Forensic anthropology combines the theories and methods of anthropology, osteology and archaeology with legal investigations. The role of the forensic anthropologist can be varied, including aiding in the collection and analysis of human remains, the identification of victims beyond recognition, the estimation of time since death, and the establishment of injuries and potentially cause of death. The victims examined by anthropologists are usually in the late stages of decomposition, are completely skeletonised, or have been rendered otherwise unrecognisable by fire damage or other injuries.
The forensic anthropologist will sometimes be called in when suspected human remains are first discovered to aid in the excavation and initial analysis of the bones. Following the careful excavation, documentation and collection of the remains, they are cleaned up in preparation for the analysis. During the investigation, the anthropologist will conduct a variety of examinations and tests to determine various features to aid in the identification of the victim. Whilst studying the bones, it may also be possible to identify evidence of trauma which occurred prior to the fatal incident, acting as potential identifiers, or trauma which occurred during the incident, providing details as to the cause of death. Finally, the details of the anthropological analysis and any results are recorded in a detailed report for use in the investigation and potentially in court, at which point the expert may be required to stand as an expert witness.
Anthropologists are frequently involved in non-criminal matters, particularly as part of mass disaster teams. When natural disasters, plane crashes and explosions occur, there will often be a large number of unknown victims requiring identification. Additionally, their expertise is often called upon in the identification of remains held by universities and museums, often of a much older origin than remains relevant to legal matters.
Age of Remains
When human remains are discovered, it is possible that they are relevant to recent or current legal proceedings. However the presence of certain artefacts can suggest the remains are actually historic or prehistoric, rendering them irrelevant to legal investigations. Such items include coffin remains, arrow heads, and scraps of dated clothing. Carbon dating is a common method of establishing the age of bones or objects. The radioisotope carbon-14 is taken up by an organism in life. As the half life of carbon-14 is known as being 5,700 years, the amount of the isotope remaining in the sample can be used to calculate its age.
Whenever remains are discovered, before a full investigation ensues, it must first be established that the bones are of human origin. According to Bass (1995), up to 30% of remains seen by a forensic anthropologist are non-human. If the larger bones are present in a set of remains, it is generally much easier to determine whether they belong to a human or not. Smaller bones can provide greater difficulty, and will require great knowledge and experience on the part of the expert to confirm their origin. If the remains are deemed to be non-human, the investigation will generally come to an end, unless relevant to criminal proceedings.
One of the initial factors to determine when identifying a set of human remains is the sex of the individual. There are numerous features of the human skeleton that can be studied to help establish this, the most obvious being the pelvic bone. Women generally have proportionally wider pubic bones than men to allow room for a baby’s head to pass through during childbirth. In most cases a female will bear a sub-pubic angle of more than 90 degrees, whilst the sub-pubic angle of a male’s pubic bone will generally be less than 90 degrees. The use of the pelvic bone alone has proved extremely precise in establishing sex, with an accuracy of up to 95% (Byers, 2002). However this is not a useful indicator when determining the sex of a pre-pubescent child, as the pelvic bone in girls is yet to widen, thus meaning there is a lack of sexual dimorphism between the sexes.
The skull is equally beneficial in the establishment of sex. A male’s skull will generally have a more rounded supraorbital margin, or brow ridge, and a bony glabella, the portion of bone between the eyebrows and nose. The mastoid process, behind the ear, is larger, the mandible more squared, and the forehead slightly backwards-slanting. The nasal cavity of a male will be longer and narrower. In contrast, a skull belonging to a female will have a sharper supraorbital margin and a smooth glabella. The mastoid process will be smaller in size, the mandible less squared, and the forehead more rounded. A female will generally display a slightly wider, pear-shaped nasal cavity. Though slightly less accurate in identifying sex than the pelvic bone (80-90% using the skull, according to Byers (2002), the skull is still greatly beneficial in sex determination.
There are additional though less accurate points of identification. Males tend to have larger, heavier, and more rugged bones in general, with slightly larger ends to support stronger muscles. Sex is generally easier to establish if the racial background of the victim is known, due to differences between different ethnic groups.
