Population variation in sexual dimorphism in the human innominate

Sex assessment from the pelvis: a test of the Phenice (1969) and Klales et al. (2012) methods

Sex assessment is one of the first steps of routine forensic anthropological examinations and it provides a crucial element to identify a set of human skeletal remains. In bioarchaeological contexts, this assessment is also important, as it helps in the reconstruction of past societies. Sex determination can be achieved by using several morphological or metric traits of the skull and postcranial skeleton, which have been found to have varying degrees of accuracy. In 1969 Phenice proposed a methodology focusing on three traits located on the pubis. These traits were described as either having a female or male morphology with ambiguity being rare. Phenice's method became regularly utilized as it was considered to be reliable. In 2012, Klales and colleagues published a revision of Phenice's method, as they found that it did not capture the variation in the expression of the three traits. Klales and co-authors created a visual ordinal scale of 1-5 for each of the three traits Phenice originally identified, thus adding three extra possible forms of expression. The purpose of the present research was to test both the original and revised methodologies on the same skeletal population in order to evaluate their suitability for the assessment of sex. The Luís Lopes Anthropological collection in Lisbon was used; 117 males and 117 females were scored using both methodologies. The results showed that the original method performed better (96.5% accuracy) than the revised method (92.7%).

A geometric morphometric assessment of shape variation in adult pelvic morphology

OBJECTIVES

In humans, the pelvis is the most sexually dimorphic skeletal element and is often utilized in aging and sexing remains. The pelvis has become greatly relied upon in anthropological research (e.g., forensics, demographics, obstetrics, evolutionary history); however, pelvis morphology is highly variable, and very little is known about the nature, sources, patterning, and interpretation of this variation. This study aims to quantify pelvis shape variation, document sexual shape variation, and estimate the plasticity of morphology. This will ultimately give greater ability to interpret modern, archaeological, and evolutionary patterns to gain deeper insight into processes which shape human anatomy.

MATERIALS AND METHODS

Using a sample of 129 Medieval Danish skeletons, shape variation is documented in the greater sciatic notch (GSN), iliac crest (IC), arcuate line (AL), and sub-pubic angle (SPA) using 3D geometric morphometrics. The landmarking method applied here has the advantage of being applicable to fragmentary remains, rather than requiring whole bones. This allows it to be easily applied to archaeological samples and for the interpretation of separate bone features. Differences in shape were statistically analyzed by principle component analysis, linear discriminate analysis, and morphological disparity. Relationships between maximum femur length, body mass, and shape centroid size were also test by allometric regression.

RESULTS

Results quantify the sexual dimorphism and shape variation present in these features. The GSN shape is the most variable, while the AL is the least. Similarly, the IC is the only feature which shows almost no dimorphism in shape, and instead best reflects lifestyle/activity patterns. Evidence of dimorphism in the IC is likely a result of cultural labor patterns rather than genetic and hormonal influence. Finally, the shapes of the GSN, AL, and SPA are more related to body mass than to femur length, such that individuals with increased mass exhibit more classically "male" shapes and those with less mass have more "female" shapes.

DISCUSSION

The results have important implications for the evolution of pelvic anatomy, and sexual dimorphism, but also highlight the plasticity inherent in pelvic morphology. Analyzing pelvis features separately in a clearly defined, relatively genetically homogenous population gives insight into the determinants of bone morphology, which are not readily observable by other means. The relationship between body mass and shape suggests dimorphism in body size and composition may affect bone shape.

Influence of climatic stress on nonmetric sexually dimorphic features of the skull and pelvis

OBJECTIVES

Human sexual dimorphism is frequently assessed through skull and pelvic size and shape. Researchers suggest that climatic variation and the associated stress may be significant factors in sexual dimorphism's etiology. However, little research has specifically investigated climatic effects on nonmetric skeletal indicators of sex. To further appreciate the plasticity of human biology, a comparative study of standard skull and pelvic nonmetric sex indicators is presented.

METHODS

A Native Alaskan archeological sample (n = 104) and a component of the Terry collection (n = 99) represent populations originating from different climatic environments in recent history. These sex-balanced groups are compared through Tukey-Kramer's method and Greene's t-test to determine any variation in degree of sexual dimorphism within and between samples.

