Descripción textual de los Casos de Uso de Negocio

The second phase of the analysis is concerned with creating a basic biological profile of the individual skeleton: determining sex, ancestry (if relevant to the identification of individuals for repatriation and/or judicial needs), age, and stature during life. It is not the intention to repeat what is widely understood about basic anthropological methods but to stress issues of key concern in forensic applications. It is, however, necessary to review aspects of methodology that are generally not well reviewed in standard osteological texts.

Figure 6.1 A forensic case laid out anatomically

6.2.2.1 Sex

Sex (not gender) must be assessed first, as it will prescribe the methods used for the estimation of both age and stature. When a biological anthropologist examines a skele-ton, he/she is determining the individual’s sex, not his or her gender. Sex is a biological consequence of chromosomal inheritance; gender is a social construct based on how the individual self-identified, was classified by his/her culture, and behaved during life.

While gender may be inferred from the context in which the skeleton appears (clothing, personal effects, etc.), the anthropologist needs to assess the skeleton independently of these features first to determine biological sex.

Methods for determining sex are discussed in standard texts such as White (2000), and France (1998), and critically reviewed by many others such as Mays and Cox (2000). Sex differences may be observed in the human skeleton after the onset of puberty and no attempt should be made to appraise the sex of an individual whose innominate is not fully fused at the acetabulum, nor of an individual who displays a complete lack of epiphyseal union of the long bones. DNA can be used to determine the sex of infants and juveniles. Caution must be applied when transferring anthropological techniques from one population to the next until the anthropologist becomes familiar with the normal range of variation between males and females within any given population.

In certain populations, most notably the United States, it is also possible to assess sex osteometrically from the cranium by employing a discriminant function. Several notes of caution are warranted. The features applicable to US populations may not be appropriate if applied to the remains of individuals derived from other geographic regions. For example, the crania of Japanese males are extremely gracile by American standards (Bass 1983; Sledzik and Ousley 1991) and may be classified incorrectly using US metric and visual cues. (A more reliable, if subtle, indicator in these cases is the extended suprameatal crest present in Japanese males, Bass 1983.) In another example, if the population to which an individual belongs is unknown, osteometrically based discriminant functions may classify the individual incorrectly because ancestry cannot be taken into consideration. Newer formulae (e.g. FORDISC 2.0; Ousley and Jantz 1996) calculated from cranial measurements obtained from a broad geographic sample allow one to input a single series of measurements and receive an output providing information of both sex and ancestry simultaneously. However, caution is warranted in applying this method as well; like all statistical packages, the program will always classify the data input into the categories available to it – and only into those categories known to it. It must also be noted that, as with morphological assessment, metric methods are also population specific and cannot be applied indiscriminately.

Only if the pelvis (or even a single innominate or pubic bone) and cranium are not available, should the anthropologist turn to other skeletal elements to determine sex.

While osteometric standards for many postcranial elements exist and provide a reasonable degree of accuracy (most classify an individual correctly approximately 80 per cent of the time), their reliability is less than that of the pelvis and cranium. Many of these formulae are based on measurement of bony landmarks that correlate strongly to size differences between males and females, such as femoral or humeral head diameter. They are, however, like all studies in human variation, population specific.

So the same precautions about cross-population applicability apply as regarding the non-metric observations discussed above. Sex determination should always be done

using as many features of the skeleton as possible. No single indicator is as accurate as an assessment of the whole.

6.2.2.2 Ancestry

The estimation of ancestry, or the biological and geographic origins of the individual according to their genetic history is an integral part of the biological profile. While most medico-legal agencies ask for a determination of the race of the individual remains in order to search missing persons files, it is not possible to precisely correlate social race and biogeographic ancestry. The former is primarily based on external differences perceived to exist among populations or ethnic groups (and definitions may differ greatly from country to country) as well as individual self-identification during life. The latter is based on population biological variability as maintained via genetic drift and marriage patterns and preferences (non-random mating). Human variation results from relative genetic isolation (endogamy) of populations for long periods of time, which accentuated particular characteristics in each population. While some variability is adaptively based, much of it is simply the result of the perpetuation of particular morphology due to breeding within a restricted area. This is all relative, as people living in the centre of a population area will most resemble the ‘norm’ for that population, while people on the edges of the population will share characteristics and ‘blend’ with those of other adjacent populations. Because more variation exists within some populations than exists between them, race as a biological concept is untenable.