A vital feature of identification is the age of the victim. By studying the appearance of condition of particular bones, it may be possible to estimate this, sometimes as accurately as within a few months.
As an individual ages, a process known as ossification occurs in around 800 points around the body, in which separate pieces of bone fuse together. As the bones fuse together, sutures are formed in between them, appearing as ‘zigzag seams’. The fusion of particular bones generally occurs at specific points in an individual’s life, making them invaluable in age determination. For example, at around the age of 6, two bone plates form at either end of the radius bone in the arm. The lower bone plate fuses with the radius years later, at age 17 in males and age 20 in females. The upper bone plate follows shortly after.
The fusing of the epiphysis (rounded end) of a bone to the diaphysis (bone shaft) are similar indicators of age. Growth centres within the limb bones allow the limbs to lengthen as the individual grows, thus increasing their overall height. Throughout this growth period, the epiphyses are soft, eventually hardening into bone and fusing with the main shaft as adulthood approaches. The head of the femur generally fuses between ages 18 and 20, and part of the hip undergoes the same process and around 24 years. After this point, the study of this fusing is fairly useless in age determination.
Though not particularly accurate, cranial sutures (on the skull) can aid age determination if no other methods are suitable. At birth, the human skull is composed of numerous smaller bone segments, their division giving the skull flexibility. As the individual ages, ossification occurs, fusing the separate pieces together. It is the extent to which this fusion has occurred that is useful in age estimation, provided the victim is under approximately 30 years old, after which ossification of skull bones is usually complete.
Similarly, certain sections of cartilage around the body gradually turn into bone over time, again usually at a particular age. For example, at birth the wrists are composed of cartilage, eventually forming into bone at a later date. If the victim is under the age of 13, a wrist x-ray can often pinpoint the child’s age within a few months.
Studying the pubic symphysis, the midline joint between the left and right pubic bones, can give an estimation of the age of the victim. The two pubic bones, joined by cartilage, are characterised by a rough, uneven surface which gradually smoothens out over time.
In particularly elderly individuals, worn teeth, signs of bone degeneration, arthritis, osteoporosis (increased bone porosity), and similar diseases can indicate old age. However the level of wear of teeth can be influenced by diet and cultural practices, so this should be taken into consideration. On the other hand, if dentures or other false teeth are found in or near the remains, this is a further sign of an elderly victim.
Osteon counting by microscopy is another method of estimating the age of a victim. Osetons are minute tunnels within the bone housing nerves and nutrient-providing blood vessels. In general, the more osteons present in the bone, the older the victim.
Tooth eruption can prove particularly beneficial in determining age, particularly in younger individuals. The presence of deciduous teeth, also known as milk teeth, suggests the victim is an infant or child, as these teeth tend to be lost by around age 12. Similarly, the lack of wisdom teeth indicates the victim is under the age of 18. The eruption and loss of specific teeth tend to occur at particular ages. By studying these teeth, it is often possible to pinpoint the age of the victim quite accurately. Below is a list detailing the age at which each tooth tends to erupt.
Primary (Milk) Teeth
Central Incisor: 8-12 months
Lateral Incisor: 9-13 months
Canine: 16-22 months
First Molar: 13-19 months
Second molar: 25-33 months
Central Incisor: 6-10 months
Lateral Incisor: 10-16 months
Canine: 17-23 months
First Molar: 14-18 months
Second Molar: 23-31 months
Secondary (Permanent) Teeth:
Upper:v Central Incisor: 7-8 years
Lateral Incisor: 8-9 years
Canine: 11-12 years
First premolar: 10-11 years
Second premolar: 10-12 years
First molar: 6-7 years
Second molar: 12-13 years
Third molar (wisdom tooth): 17-21 years
Central Incisor: 6-7 years
Lateral Incisor: 7-8 years
Canine: 9-10 years
First premolar: 10-12 years
Second premolar: 11-12 years
First molar: 6-7 years
Second molar: 11-13 years
Third molar (wisdom tooth): 17-21 years
There are a number of differences in the structure and appearance of bones between individuals of different races that can be observed and used in the establishment of a victim’s ethnic origin. The majority of these differences are based in the skull.