RESULTS

The results reinforce the complex and multifaceted relationship between climate and sexual dimorphism. The Terry sample demonstrated a greater degree of sexual dimorphism with statistically significant differences in robusticity of the mastoid process and nuchal crest compared with the Native Alaskans. A more "male" morphotype and reduced dimorphism are appreciated in the pelves of Native Alaskans than the Terry sample.

CONCLUSIONS

This research highlights a reduction in sexual dimorphism in populations under greater climatic stress and contributes to the production of more accurate skeletal assessments in future investigations. Discussion of confounding factors suggest more research is necessary to untangle climate and human morphology's complex relationship. This study contributes to a greater appreciation of human biological plasticity, ecogeographic variation, and the evolution of modern human diversity.

The accuracy of 3D virtual bone models of the pelvis for morphological sex estimation

It is currently unknown whether morphological sex estimation traits are accurately portrayed on virtual bone models, and this hampers the use of virtual bone models as an alternative source of contemporary skeletal reference data. This study determines whether commonly used morphological sex estimation traits can be accurately scored on virtual 3D pelvic bone elements. Twenty-seven intact cadavers from the body donation program of the Amsterdam UMC, University of Amsterdam, were CT scanned; this data was used to produce virtual bone models. Thereafter, the dry bones were obtained. Three traits by Klales (2012) and five traits from the Workshop of European Anthropologists (WEA) (1980) were scored on the virtual bone models and their dry skeletal counterparts. Intra- and inter-observer agreement and the agreement between the scores for each virtual bone model-dry bone pair were calculated using weighted Cohen’s kappa (K). For all Klales (2012) traits, intra- and inter-observer agreement was substantial to almost perfect for the virtual- and dry bones (K = 0.62–0.90). The agreement in scores in the virtual-dry bone pairs ranged from moderate to almost perfect (K = 0.58–0.82). For the WEA (1980) traits, intra-observer agreement was substantial to almost perfect (K = 0.64–0.91), but results were less unambiguous for inter-observer agreement (K = 0.24–0.88). Comparison of the scores between the virtual bone models and the dry bones yielded kappa values of 0.42–0.87. On one hand, clinical CT data is a promising source for contemporary forensic anthropological reference data, but the interchangeability of forensic anthropological methods between virtual bone models and dry skeletal elements needs to be tested further.

Oval in males and triangular in females? A quantitative evaluation of sexual dimorphism in the human obturator foramen

Among the numerous pelvic traits presenting sex differences, the obturator foramen is classically described as being oval in males and triangular in females. However, no demonstrations or detailed studies seem available in the literature. The purpose of this work was to study quantitatively this trait using Fourier analysis, because this methodological approach is particularly well adapted for discrimination between different simple shapes. Using this approach, an outline can be characterized by a series of harmonics (1 to n), each defined by two Fourier descriptors: amplitude (C(n)), describing the relative importance of the harmonic contribution to the original shape, and phase (Phi(n)), representing the orientation of the harmonic contribution. The material consisted of 104 three-dimensional CT reconstructions of adult pelves (52 males and 52 females). After size normalization, the outlines of the 104 left obturator foramens were studied. Significant differences were demonstrated with, in total, 84.6% of individuals presenting a correct inferred sex. The most discriminating descriptors were the phase of the second harmonic (C(2),) related to the oval (or elliptic) aspect and thus the elongation of the shape, and the amplitude of the third harmonic (Phi(3)), describing the triangularity of the shape. Because the trend for an outline to be more or less oval or triangular is difficult to visually assess and because there is an infinite number of transitional shapes, only a precise quantitative approach such as Fourier analysis allows for unambiguous characterization and statistical analysis.