The ability of most forensic anthropologists in the USA to estimate ancestry so that it does, in fact, correspond with a social race category is no mystery (Sauer 1992). Most of the formulae and morphological criteria for separating ‘whites’ from ‘blacks’ were established based on collections of individuals of known ‘race’ who had donated their bodies to science, such as those that make up the Terry Collection at the National Museum of Natural History at the Smithsonian Institution. In other words, the individual cadavers were assessed for sex and race while they were still fleshed by an anthropologist who assigned a social race category to them. Then, when anthropologists later measured the remains in these collections to derive formulae for estimating race, their race categories were those designated by someone who had already established their ‘social’ race based on their external appearance. It is no wonder, then, that these skeletally based estimates often appear to coincide with socially prescribed categories that are, however, biologically meaningless.

An anthropologist is able, nonetheless, to be fairly accurate in estimating the ancestry of individuals. Ancestry is most accurately assessed through the observation of morpho-logical and osteometric craniofacial variation (see, for example, Gill 1998; Howells 1973, 1989). Because, however, the majority of forensically-oriented craniofacial studies have been based on skeletons of known social race categories, our applied categories of ancestry are themselves rather limited (for example, African, European, Native American, and Asian). Few crania are likely to exhibit all the characteristics typical of a given population; the anthropologist makes these determinations based on the presence of a majority of characteristics that typify a particular ancestral population.

In the event that character states are truly mixed, the anthropologist should indicate that the ancestry of the individual is mixed. A cranium that displays an equivalence of European and Native American features should simply be reported as such, with no

concession to a social race category as this can be very misleading. For example, the skeleton of a young woman whose cranium displayed such a mix of features was examined; when identified, it became known that her father was ‘white’ but her mother was a Blackfoot Indian. In another incident, the cranium of a young male displayed a similar suite of features; when identified, the individual was a migrant farm worker of Mexican ancestry. His social race category would have been ‘Hispanic’ or ‘Latino,’

but such a category is really a linguistic grouping fraught with implications that have no biological population basis.

A word of further caution is appropriate here. In many international investigations of human rights abuses, ethnic cleansing and genocide, the assessment of ancestry can be highly inflammatory. These situations are created when one group of people accentuate the differences (religious, ethnic, cultural, historical, visual, etc.) between themselves and another group. While this process may be initiated by political leaders with a nationalistic agenda, the idea quickly spreads via propaganda throughout the population at large. The consequences are readily apparent throughout the twentieth century – the (alleged) Armenian genocide, the Holocaust, the Rwandan genocide, the war in the former Yugoslavia, etc. Therefore, it is necessary for the anthropologist to consider whether assessment of ancestry is truly necessary to either the identifica-tion process or the judicial process. If it is not, it is recommended that ancestry assessment should not be undertaken The potential ability of a ‘scientist’ to differentiate individuals on the basis of their cranial shape may be adding fuel to the fire by appearing to legitimize the very practices the consequences of which they are investigating.

6.2.2.3 Age at death

Estimating the age at death from the human skeleton is arguably the most important and the most difficult portion of the analysis (for a critical review of this subject, see Cox 2000). The importance of age estimation is that it allows the investigator to narrow the search through missing person’s records (for all females, for example) to a specific range (e.g. females between the ages of 25 and 35 years). Despite the methodological problems inherent with available techniques, the anthropologist must always provide a range of age, as none of the techniques for estimation can account for variation in growth and degenerative changes across sex and population differences (see, for example, Brkic et al. 2000; Simmons et al. 1999). With experience, an anthropologist will be able to provide an age range estimate with reasonable accuracy, but not with precision (he or she will never report that ‘the individual was 22 years of age’ but rather that ‘the individual was 20–25 years of age’). The anthropologist should always examine all available skeletal markers of age, and not rely on a single age indicator. The final age estimate must be broad and inclusive; it should incorporate the age ranges for all indicators. For example: the epiphyseal age for a skeleton is  17 and  30 years;

the pubic symphysis provides a range of 19–34 years; the auricular surface of the ilium suggests 20–24 years; and the sternal rib morphology indicates 24–28 years (see Figure 6.2). An age estimate of 20–30 years might be rather broad, but not inap-propriate. Margins of error should always be stated. It should be remembered that most ageing methods (juvenile and adult) available to anthropologists are also population specific and they may only be applied to other populations with caution. In juveniles, nutrition, disease, altitude, and other environmental factors have been demonstrated

to affect both growth and maturation should be regarded as the more reli-able age indicator. If the individual suffered from nutritional stress or disease, it is not unusual for skeletal growth to be retarded by several months or years relative to dental maturation. Dental development in sub-adults is the most important means of age estimation. Both the deciduous and permanent dentition develop through well-defined stages of formation and eruption (Garn et al. 1959). The best means of evaluating dental age is radiographic, although a visual inspection is sometimes adequate for a rough estimate. Standards for dental eruption exist for several populations, but the variability should not be underestimated. It should be remembered that the sequence of development and eruption may be regarded as more fixed than the timing of eruption.