A Caucasian victim will generally display a narrower face and high-bridged nasal bone. The upper incisors will often have a flat lingual surface (surface closest to the tongue). The chin will often be more prominent and the cheekbones fairly flat.
A Negroid skull will often exhibit a broader nose bridge with wider nasal openings and subnasal grooves. The skull will often hold outward-sloping jaws, with the lingual surface of the upper incisors being flat.
The skull of a Mongoloid victim will be broader around the face, with squarer, forward-sloping, wing-like cheekbones and a lower nose bridge. Unlike Caucasians and Negroids, the upper incisors are likely to be shovel-shaped and the skull flatter.
Aside from the bones of human remains, the structure and colour of any remaining hair may also provide clues as to the ethnic origin of the victim, due to the variation in the morphology of hair between different ethnicities.
Despite these numerous points of identification, racial determination is not always obvious, particularly with the increasing likelihood of mixed-race victims. The remains of such individuals are likely to display signs of two ethnic groups, making the deduction of race much more difficult.
Stature, Weight & Individual Differences
When dealing with the remains of an adult woman, an examination of the pubic bone may be able to indicate whether or not the victim has given birth in the past. During childbirth, the area by the pelvic inlet widens, small indentations often being left behind, particularly after multiple children. The area around the pelvic inlet will widen for childbirth, and may not fully contract back to its original size.
There are numerous methods available to determine the stature of the victim. If the skeleton is whole, direct measurement may be used to establish the rough height, with a few inches added to account for flesh. Otherwise, stature is most commonly established using a formula based around the length of a long bone such as the humerus or femur. Human height is generally two and two thirds the length of the femur, taking into consideration slight variations due to race and sex. Stature may also be approximated by a measurement from fingertip to fingertip of outstretched arms, the length of which roughly equals the body height. Ideally the complete bone is necessary, though less accurate formulae are available for incomplete bones.
The weight of the victim is often difficult if not impossible to establish, as layers of fat leave no markings on the bones. However any clothing found worn by the victim may indicate their clothes size and so their weight. Well-developed muscles will leave clear markers on the bones around the muscles. The more they are used, the rougher the bone’s surface becomes to anchor the tendons of the muscle in use. The estimated state of certain muscles may also provide clues as to the victim’s occupation, hobbies, and even handedness. For example, a tennis player will have particularly well-developed muscles throughout the arm. Similarly, playing certain instruments may leave tell-tale marks on the teeth.
Medical records can prove highly beneficial in identifying the victim. Certain diseases, previous injuries, and birth defects can all leave marks on the bones. These indicators can be studied and compared to the medical and dental records of missing people, potentially identifying them through distinguishing bone markers. Bodily implants, such as artificial hips and breast implants, often hold a unique serial number that can be used to identify the victim.
If a forensic anthropologist has been called upon, the remains are most likely skeletonised, meaning bodily tissues have decayed. In these situations, it is highly unlikely that nuclear DNA can be extracted. However it may be possible that mitochondrial DNA can be utilised to create a DNA profile. Mitochondrial DNA, or mtDNA, is transmitted through the maternal line, meaning an individual’s mitochondrial DNA originated from their mother. Though not as valuable, mtDNA is much more resilient, and can sometimes be extracted from severely decayed corpses. Visit the DNA page to find out more about nuclear and mitochondrial DNA profiling.
Aside from establishing the identity of the victim, a major duty of the forensic anthropologist is the estimation of time since death. The condition of the bones and the amount of flesh remaining, which are dependent on the likes of time, exposure, and temperature, can be studied to help determine this.
