Forensic anthropology refers to a specialised branch of physical anthropology particularly applied to medico-legal matters. When dealing with a set of human remains, a primary fact to ascertain is the identity of the individual and how they may have died, which is understandably not straightforward if all that remains of a body is the skeleton.
Through the study of bones, an array of information can be ascertained regarding the remains including, but by no means limited to, age, gender, ethnicity, cause of death, and even indications of lifestyle such as where a person might have lived. The adult human skeleton consists of some 206 individual bones, with there being even more in the skeleton of a child, whose bones have not undergone certain fusion processes yet, and many of these bones may prove useful to the anthropologist.
Bones develop from cells known as osteoblasts, first beginning as soft cartilage before the bone hardens through the introduction of various minerals, a process known as ossification. Bones can be divided into a number of classes; short, long, flat, sesamoid and irregular bones (Gunn, A, 2009). Short bones, such as the carpal bones within the wrist, tend to be as wide as they are long. Long bones are, as the name suggests, longer in length and also tend to be slightly curved, for example the femur. Flat bones, such as the ribs and breastbone, could be described as being fairly flat and plate-like. Sesamoid bones refer to small bones embedded in a tendon, often found in joints, such as in the knees and wrists. Finally, irregular bones refer to a certain class of bone that do not belong in the other categories, such as the bones composing the spine.
It is initially essential to establish whether recovered bones are of human or animal origin. Whereas the answer to the question may be obvious when a full set of skeletonised remains are present, a great deal more expertise is needed when only a few or even a single bone is found. The general shape, size and structure of the bones may be sufficient to determine likely species, and methods for distinguishing between human and non-human remains have also been established based on microscopic differences in bone structure (Urbanova, P et al, 2005). If the bones are relatively recent they may contain the proteins required to carry out serological tests to establish the species.
Establishing the sex of skeletonised human remains is not generally too difficult, as there are a number of morphological differences between the skeletons of males and females. If the remains have not reached the latter stages of decomposition, some indicators of sex may still be present in the softer tissues. For instance, the prostate gland in males and the uterus in females do not decay until later than other soft tissues. Should the bones be all that remains, perhaps the most significant indicator of sex is the pelvis. In a female the pelvis presents a U-shaped sub pubic arch, as oppose to the V-shape found in a male pelvis. As would be expected, the female’s pelvis is also generally more spacious to allow for childrearing, with a wider sub-pubic angle and sciatic notch. Furthermore, examination of a female’s pelvis may even indicate whether or not she has previously given birth, offering a further detail for identification purposes. Through examination of the skull it may also be possible to determine the likely sex of the remains, with the skull of a male tending to display a larger, squarer and more pronounced jaw, a more prominent supraorbital ridge (brow), and more rectangular eye sockets (orbits). Though not an infallible means of sex determination, the general size of bones can provide some indication as to whether the remains belong to a male or female. As the muscles in a male tend to be larger and better developed, the bones are generally larger and to an extent more robust than those of a female. However it should be noted that establishing sex based on the human skeleton is often challenging when dealing with the remains of pre-pubescent children, as certain indicators, such as the widening of the hips in a female, may not have occurred until puberty. Furthermore, the natural sex of an individual may not be consistent with the gender of that individual (for instance, a person designated female at birth may be living as a male), hindering the identification process.
Establishing the ethnicity of an individual is generally carried out by studying the skull, which is typically classed as belonging to a Caucasoid (or Caucasion), Negroid or Mongoloid. The cranium itself is typically long, narrow and high in Caucasians, similar in Negroids but lower, and more rounded in individuals of Mongoloid ancestry. The size of the nasal opening may be used as an indicator for ethnicity, with the nasal cavity of a Caucasian being narrower and higher in comparison to the broader opening belonging to an individual of Negroid origin, and Monogloids sitting somewhat in between. The eye orbits can also provide clues as to the possible ethnicity, with individuals of Caucasian ancestry tending to have sloped orbits, as oppose to Negroids who generally possess more rectangular eye orbits and people of Mongoloid ancestry with rounder orbits. The mastoid process, which refers to a particular part of the skull just behind the ear, tends to appear as a wider projection in Negroids whereas this is often more pointed and narrow in Caucasian individuals. The teeth may also prove beneficial to a certain extent, with individuals of a Mongoloid ethnicity tending to have upper incisors that could be described as ‘shovel-shaped’ with a curved inner surface, as oppose to the more flat surface found in the teeth of Negroids and Caucasians. An additional observation to note relating to teeth, Caucasians tend to have smaller teeth and more overcrowding, commonly resulting in impacting third molars that must be removed. However the determination of ethnicity is certainly not straightforward, with the occurrence of ‘racial hybridity’ being a problem in establishing ethnicity of an unknown individual. This is the result of breeding between different racial groups, resulting in individuals possessing features that are typical of two or more racial groups.
