Metric analysis of sex differences in South African black and white pelves

Sex determination of unknown skeletal material is one of the most vital determinations made by forensic anthropologists. Numerous studies have focussed on the differences, both osteometric and morphological, between the sexes of a particular racial phenotype and population. Previous work by a variety of researchers has underscored the necessity of population specific standards. The purpose of this research is to metrically assess sex differences in the pelvis of South African whites and blacks and develop standards tailored to these groups. Data were collected from 400 known sex/race skeletons from the Pretoria and Dart Collections. Nine measurements (traditional and newly developed) were taken and subjected to SPSS stepwise and direct discriminant analysis. Results indicated that there are significant differences (p < or = 0.001) between the sexes of both races for most measurements. Discriminant function analysis selected ischial length as the most sexually dimorphic dimension in whites (averaged 86% accuracy), while acetabulum diameter was most diagnostic in blacks (averaged 84% accuracy). Six functions were developed from the pelvic dimensions. Highest accuracy was achieved from Function 1 (including all dimensions) which averaged 95.5% correct classification in whites and 94% in blacks. Functions based on selected parts of the pelvis were not as effective and ranged from 73-86% in whites and 72-84% in blacks. This research provided evidence of the significant sex differences that exist between the pelves of South African whites and blacks whilst measurements used here for discriminant function analysis gave classifications with high accuracies. These results can be used to aid in the identification of human skeletal remains in South Africa.

Sexually dimorphic pelvic morphology in South African whites and blacks

It is well known that there is metric and morphologic variation in the expression of sexual dimorphism between racial phenotypes and populations. Therefore, the purpose of this research is to assess morphologic sex differences in the pelves of South African whites and blacks. Results will be used to improve the identification of human skeletal remains by producing group specific standards. Morphologic features of both left and right os coxae were studied in a sample of 400 known sex/race individuals from the Pretoria and Dart collections. Bones that were clearly pathologic or visibly deformed were excluded from the study. Data were subjected to SPSS analysis. Results indicated that overall, public bone shape was the easiest to assess and was the most consistently reliable morphological indicator of sex in both sexes and population groups. At 88% average accuracy, the most discriminating traits in whites were pubic bone shape and subpubic concavity form. In blacks, greater sciatic notch form allowed the highest separation, averaging 87.5%, followed by pubic shape at 84.5%. Important findings included the fact that there were significant differences in the accuracy of sex determination from pelvic morphology between both males and females and whites and blacks. In conclusion, this study provides quantification of individual morphological traits in the os coxae of white and black South Africans that will be of value in forensic and archaeological analyses, especially when dealing with fragmentary remains. It also demonstrates that population differences affect the expression of sexual dimorphism and must be accounted for to develop the most effective methods of analysis.

Metric assessment of race from the pelvis in South Africans

It is well known that there are measurable differences between whites and blacks in the size and proportions of skeletal components. There are also metric differences among populations within these racial phenotypes. The population specific quantification of this variation can be used to aid in the identification of racial affinity in the absence of a more racially definitive skeletal element like the skull. Therefore, the purpose of this research is to quantify these differences in the pelvis of South African whites and blacks. A sample of 400, ostensibly healthy known sex/race os coxae was examined. Skeletal material was obtained from the Pretoria and Dart collections. A series of 13 measurements were taken Data were subjected to SPSS stepwise and direct discriminant function analysis. Pubic length was chosen as best for discriminating between races for males and iliac breadth as best in females. Highest average accuracies (Function 1) were 88% for males (pubic length, greater sciatic notch posterior width, acetabulum diameter, total height) and 85% for females (pubic length, greater sciatic notch posterior width, acetabulum diameter, iliac breath). In conclusion, this research resulted in the development of standards of identification tailored to this population and unquestionably demonstrates that race differences in the skeleton are highly significant and must be considered in all skeletal analyses.