The stages of decomposition can be defined as the fresh stage, the putrefaction stage, the black putrefaction stage, the butyric fermentation stage, and finally the dry stage. The fresh stage of decomposition lasts for about three days after death. Digestive enzymes in the body begin to break down cell membranes and digest their contents, a process known as autolysis. Pallor mortis occurs, in which the skin takes on a pale colour, and signs of livor mortis may also be seen, where blood drops to the lowest points of the body. A few hours later rigor mortis sets in, in which muscle fibres begin to bind together and stiffen. Putrefaction lasts between days 4 and 10 approximately. In this stage, anaerobic metabolism of the soft tissues by bacteria and other microorganisms continues. These processes result in gas production within the body, causing it to bloat and emit strong odours. In black putrefaction, occurring between days 10 and 25 after death, the bloating of the corpse subsides, the skin blackens and peels back, and various gas and fluids are produced. The fourth stage of decomposition, butyric fermentation, occurs around 20-25 days after death. The fluids within and around the body begin to dry up, and a distinct smell is produced from the butyric acid. The remaining soft tissue is eaten by the continuing waves of insects. The final dry decay stage begins between days 25 and 50 but can last up to a year. Now all that remains are bones, hair and dry skin, which are fed on by remaining bacteria and mites.
Depending on the environmental conditions, there may be a number of occurrences. A cold, humid environment with little or no oxygen may bring about the formation of adipocere. Also known as grave wax, this is formed from the transformation of fats, and appears as a crumbly, waxy substance composed of primarily saturated fatty acids. The formation of adipocere is not particularly useful in estimating the post-mortem interval, as the speed of the process is very dependent on temperature. Alternatively, if the body is exposed to heat and dehydration or freezing temperatures and dehydration, mummification can occur. In these conditions, tissues dehydrate rapidly and the effects of decomposition are slowed down. This results in the skin of the body taking on a shrunken, darkened appearance with a vast decrease in body weight and well-preserved teeth and nails.
Insects play a great role in the decomposition of a body, therefore the rate of decomposition may be affected if the body is buried. However micro-organisms in the soil will still reach the cadaver freely. The acidity of the soil itself also affects decomposition, speeding up the process if acidity levels are high. More can be read on the role of insects in decomposition on the Forensic Entomology page. A body left on the surface will attract the attention of insects almost immediately, the various waves of insect species aiding decomposition in their own way. Within 2 weeks the remains will often be partially skeletonised, a state in which most soft tissues is gone but cartilage and ligaments remains between the bones. Within about 8 months, the remains will usually be completely skeletonised, unless if the body is buried, in which case complete skeletonisation can take between 1 and 2 years. In a hot, desert environment, the corpse can be reduced to bones in as little as a week.
Skeletal remains may be subjected to scattering by animals, often making their complete discovery difficult if not impossible. Scavengers may also damage bones, leaving gnaw marks on the bones or even completely destroying them. Remains may also be damaged or scattered by weather.
Various individual factors will also affect the rate of decomposition, and should always be taken into account when estimating time since death. Sex is one determining factor, with females generally losing one pound of tissue per day throughout decomposition, and males losing around three pounds.
If remains are completely skeletonised, determining time since death based on the bones may be extremely difficult. The presence of clothes or artefacts at the scene can help pinpoint the rough time period from which the remains originated. Any clothing remaining on or around the remains is particularly useful for this. With especially older remains, it must be considered that the bones may be historic or pre-historic, in which case they will be of little relevance to legal investigations. The presence of artefacts such as arrow heads, tools and pottery can indicate such aged remains.
Injuries & Cause of Death
With little or no flesh remaining, it may be the duty of the forensic anthropologist to seek out clues as to how the victim died and what injuries they received. Whereas in many cases it may be impossible to tell, some injuries do leave tell-tale signs on the bones.
Sharp blades such as knives, if plunged into the body deeply enough, will often leave nicks and grooves on the surfaces of any bones they come into contact with. When the blade meets the solid structure of the bone, it is also possible that fragments of the blade are broken and left behind with the remains, ideal for later comparison to weapons. Such discovered fragments may be matched directly to the weapon used, or they may at least give some indication as to the type of weapon.
A bullet may leave numerous markings on bones. If the bullet passed straight through bone, distinct holes could be observed. Such a projectile also has the potential to completely shatter a bone, or at least leave noticeable scratches across the surface. It is possible that bullets may have been left behind in the remains, stuck in one of the bones or caught up in leftover tissues.