Once a body has decayed to such an extent that only bones remain, the estimation of age may not be as obvious as if soft tissues were present. Fortunately, there are many indicators in the skeleton that can be used to establish the likely age of the victim at the time of death. As previously mentioned, the skeleton of a younger individual is composed of significantly more than the 206 bones found in an adult. This is because as the human skeleton develops, a process known as ossification occurs in certain areas, which is essentially the fusion of bones. The appearance of certain ossification centres can estimate the age of a younger individual, though this becomes decreasingly beneficial as an individual ages. In the human skull there is a series of zigzag lines known as sutures which separate the plates of the skull. Over time these sutures harden and become less distinct. The epiphyseal fusion of bones (the fusion of the shaft of a bone to the end of the bone) can equally act as an age indicator. In addition to this, the study of tooth eruption can also be a useful indicator of the age of an individual, though from approximately the mid-twenties this is not necessarily valuable. Once an individual has reached a particular point in adulthood, generally around the mid-20s, accurately determining age becomes difficult, because tooth eruption has generally reached a stage of completion as has the fusion of bones. Depending on the age of the individual, there may be some signs of age-related conditions such as osteoporosis or arthritis, though once again there are inaccuracies to take into account as not all older people will develop these conditions and furthermore some younger people may be susceptible to them.
Age of Remains
Establishing the age of a set of remains, as in how long ago the individual died, is often a difficult task. With more recent sets of remains, there may still be some tissues present on the body to help pinpoint the age of the body. Certain soft tissues and ligaments can last for up to 5 years, so the presence of these may at least be able to narrow down time since death to the last few years.
Typically, isotope analysis can prove to be particularly beneficial in establishing the likely age of remains. Isotopes are atoms of the same element, and with the same chemical properties, but differing in the number of neutrons within the nucleus (and thus have a slightly different atomic mass). Among the most common elements to be studied in isotope analysis are carbon, nitrogen, oxygen, strontium and hydrogen. This branch of study, which can be focussed upon unstable or stable isotopes, is based on the principle that many elements within the body exist as various isotopes, many of which are taken into the body by eating, for instance. Bones and teeth are usually subjected to isotopic analysis in cases of dating skeletonised human remains, though if present hair and nails may also be used.
The isotopic analysis of stable isotopes, such as carbon-14, is beneficial in estimating time since death. Whilst an organism is living it is constantly taking in carbon, for instance through the ingestion of other organisms containing the isotope. However upon death, it ceases acquiring new 14C and so levels of 14C begin to decline. It is thus possible to establish a likely time period since death by measuring the quantities of 14C present in the remains. Despite the benefits of this technique, it is not as accurate as would be ideal, and establishing time since death using isotope analysis can only allow for an estimation. 14C dating is also only ideal for older remains (older than at least 100 years), as the technique is simply not accurate for younger remains. Due to this fact, the study of the 14C isotope is not necessarily of the greatest benefit to forensic science as other isotopes may be.
For example, the analysis of the lead-210 isotope (210Pb) is perhaps of more use to the forensic scientist due to its shorter half-life of 22.3 years. As with the 14C isotope, 210Pb is absorbed by the body through the ingestion of food and, upon death and thus the halt of food intake, the isotope will begin to decay. By measuring the amount of this isotope in a set of remains in comparison to the levels of the isotope seen in the body of a living person, it is possible to determine the likely time elapsed since death. Similarly, research is being conducted into the analysis of a polonium isotope (210Po), which has a significantly shorter half-life of only 138 days and thus has the potential to pinpoint time since death with greater accuracy.
However it must be taken into account that exposure to certain conditions can affect the isotopes present in a sample and the ratios of these isotopes. Furthermore, isotopes are ubiquitous in the environment thus it is entirely possible for detected isotopes in a sample to actually be the result of contamination.
As previously discussed, the study of isotopes making up a set of remains can be used to provide various forms of information, such as the likely age of the remains. Another particularly beneficial use of isotopic analysis is to determine the possible geographical origin of remains (known as the provenance) through the study of stable isotopes, often through the use of stable isotope ratio mass spectrometry (SIRMS). The study of various elements such as hydrogen, carbon, oxygen, nitrogen and strontium can theoretically be used to trace an individual across various locations throughout their life.