Sexually dimorphic mandibular morphology in the first few years of life

Sex differences in the youngest skeletons are very subtle, and any method that can separate males and females significantly better than chance will be of value. Compounding the problem is a paucity of immature skeletons of documented age and sex. In 1992, S.R.L. examined 62 juvenile mandibles of white and black South Africans of known age and sex (from birth to 19 years) from the Dart Collection to determine if the sexes could be differentiated by morphologic traits. By age 6 years, adult chin shapes were already recognizable. Prior to that age, differences were observed in the shape of the inferior border of the symphysis and outline of the body. The male chin base extends steeply downward relative to the adjacent body, coming to a point or squaring off at the symphysis. In females, the symphysis descends gradually to a more rounded base, and even when pointed, the transition is not abrupt. On the outer border of the corpus, the sides diverge sharply to form a \_/ shape from a roughly horizontal anterior region in males, while the female contour is rounded, reflecting the smoothly curved transition from front to sides. These traits were manifest from the eruption of the central incisors until about 4 years of age. The features were tested on all 19 Dart Collection mandibles in that age range. Average accuracy for three different testers was 81%, and males were consistently identified more accurately than females. This new method was then tested on a known sex sample of 11 individuals from 0 to 7 years of age. These included CT scans of 9 French children and the remains of 2 South African black forensic cases. Sexing accuracy was 82% (9/11). The only two missexed cases were both female and over age 6 years. In conclusion, the results of this study indicate that it is possible to determine the sex of very young mandibles. The new sexually dimorphic morphologic configurations introduced here have demonstrated repeatable discrimination with the highest level of accuracy (81%) reported and tested for this age group. Preliminary research indicates that both the male and female shapes are clearly recognizable in archaeologic and premodern hominids as well as chimpanzees.

Sexual dimorphism in the humerus: a comparative analysis of Chinese, Japanese and Thais

Determination of sex from the skeleton is vital to medicolegal investigations. There is no longer any question that populations differ in size and proportions and these differences affect the metric assessment of sex. The extent of variation in sexual dimorphism among Asian Mongoloids within and between regions has not been quantified by discriminant function analysis, nor have standards for most groups been introduced for the humerus. Therefore, the purpose of this research is to establish metric standards for sex determination from the humerus of Chinese, Japanese and Thais, as well as to compare size and sexual dimorphism in these Asian Mongoloid populations. The database for this study consisted of documented skeletal samples from China (N = 87), Japan (N = 90), and Thailand (N = 104). Six standard dimensions, including maximum length, vertical head diameter, minimum midshaft diameter, maximum midshaft diameter, midshaft circumference, and epicondylar breadth were taken and subjected to stepwise and direct discriminant function analysis. Of dimensions selected by the stepwise function, vertical head diameter and epicondylar breadth were the only elements common to all three groups. Overall, mean accuracies were highest using formulae produced by the stepwise procedure and ranged from 86.8% in the Chinese to 92.4% in the Japanese to 97.1% in the Thais. Group comparisons also revealed that while the Chinese had the largest measurements, they were the least dimorphic. The reverse was true for the Thais and the Japanese were intermediate on both counts. In cross validation tests, classification accuracy decreased in all cases where a formula from one group was applied to another. It was therefore concluded even though all individuals were Asian Mongoloids, these regionally diverse populations exhibited significant metric differences that affect sex determination from the skeleton. These findings confirm those of previous studies that there is a need for group specific metric standards of assessment.

Metric and comparative analysis of sexual dimorphism in the Thai femur

Identification of sex from the skeleton is an important demographic assessment in medicolegal investigations. Studies have demonstrated that populations differ from each other in size and proportions and that these differences can affect the metric assessment of sex. It is therefore vital to determine if population differences are great enough to necessitate group-specific standards. To date, there have been no attempts to create standards of assessment for modern Thais. Therefore the purpose of this research is to establish standards from which to determine sex from the femur using a new skeletal collection housed at the Chiang Mai University Department of Anatomy. The sample is composed of 104 individuals (70 males, 34 females). Six standard osteometric dimensions including maximum length, maximum head diameter, midshaft circumference, midshaft anterior-posterior and transverse diameters, and bicondylar breadth were measured and analyzed by stepwise discriminant function statistics. To understand population differences, formulas derived from Chinese, South African whites and American whites and blacks using the same method and variables were tested on the Thai sample. Results indicated that maximum head diameter and bicondylar breadth are the optimal combination for sex diagnosis and yielded 94.2% accuracy. Direct analysis using predetermined single or multiple variables also revealed bicondylar breadth as the best single dimension (93.3%). In cross-tests on the Thais, the Chinese formula gave the most favorable outcome with unsatisfactory results for all other groups. The present research confirms that sexual dimorphism is better reflected in breadth dimensions than in bone length. Comparisons showed that Thais are very different metrically from whites and blacks, and although they most resemble the Chinese, these two groups are not identical. These findings underscore the need for population-specific formulas for identification of sex from the skeleton.