The hyoid bone is a small, U-shaped feature in the centre of the throat. If this bone is found broken, it is likely that strangulation has occurred, though it cannot be positively determined at this point that this was the cause of death.
It is possible that not all injuries visible were received during the fatal incident, but these older wounds should still be examined closely. Fractures and similar injuries showing signs of healing may not be relevant to the current investigation, however they could be signs of previous assault, so should be taken into account nonetheless. Even fractures suffered a long time ago will be visible, potentially signifying injuries obtained during childhood. Periods of illness or malnutrition may also leave behind signs on the bones. During these periods, bone formation occurs at a slower rate between the end of the bone and its shaft. Once normal growth commences, a slight line is left behind in the bone, known as a Harris line, which can be visualised using x-ray techniques. By studying charts of known bone growth, it is even possible to establish roughly at what age this period occurred.
Forceful blows to the skull will often leave obvious fractures or even holes, the study of which can even aid in the identification of the murder weapon, more so if a narrower, sharper weapon was used. The use of a larger, blunt object produces wounds described as blunt force trauma. Blunt force trauma may leave a pattern of radiating fractures around the point of impact, the extent of these fractures indicating the force of the blow. If there are multiple blows to the skull, any radiating fracture lines from following strikes will stop at existing fracture lines. The study of these can determine the order in which the injuries were received. The skull itself is composed of a spongy layer of bone sandwiched between two harder bone layers. The inner side of the skull is cushioned by the outer and middle layers, thus is can be assumed that great force was employed if all three layers are shattered.
Forensic facial reconstruction is the method of reconstructing the living face of an individual from skeletal remains to aid identification. Initially, the skull is cleaned of any remaining tissue in preparation for the reconstruction. A number of round, rubber markers are placed at specific points on the skull. These landmarks are used to indicate the depth of flesh in these locations, their depth being dependent on the likes of sex, age, race, and the presumed weight of the individual. Strips of clay join these landmarks, with more clay applied in between to act as the ‘flesh’ of the face. Facial muscles are laid over the flesh, their structures and sizes based on the shape and size of particular facial bones. External features are then added, such as eyes, ears and a nose. Finally, the skin is coloured and an appropriate hair colour and style selected. Many of these external features are the most distinguishing points of a person’s face, but are unfortunately difficult or impossible to predict. Certain rules are relied on during the reconstruction of the face to ensure these features are as accurate as possible. The width of the nose tends to be the same as the distance between the inner corners of the eyes. The lengths of the ears are generally a similar length to the nose, and the mouth lies below the inner borders of the irises.
The result is essentially a clay model depicting the likely appearance of the unidentified individual. Though this may not be used as a sole identifier, the image may be distributed amongst the public, hopefully prompting people to come forward and make a positive identification.
Computerised 3D Facial Mapping
In more recent years, computer technology has been utilised in facial reconstruction, which can allow for the better manipulation of the image and easy transfer between computers. The skull is rotated whilst a laser scanner is used to produce a 3D image of the skull. Previously-obtained computed tomography scans of actual living people are used to determine the muscle, fat and skin to be placed over the skull, the profiles used selected based on their similarity to the victim. These methods are often preferred as they are non-destructive to the skull, so if errors are made, the process can be repeated without altering the evidence.
Education & Careers
The possible career paths within forensic anthropology are varied, some requiring merely a bachelor’s degree, whereas others demand further qualifications and training. Full-time positions in forensic anthropology are extremely rare and require extensive training, experience and education. Those who do hold such positions are most likely employed by the military or government. The vast array of training required includes an expertise in human osteology, histology, odontology, and forensics. Many experts in the field primarily work within museums or lecturing at universities, taking on legal cases occasionally.
In the US, some forensic anthropologists are certified as an expert by the American Board of Forensic Anthropology. This accreditation requires a doctorate in physical anthropology, at least three years’ experience working in the field, and passing an eight-hour written and practical exam.