6.2.2.4 Stature

If the remains contain any complete long bones, stature estimation can be accomplished for USA and some other populations with both ease and accuracy. It must be remem-bered, however, that as discussed above for other aspects of the biological profile, stature formulae are population specific to geographic area and time period. Nutrition, disease, altitude, and other environmental factors all affect both growth rate and trajectory, and hence they impact upon population target height (and average height). Most stature formulae are based on the assumption that a long bone is proportionally related to the overall stature of the individual. Stature estimation can be quite accurate (if not precise) when the individual is compared to a population with established growth curves, known average statures and stature distributions, and one which is contemporary with the individual. This is particularly important since secular trends regarding proportionality and stature estimation factor into the accuracy of prediction. Jantz and Meadows (1995) and Simmons et al. (1990) both discuss the secular trends in femur : tibia ratio over time in the USA, based on data from the Terry and UT-K collections. Tibia length is seen to have increased over the past 50–60 years, and now accounts, proportionally, more for total stature than does femur length. Similar trends have been observed in stature and body proportions among the Japanese (Ohyama et al. 1987) and in other populations. Obviously, this renders the accuracy of stature estimates for recent leg bones, when using the Trotter and Gleser (1952) formulae, subject to question. If an individual in the USA died prior to the 1960s, for example, the Trotter and Gleser formulae are probably the appropriate ones to use; if on the other hand, the individual died within the past 20 years, then Ousley’s (1995) equations based on a modern Figure 6.2 The right fourth sternal rib used to

estimate age in a forensic case

forensic sample are probably better. Certainly the original observer’s measurements must be accurate and replicable for any stature estimation method to be reliable. Jantz et al. (1994) recently pointed out discrepancies in Trotter’s measurements of the tibia as used in her 1952 and 1958 formulae (Trotter and Glaser 1958). These articles recom-mend that if the 1952 formulae is used, the maximum tibial length without the malleolus should be measured, if the 1958 formulae is used, the maximum tibial length including the malleolus should be measured. Furthermore, they recommend that the 1958 formulae be avoided, as Trotter’s original measurements cannot be assessed for accuracy.

Estimating stature from fragmentary long bones (i.e. Steele 1970) presents some unique problems concerning the ability to replicate measurements. The Steele formulae covered all long bones, but the landmarks were particularly difficult to locate, and hence measurement reliability and repeatability were compromised. Simmons et al. (1990) attempted a revision of the Steele method (for the femur only) by proposing more clearly defined skeletal landmarks. Their results actually bettered Steele’s, albeit to a small degree, but still require the estimation of bone length first, prior to the estimation of stature. This compounds measurement error, as two formulae are used, both with standard errors of estimated. With both the Steele and Simmons, et al. formulae, however, the estimates are quite broad, and may serve as exclusionary evidence but only for professional basketball players and jockeys!

As in estimating age, it is vital to provide a stature range, not a precise estimate of an individual’s height. Some individuals (e.g. Ousley 1995) advocate using two standard deviations for estimating stature, thus insuring that the individual’s height in life will fall within the low and high ends of the range. While this may be the statistically correct procedure, most stature estimates using one standard deviation usually estimate an individual’s height with excellent results. It should also be noted that while stature estimation is a necessary portion of the biological profile of an individual, and is often useful in single case-work in the USA, it is not a particularly dependable criterion for identification in an international setting (Komar 2003). In the USA the stature estimate may help to eliminate a range of missing persons (e.g. those under 170cm and over 180cm in height) from the pool of possible victims. However, in places such as Rwanda or Bosnia where ante-mortem stature measurements are not routinely recorded (e.g. no medical or driver’s license statures available), the information is of equivocal value. Relatives may be able to estimate the stature of a missing person, but as yet no standards exist for correlating ‘recollected stature’ with estimated skeletal stature. In addition, applying any stature formulae consistently to the Srebrenica population revealed that the vast majority of the 4,500 individuals exhumed were of similar stature, between 170–180cm.