Mandibular ramus flexure: a new morphologic indicator of sexual dimorphism in the human skeleton

In the skeleton, male and female characteristics lie along a continuum of morphologic configurations and metric values. Size alone is not the best indicator of sex. In contrast, morphologic differences that arise from genetically sex-linked growth and development allow better separation of the sexes. This study presents a new morphologic indicator of sexual dimorphism in the human mandible. A sample of 300 mandibles from adults of known sex primarily from the Dart collection was analyzed. Of these, 100 were found to have obvious bony pathologies and/or excessive tooth loss ("pathologic" sample). Thus, the normative sample consisted of 200 individuals (116 males, 84 females). Examination of morphologic features led to the discovery of a distinct angulation of the posterior border of the mandibular ramus at the level of the occlusal surface of the molars in adult males. Flexure appears to be a male developmental trait because it is only manifest consistently after adolescence. In most females, the posterior border of the ramus retained the straight juvenile shape. If flexure was noted, it was found to occur either at a higher point near the neck of the condyle or lower in association with gonial prominence or eversion. In the normative sample, overall prediction accuracy from ramus shape was 99%. When the "pathologic" sample was analyzed separately, 91.0% were correctly diagnosed. Because the African samples were overwhelmingly black, this trait was also tested on American samples (N = 247) of whites (N = 85), Amerinds (N = 66), and blacks (N = 96) that included a mix of healthy individuals and those with extensive tooth loss and evidence of pathology. The results were nearly identical to those of the "pathologic" African sample, with accuracies ranging from about 91% in whites and blacks to over 92% in Amerinds. Total accuracy for all African and American samples combined (N = 547) is 94.2%. In conclusion, at 99%, sexing from the shape of the ramus of a healthy mandible is on a par with accuracy attainable from a complete pelvis. Moreover, there is no record that any other single morphologic or metric indicator of sex (that has been quantified from the adult skeleton) surpasses the overall accuracy attained from the more representative mixed sample produced by combining all groups assessed in this study. The usefulness of this trait is enhanced by the survivability of the mandible and the fact that preliminary investigations show that the trait is clearly evident in fossil hominids.

Estimation of age at death using cortical histomorphometry of the sternal end of the fourth rib

Given the often fragmentary nature of unidentified human remains, and the importance of using multiple criteria to estimate age at death, it is essential to have a variety of methods that use different anatomical sampling sites. In this study, osteon population densities (OPDs) were determined from transverse sections removed from an area immediately adjacent to the sternal ends of 60 autopsy rib samples. Regression analysis was performed using age at death as the dependent variable and OPD as the independent variable. The results of a "training set/test set" strategy to evaluate the performance of the histological age predicting model indicates that it provides reasonably reliable and accurate age estimates. A multiple regression model using both OPD and the mean age for a rib's morphological age according to the phase method of Işcan et al. [7,8] is also presented. This later age predicting model is recommended when both methods are applicable.

Intercostal variation at the sternal end of the rib

The human rib has proven to be an important site for the assessment of age at death in the adult skeleton. The rib phase method, featuring race and sex specific standards developed by two of the authors (Işcan and Loth), is proving successful in paleodemography and forensic anthropology. However, as the authors pointed out in earlier publications, it is not always possible to isolate the fourth rib upon which the standards are based. This can be a factor because although a certain degree of intercostal variation does exist, its extent has not been quantified in a modern forensic population. Therefore the purpose of this paper is to determine if standards from the fourth rib can be used for adjacent ribs 3 and 5. Ribs 3, 4, and 5 were collected at autopsy from recent medical examiner's cases of known age, sex and race. The sample consists of 135 white males and females of age range 3-99 years. Each rib was assigned to an age phase using the established standards. The results of this analysis indicated that > 79% of cases, all three ribs fell into the same phase, and intercostal differences were within one phase for 98% of the sample. It may thus be concluded that age can also be assessed from these adjacent ribs using the present standards.

Racial variation in the sternal extremity of the rib and its effect on age determination

Most research on the aging process in the skeleton has not considered or elaborated differences that may exist between the races. Thus, techniques developed for the estimation of age assume that the racial background of the standards is compatible with the specimens to be assessed. However, racial differences in areas such as skeletal growth and bone density have been reported, along with specific variations in the aging process, in the ribs of disparate populations. The present investigation examines metamorphosis in the sternal ribs of American blacks (N = 53 males, N = 20 females), and tests the application of age estimation standards developed by the authors from a white population. All specimens were obtained from medical examiner's cases of known age, sex, and race. Although the sample was limited in both quantity and age range, analysis of the data revealed racial differences in both rate and pattern of metamorphosis. Statistical analysis showed that the calculated mean age per phase for black ribs was nearly identical to whites in Phases 1 through 4 or until the mean age of 28 years. By the early 30s, differences in morphology and their chronological association with the aging process became apparent and increased with age in both sexes. Blacks were consistently overaged from 3 to 10 years in Phases 5 through 7. Therefore, it was concluded that biological differences between these populations do exist and can affect age estimation from the rib. Social factors may also be involved, but they cannot be demonstrated from the available data. While the degree of interracial variation does not require completely new standards, the authors have suggested specific modifications of the white standards for use on black specimens.

