can be used to distinguish individuals or to compare with antemortem medical records of missing persons to find potential matches.
Genetics can play a part in the unique characteristics of an individual's skeleton. For example, a genetic disorder called Osteogenesis Imperfecta ("brittle bone disease") leads to repeated bone fractures. These fractures will appear on the skeleton in many locations and in varying stages of healing. Because the condition requires ongoing medical attention, an affected individual will likely have extensive antemortem medical records that could aid in their identification.
Nutritional disorders can also leave telltale evidence on the bone. Dietary anemias (iron deficiencies) can cause swollen marrow space in bones, especially the flat bones of the skull. Vitamin C and D deficiencies lead to scurvy and rickets, respectively. Both conditions involve inadequate bone mineralization, causing bones to soften and eventually bend under an individual's own weight.
Neoplastic diseases such as cancers can affect the skeleton in two ways. Cancer in the soft tissue beside a bone can lead to pressure, causing the tissues to react and leaving visible lesions or holes in the bones. Other types of cancer cause the bone itself to grow tumours. Whether they are benign or malignant, bone tumours can cause significant skeletal changes that be identified long after the soft tissue has decomposed.
Infectious diseases can also provide information about an individual's life history. Tuberculosis is a bacterial disease that can cause lesions on the bone, especially the spine, ribs, and pelvic bones. Syphilis, a sexually transmitted bacterial infection, causes degenerative pits to form on the surface of the bone, and is most severe on the forehead, nose, and shin. Hansen's disease (also known as leprosy) is primarily a soft tissue disease. It affects the skin and nerves, and tends to present in the face and extremities first. While Hansen's disease does not directly cause bone loss, it can lead to tissue necrosis, which in turn causes atrophy and degeneration of the bones in those areas.
Fractures are another feature of life history that can contribute to identification. Bones broken during life heal, but often retain evidence of the healing, similar to a scar on the skin. If the fracture was severe and required medical intervention, surgical hardware such as metal plates, rods, and/or screws may be present. Some hardware possesses a serial number, which can be traced back to the manufacturer. This information can significantly narrow the list of potential missing persons. The same is true for prosthetics. Dentures, glass eyes, pace-makers, and artificial limbs are all specific and fitted to the individual using them. These are rare, but extremely helpful, individualizing characteristics.
Forensic anthropologists are also trained to examine evidence regarding the circumstances surrounding the death of an individual. This involves analyzing skeletal trauma and differentiating between injuries caused by bullets, sharp objects, blunt objects, or other instruments. Sharp force trauma results when a narrow or pointed object hits a very small area. The stabs, slashes, and cuts typical of sharp force often penetrate deep enough to leave cut marks on the bone. In contrast, blunt force trauma results from a larger implement hitting a much broader area. Blunt force trauma can cause fractures of the arm and leg bones or crush and shatter the flat bones of the skull. Projectile trauma involves a high force applied over a very small area. Projectile trauma can involve bullets, arrows, spears, or any other small object delivered at high velocity. The damage caused by projectile trauma can often be used to indicate the direction of travel of the projectile. Other forms of trauma that an anthropologist may find evidence of include strangulation, electrocution, chemical or heat related trauma, or explosions.
In addition to the injuries themselves, the patterns of injuries present on a body can be very important to the case. Multiple, severe blunt injuries over the whole body may suggest a fall from a great height or a car accident. Sharp force injuries to the hands and lower arms are indicative of defence wounds. The direction of projectile wounds can also be used to support or refute a suspect's story. It is the anthropologist's task to carefully record all traumata according to type, location, and number to reconstruct the overall picture of what happened to a person at the time of their death. And although they are not legally responsible for determining cause of death, the information anthropologists collect can help the coroner or medical examiner make their official judgement on the case.
When did it happen?
Whether it relates to an accident or a crime, the timing of an incident is an important aspect of any investigation. To address the question of elapsed time since death, anthropologists use taphonomy to understand the context and conditions which alter human remains. This includes all the biological and non-biological processes that contribute to the decomposition, skeletonization, and depositional changes associated with a set of remains. Biological factors include human agents, animals, plants, insects, and invertebrates. Carnivore scavenging of fresh remains and rodent gnawing of dried remains are common. Plant roots can etch into bone surfaces while insects and worms can move remains during tunnelling and nest-building. Low soil pH, wind, water, and sand are all capable of abrading bone surfaces. Repeated freeze and thaw cycles can reduce a bone to fragments while intense heat and sun can cause the surface of bones to crack and peel away. Using their knowledge of taphonomic processes, anthropologists can estimate the length of time a body has been buried or exposed, or determine whether a set of remains has been moved.
Confirming an identification
Once a biological profile has been created and a potential missing person singled out, investigators must try to ensure the unknown remains actually belong to the missing person in question. One of the best ways to do this is to compare antemortem medical records with the evidence presented by the remains. For example, radiographs ("x-rays") taken during life can be compared to radiographs of the skeletonised remains. Examiners look for http://www.googleartproject.com/ in size, shape, and features to determine if the antemortem and post-mortem radiographs could represent the same individual. Medical records of individuals with surgical implants such as pace-makers, breast augmentations, surgical steel orthopaedic pins, etc. can be correlated with the presence of similar objects recovered with remains.
Even though the information they provide may be instrumental to the case, anthropologists cannot legally identify an individual. In most of North America, the coroner or medical examiner is the only person legally able to make an identification. If all of the antemortem records, material evidence, and skeletal evidence agree, the identification is considered "presumptive". This means the investigators presume that the deceased is the missing person. At this point, investigators will seek corroborative evidence, often by requesting DNA samples from family members. If the familial DNA matches the individual's DNA, the identification is considered "positive". The remains are then returned to the family. In some cases however, DNA may not return sufficient results to confirm the identity of the individual, and the coroner or medical examiner must decide if all the evidence, taken as a whole is strong enough to support the identification.
A report is a formal description of an event or investigation. A forensic report explains what an investigator did, how they did it and what they think the evidence shows. A forensic investigator's report is especially important because it must be able to explain the results of the investigation to a judge and possibly a jury who would not be able to attend a crime scene and observe an investigation first-hand. There are no agreed-upon protocols or standards for writing forensic reports in Canada, but most forensic scientists use a scientific format that includes the following:
- Report summary
- Background (how the author became involved in the case)
- Qualifications of the author (what makes the author an authority on the subject)
- Materials, methods and limitations (what work was done, how and why it was conducted, and any barriers to further investigation/analysis)
- Results (what the evidence found)
- Interpretation of results (what the evidence means, within the area of expertise)
- Conclusions (another short summary of the case, the findings and their importance)
- Bibliography (what sources of information - professional literature, interviews etc - were used).