Different geographical locations are known to have different, often distinct isotope ratios. The varying isotope ratios in different areas occurs due to a process known as isotopic fractionation, in which certain isotopes become enriched over others. The elements studied in this instance exist in different isotopic forms – for instance, strontium exists as four stable isotopes; 84Sr, 86Sr, 87Sr and 88Sr. Because their ratios vary between different geographical locations, thus people and animals will ingest food and water from those locations, the ratio of isotopes measured in a sample can act as a kind of ‘fingerprint’, indicating the likely location in which a person had lived. Furthermore, because isotopes are taken into the body at different points throughout an individual’s life, isotope ratios can also infer certain changes in a person’s location throughout his or her life.
In order to estimate the height of an individual from the complete skeleton, direct measurements can be taken and thus height determination is usually relatively straight forward, provided the presence of tissue prior to decomposition is taken into account. When dealing with an incomplete skeleton or only certain individual bones, estimating the height of an individual may still be possible. By measuring the length of the long bones, ideally the femur, fibula and tibia in the leg, it is possible to estimate height based on stature tables. These tables take into account the race, sex and age of the individual along with the measurement of the long bone. Determination of an individual’s stature based on a skeleton or bones will only ever be an estimation, as it is not always possible to accurately take into account the changes soft tissue would have had on the individual’s height in life.
Injuries and Cause of Death
By X-raying skeletal remains, it may be possible to obtain information that could lead to both establishing a cause of death and even identifying an individual. There may be evidence of injuries obtained earlier in life that have left noticeable markings on the bones, for instance fractures and breakages or even the presence of artificial bones. Furthermore, there may be evidence of bone disease such as osteoporosis. Studying the teeth of the remains may provide important clues, particularly if the individual had any distinguishing dental features or dental work such as fillings carried out. All of this information may be compared to the medical records of known individuals to aid in confirming or disputing the identity of the skeletonised remains. Dental records in particular often prove beneficial in identifying an individual who cannot be identified by any other means, providing they have had dental work carried out and have some dental records stored somewhere.
Unsurprisingly, bone contains very little nuclear DNA, thus typical DNA profiling methods are not likely to be possible. However bone does contain mitochondrial DNA, which typically persists for longer than nuclear DNA. Mitochondrial DNA is solely inherited from the maternal bloodline, thus it does not contain any genetic information from the individual’s father. If mitochondrial DNA can be successfully extracted and analysed, it may be possible to compare it with living maternal relatives to aid in identification.
Provided the skull is in a reasonable state, it may be possible to reconstruct the face of an individual based on the skull by various available methods to aid investigation of an individual. The process of photosuperimposition is fairly rudimentary. A photograph of the skull is taken and a photograph of an individual in life overlaid to determine whether the features of the individual match those of the skull. This technique is not always ideal, as the photograph of the individual must be altered in size to match that of the skull, which may not always be accurately possible. A little more complex, facial reconstruction essentially involves rebuilding the likely facial features of an individual using a cast of the skull as a baseline. The technique generally utilises facial markers placed in specific locations on the skull and modelling clay, which is intricately applied to the surface of the skull to the required depths to simulate facial tissue, smoothed and coloured to resemble skin. Further additions such as the nose, ears and lips will then be constructed. Following this additional features such as prosthetic hair and eyes can be added in attempts to reconstruct the facial features of the individual. Of course when dealing with an entirely unidentified victim certain presumptions must be made, such as the colour of a person’s hair and eyes or the presence of facial hair. Even the depth of tissues on an individual’s face can only be estimated to a certain extent, as the underlying bone structure will not indicate this. The technique of facial reconstruction may also be carried out using sophisticated computer software if available. Upon completion of any forms of facial reconstruction, the image produced can be distributed as necessary to aid identification.
Please see the human decomposition page for more details.
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Gunn, A (2009). Essential Forensic Biology. Oxford: John Wiley & Sons.
Forensic Magazine. Tracing Unidentified Skeletons Using Stable Isotopes. [online][Accessed 13 Jan 2015] Available: http://www.forensicmag.com/articles/2007/01/tracing-unidentified-skeletons-using-stable-isotopes
The University of Western Ontario Journal of Anthropology. Racial Identification in the Skull and Teeth. [online][Accessed 20 Feb 2015] Available:http://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1137&context=totem
Urbanova, P et al. Distinguishing between human and non-human bones: histometric method for forensic anthropology. Anthropologie. 43(2005), pp. 77-85.