Determination of age from the sternal rib in white females: a test of the phase method

Sex differences in both the rate and pattern of aging in the sternal extremity of the rib necessitated the development of separate standards of age determination for males and females. A test of the male phase technique has already demonstrated its reliability and soundness. The present study was carried out to evaluate the female phase standards. A sample of 10 test ribs including 2 control specimens, was judged by 28 volunteers representing several levels of education and experience in the forensic and anthropological sciences. As in the male test, the judges were asked to assign each unknown rib to an age phase by comparing it with photographs of prototype specimens from the original study. Analysis of the results revealed minimal interobserver error between the doctoral and predoctoral groups, and no discernible association between morphological variation in the rib and antemortem history. Furthermore, rib assignment for both groups of judges averaged well within 1 phase of the ideal phase in which the specimen would have been placed based solely on chronological age.

Determination of age from the sternal rib in white males: a test of the phase method

The effectiveness of a given age determination technique can better be assessed by testing the standards on unknown specimens. A test of this nature was carried out to evaluate the authors' previously published phase method for age estimation from the sternal extremity of the rib. A sample of 15 test ribs was judged by 25 physical and forensic anthropologists with varying levels of education and experience. The judges were asked to match the rib to the phase it most closely resembled by comparing it with the photographs from the original study. The results indicated that interobserver error based on experience was minimal, and nearly all of the participants averaged within one phase of the ideal. Variation appeared to be greater among the ribs than among the judges, yet no consistent association could be made between this variation and factors such as cause of death, antemortem medical history, drug or alcohol abuse, and occupation.

Age estimation from the rib by phase analysis: white females

Metamorphosis at the sternal extremity of the rib has already been established as a reliable indicator of age at death. Using a sample of white males, it was shown that an accurate estimation of age can be made by direct examination of the bone itself. However, because of sexual differences in hormonal production and dimorphism in the skeleton, the present study was carried out to develop an appropriate standard for age determination from the sternal rib in white females. The sample consisted of 86 ribs of known age, sex, and race. Observations were made at the costochondral junction with special attention to pit formation (its shape and depth), changes in the walls and rim surrounding it, and overall bone density and texture. Based on changes in these areas, the ribs were separated into nine phases (0 through 8). The most rapid metamorphosis occurred in Phases 1 through 4 (mean ages 14-28) with changes noticeable at 3 to 4 year intervals. After mean age 28, this process slowed, considerably expanding the interval between phases to 10 to 15 years. The female ribs showed both earlier initial pit formation and a different morphologic pattern of aging as compared with males. Statistical analysis revealed that the features chosen to delineate the phases are valid predictors of age. This study has shown that the sternal rib can provide an accurate estimation of age in females spanning a mean age of 14 to 76 years.

Age estimation from the rib by phase analysis: white males

The determination of age at death is an important part of physical and forensic anthropology. Techniques now in use vary from direct observation of a bone to microscopic examination of a given segment. This study introduces the sternal end of the rib as a new site for age estimation by direct observation. The sample consisted of 118 white male ribs of verified age, sex, and race. The ribs were assigned to one of nine phases (0 through 8) based on changes noted at the costochondral junction. These included the formation of a pit, its depth and shape, configuration of the walls and rim surrounding it, and the overall texture and quality of the bone. Statistical analysis indicated that these changes were age related. It was further revealed that metamorphosis was most rapid and uniform from the mean age of 17 to 28 years (Phases 1 through 4). The rib morphology was more varied after age 39 (Phase 5) resulting in a wider range for the predicted age. Our study concluded that the sternal rib end may yield a similar degree of accuracy to the pubic symphysis and perhaps better than that for cranial sutural closure. Our technique also enables the forensic scientist to use the rib for corroboration with age estimations obtained by traditional methods.

Metamorphosis at the sternal rib end: a new method to estimate age at death in white males

While the pubic symphysis and intracortical morphometry have provided successful results in estimating age at death, other methods and sites in the skeleton are needed to improve the accuracy of age estimation. This research is an attempt to develop a new age-determination technique by using the sternal extremity of the rib. The right fourth rib was collected at autopsy from 93 white males. The sternal extremity of each rib was analyzed in relation to the pit depth (component I), pit shape (component II), and rim and wall configurations (component III), each of which was divided into six stages. Results indicated that the age at death can be estimated from a rib within about 2 years in the second decade to about 7 years in the fifth and sixth decades of life. Pit shape and rim and wall configurations yielded better results than absolute pit depth alone. While this method has a potentially important contribution to skeletal anthropology, factors such as sex differences and biomechanical variation between individuals may affect the determination of age from the rib.