Pubis growth study: Applicability in sexual and age diagnostic

The growth of five variables of the ischiopubic area was analyzed from bone material from birth to old age. The main purpose was to evaluate its significance and capacity for age and sex determination during and after growth. The material used consisted of 327 specimens from four documented Western European collections. Growth curves were calculated by polynomial regression for two classical variables of the ischiopubic area (pubis length and ischiopubic index) and three new variables of the pubic acetabular area (horizontal and vertical diameter of the pubic acetabular area and the pubic acetabular index). None of the curves showed lineal growth, with the exception of the ischiopubic index and the masculine vertical diameter of the pubis acetabular area. Pubis length has the most complicated growth, expressed by a five-degree polynomial. All the variables are useful for adult sex determination, except the pubic acetabular index. The ischopubic index, vertical diameter of the pubic acetabular area and the pubic acetabular index seem to be good variables for sub-adult sex determination. For age estimation the best variables, in both archaeological and forensic remains, are the absolute measurements (pubic length, vertical and horizontal diameter of the pubis). However, pubis length is the best variable for age estimation because it can be applied until 25 years of age.

Sexual dimorphism of acetabulum–pubis index in South-Indian population

Accurate sexing of skeletal remains is a vital part of any medicolegal investigation and a challenge to physical anthropologists. Hipbone is considered as the most reliable sex indicator in the human skeleton. Standards of morphological and morphometric sex differences in the skeleton may differ with the population sample involved and thus cannot be applied universally. The acetabulum-pubis index (A-P index) which is one of the reliable criteria for sex differentiation of human hipbones is derived from the measurements of acetabulum diameter and the distance between its anterior rim and symphysis pubis. Sixty-seven adult hipbones of known sex (36 males and 31 females) belonging to South-Indian population were studied to investigate sexual dimorphism of the well established A-P index. The index below 77.5 identified 81% of females and above 77.5 identified 83% males accurately.

Greater sciatic notch morphology: Sex, age, and population differences

The accuracy of a method for visually scoring sex differences in the greater sciatic notch was tested on 296 skeletons of known age and sex. The proportion of correct sex assignments is 80% when all specimens are classified, and 89% when os coxae assigned the score in which the sexes show the greatest overlap are excluded. Although many os coxae (35%) have this sexually intermediate morphology, excluding them has the advantage of substantially reducing sex biases in sexing errors. For both sexes, there is a strong relationship between age at death and sciatic notch score. People who die at a younger age tend to have wider, more feminine-appearing sciatic notches than people of greater longevity. There are also significant population differences. The 18th-19th century English sample from St. Bride's Church has a more feminine morphology than Americans of European or African ancestry. Environmental influences on skeletal development (vitamin D deficiency) appear to provide the most likely explanation for these population differences.

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.

Reliability test of the visual assessment of cranial traits for sex determination

Interobserver variation in visual evaluation was analyzed for 10 cranial traits in a homogeneous archaeological series. Two observers independently scored cranial traits commonly used for determination of sex. Though determination of sex did not differ significantly for the two observers, individual traits had different levels of interobserver reliability. In addition, indices of relative "maleness" and "femaleness" derived by the two observers differed at statistically significant levels. Because such indices are used in cross-population comparisons of relative gracility and robusticity of diverse samples, these comparisons should be interpreted with caution when more than one investigator has performed an assessment. Most of our instances of interobserver discordance derived from character traits described in subjective terms without accompanying diagrams. Clarity of definition, rather than number of character traits, was found to be critical for effective determination of sex by the visual assessment method. Use of fewer, more precisely defined character traits can improve interobserver reliability.

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.

Sex differences in the sciatic notch of great apes and modern humans

The sciatic notch has been widely used as a sexing criterion in modern humans. In order to better understand the sex differences of this feature in modern humans and great apes, four measurements of the sciatic notch were taken on samples of modern humans and great apes of known sex. Univariate (ANOVA) analysis and discriminant function analysis were performed on the extant taxa to determine: (1) the discriminating power of each variable in these samples of known group membership; and (2) which of these extant taxa shows the best discrimination between the sexes for the sciatic notch. Of the four extant taxa, the sciatic notch of Homo sapiens is the most sexually dimorphic, followed by Gorilla gorilla, and more weakly by Pongo pygmaeus, while Pan troglodytes is the least dimorphic of these taxa. Since the presence of a well defined sciatic notch is a hominid trait resulting from the dorsal extension of the posterior ilium, the close approximation of the sacrum to the acetabulum, the shortened ischium, and the accentuation of the ischial spine as part of the bipedal adaptation, it seems likely that the configuration of the sciatic notch in hominids was initially related to bipedalism, not reproduction. The development of sex differences in the sciatic notch of modern humans is more likely to have occurred after the transition to bipedality.