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THE ANTHROPOLOGICAL USES OF THE MANDIBLE TO DETERMINE GENDER AND RACE.
Often when skeletal remains are found and confirmed as being of human origin, the determination of its gender and race, before the identification of the person is finally concluded. The mandible can therefore be used in order to determine these two key factors. This report aims to analyse the use of the mandible for sexing and ancestry (racial background), and exploring the advantages and disadvantages of this particular method, especially in terms of identifying in a diverse society.
Anthropology as defined by The University of Dundee (no date) is the "analysis of human remains for medico-legal purposes", and in the forensic aspect serves as one of the most important tools of identification of ancient and decomposed remains.
According to Rai et al (2007), one of the main differences of the genetic male and female is the individual characteristic of their skeleton. The skeleton is referred to as an excellent material in living and non-living population for genetic, anthropological, odontology and forensic investigations.
Older methods (still used today), make use of other bones of the body in order to identify the sex and race of the skeleton, these include, the cranium and the pelvis (ventral arc, subpubic concavity, and subpubic angle). Prompting Oettle et al (2009) to suggest that, physical anthropologists have persistently looked for new means of determining gender from other areas of the skeletal remains (In cases where the pelvis and upper cranium cannot be found or used for identification). According to Hu et al (2006), "the mandible is the largest and hardest facial bone and retains its shape better than other bones in the forensic and physical anthropologic field". This is of particular importance in relation to human identification as its durability can be the only reason a skeletal remains true identity is known. This quality can be exploited to distinguish ancestry and to identify gender.
The identification of skeletal remains as male or female is particularly important as it can help confirm or exclude an individual's identity. As Kemkes-Grotternthaler (2002) identifies, this determination of gender can be conducted using two methods, metrically (using previous statistics) or descriptively (Morphologically). As the cranial features vary between the two genders, and the differentiation is usually based on the features that are typically more prominent and well defined in the males as compared to those found in the females (Rai et al, 2007). It is possible to exploit this differentiation for the purposes of identification.
Vodanovic et al (2006) suggests along with others that the mandible of the male is more robust and defined, in other terms chiselled, than that of the female (as illustrated in figure 3). In a Brazilian study conducted by Suazo et al (2009), they noted that the mandible of a female (especially in children) appears filed, smooth to the touch and look and had an overall general small dimensions when measured. Franklin et al (2007), Johnson et al (1990) and Naccarato & John (2008) all noted that the dimensions of the male mandible is considerably larger and longer especially in the length and height of the mandible body. In addition, male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles as illustrated in Figure 4.
As useful as this type of method can be, to the untrained eye, the difference is not as easy to spot by simply having a look, as Taylor et al (1984) noted, the details of the mandible are often minuscule and differ in depending on the population. Therefore, the discrimination function analysis is adjusted depending on the location and origin of the remains. For example, when dealing with remains found in Africa the equation used for gender calculations will differ from those used for remains found in the Asian community. Therefore, as many human features differ extensively within any population, it is more difficult (often impossible) to identify the sex from a mandible without prior knowledge of the population from which it originated (Franklin et al, 2007).
As previously mentioned the mandible can also be used to determine race and ancestry, in order to identify which racial group the remains originate from. Because of the continental differences in our appearance due to genetics and ancestry, our skeletal frame also differs, and in this case, the mandible is unique to each racial group (Pickering, 2005). Byers (2008) noted that the Asian population have a more "vertically orientated ascending ramus of the mandible", meaning that the Asian community have a rounded mandible that possess a slight upturn at the chin. Whilst the mandible of the Caucasoid is more pointed and narrow especially in the chin region as compared to the Negroid mandible, which is far blunter and flatter (Pickering, 2005).
Rhine (1990) recognises that although the mandible can "present useful arthroscopic characteristics for distinguishing the three main ancestral groups" there are also a number of factors that can help in the assessment of racial background or ancestry, such as using other areas of the cranium.
In addition, McCusker (2007) noted, there is retention of the metopic suture, which is a common trait in the Caucasoid population (illustrated in Figure 6). The suture is usually present in the foetus as the cranial bones are forming, but usually becomes obliterated (disappears) as the cranium fully develops in the Mongoloid and Negroid population, however, remains in the Caucasoid mandible. The presentation of this suture can also serve as confirmation of the mandible belonging to the Caucasoid family.
uck & Vidarsdottir (2004) acknowledged the importance of forensic anthropology as a form of human identification, however, they noted that techniques which are used to determine race of adult remains is less certain and accurate in children.
MEASUREMENTS FOR DETRMINATION.
Anthropologists have found that certain features are specific to individuals among a population (in gender and race). Anthropometry takes measurements of bones, in this case the mandible, and compares them to charted measurements to determine which gender or race the remains could belong to. This can be difficult to study in detail because of the natural variations that occur within a population (Balci et al, 2005). The measurements taken from the mandible are compared with reference measurements stored on the FORDISC database, a database created by Ousley & Jantz (2005). The program compares "potential profiles of data contained in the database of skeletal measurements of modern humans" with the sample, a determination is made on what the gender or ancestry could be based on the typical measurements of that particular population (Burris & Harris, 1998). At this stage, a discrimination function analysis is applied, this involves applying a reliable equation to the particular bone in question (the mandible), taking into consideration the method should be applied to identical or very similar populations (Ramsthaler et al, 2007).
According to Suazo et al (2009) to determine the gender of immature or children's skeletal remains, the hip, mandible and teeth are the most reliable and useful elements to use in order to obtain accurate results. However, Suazo observed that all these elements must be used in conjunction with each other and determination cannot be based on one factor solely. In this case, the results from the metric & morphological examination of the mandible must be regarded as an additional identification tool.
It is also important to note the limitations in identifying a skeleton as male or female using only the mandible, as it can often differ between the races. For example, the Caucasoid is perceived to have a medium mandible, whilst the Mongoliod has a robust mandible, in this case, the skeleton can be mistaken and misidentified as a male skeleton, because of it strong mandible if race is not taken into account. (McCusker, 2007). In addition, the mandible in the Negroid population is described as being gracile, which is a normally a typical feature for a female skeleton. As mentioned earlier, it is important to note these racial variations, as if they are not taken into account, it is easy to misclassify the skeletal remains as a wrong gender. Therefore Loth & Henneberg (2001) suggests, the mandible can only be used in conjunction with other anthropological features (e.g. pelvis and cranium) to fully ascertain the gender or race. However, in the cases where only the mandible is found, it can be used to indicate the likelihood of being male or female and to which race it belongs.
In addition, it is important to consider the limitations of natural occurrences that may affect or alter correct identification using only the mandible, such as hereditary over-grown jaw (mandibular prognathism). As the medical history of the skeletal remains are often unknown, it is possible to misidentify the remains due to mandibular prognathism and even countering surgery for prominent mandible (as illustrated in figure 8) (Naccarato, 2008).
The mandible contributes immensely to the determination of sex and ancestry. Winson (2004) suggests that "direct observation of certain features help in the preliminary identification", however in order to confirm sex or race, a number of other measurements must be taken of the skull and pelvis, if available.
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