Quantification of Maxillary Dental Arcade Curvature and the Estimation of Biological Ancestry in Forensic Anthropology

Previous studies suggest that palate shape is a useful indicator of biological ancestry in human remains. This study evaluates interobserver error in ancestry estimation using palate shape and explores palate shape variation in Gullah (descendants of West Africans) and Seminole (Indigenous American) population samples using geometric morphometric analysis. Ten participants were asked to ascribe biological ancestry and shape to 28 dental casts based on a classification scheme employed in previous studies. The mean correct classification was 42.0%, indicating that the likelihood of assigning the correct ancestry is very poor and not significantly different from random assignment (p = 0.12). The accuracy analysis based on categorical classification of the casts was complemented by geometric morphometric analysis of nine 3D landmarks reflecting palate shape of 158 casts. Principal component analysis results show no difference between populations regarding palate shape, and cross‐validated discriminant function analysis correctly classified only 62.0% of the specimens. Combined, these results show that previous methods to estimate ancestry are inaccurate and that this inaccuracy is probably due to a lack of palate shape differences between groups, rather than limitation of the analytical method per se. Therefore, we recommend caution should be used when choosing to apply the analysis of palate shape in forensically relevant contexts.     

Demographic change and forensic identification: problems in metric identification of Hispanic skeletons

The United States (U.S.) population structure is currently in a state of flux with one of the most profound changes being the increasing number of people referred to as Hispanic. In the U.S., much of the identification criteria for a biological profile are based on American Black and White individuals from anatomical collections. Using metric data from the Forensic Anthropology Data Bank (FDB), this paper will attempt to explore several issues that forensic anthropologists face when confronted with Hispanic remains. These will involve estimation of sex, height, and ancestry, the initial components of a biological profile. Discriminant function analyses indicate that American White criteria provide poor estimations of sex when applied to Hispanics and that ancestry estimation of Hispanic crania is difficult. Additionally, a new linear regression equation is presented that estimates stature for Hispanic individuals, although population specific criteria are still needed for Hispanic individuals from diverse geographical origins.     

Forensic Applicability of Femur Subtrochanteric Shape to Ancestry Assessment in Thai and White American Males

Ancestry assessment from the postcranial skeleton presents a significant challenge to forensic anthropologists. However, metric dimensions of the femur subtrochanteric region are believed to distinguish between individuals of Asian and non‐Asian descent. This study tests the discriminatory power of subtrochanteric shape using modern samples of 128 Thai and 77 White American males. Results indicate that the samples' platymeric index distributions are significantly different (p ≤ 0.001), with the Thai platymeric index range generally lower and the White American range generally higher. While the application of ancestry assessment methods developed from Native American subtrochanteric data results in low correct classification rates for the Thai sample (50.8–57.8%), adapting these methods to the current samples leads to better classification. The Thai data may be more useful in forensic analysis than previously published subtrochanteric data derived from Native American samples. Adapting methods to include appropriate geographic and contemporaneous populations increases the accuracy of femur subtrochanteric ancestry methods.     

Ancestral Variation in Orbital Rim Shape: A Three‐Dimensional Pilot Study

Traditional nonmetric methods of ancestry assessment posit orbital rim shape varies among ancestral groups. This pilot study uses morphometric analysis of 3D orbital variation to test discrimination among individuals of primarily European, African, and Asian ancestry. Although the size and nature of the sample analyzed limit inferences for other samples, principal components analysis suggests ancestry has a significant effect on rim shape (p = 2.93e‐04). European orbits display more marked folding of the orbit in the sagittal plane than either African or Asian orbits, while the lateral margin of African orbits lies further posterior relative to the medial margin when compared to Asian orbits. The findings suggest curviplanar relationships are the most ancestrally informative aspect of orbital rim shape; these relationships may be distorted by perspective based on orientation of the skull relative to the viewer in traditional nonmetric analyses. Additional studies on geometric morphometric approaches to ancestry assessment are therefore warranted.     

Identifying Southwest Hispanics using nonmetric traits and the cultural profile

Due to the increasing number of Southwest Hispanics in the United States, as well as the overwhelming number of foreign nationals that die every year trying to enter the United States along the southern United States border with Mexico, new methods for classifying individuals have been established at the Pima County Office of the Medical Examiner in Tucson, Arizona (PCOME). For each of the past 5 years, the PCOME has investigated a record number of deaths associated with these border crossings. The overwhelming majority of the identified decedents are Mexican Nationals. However, approximately 25% of these undocumented border crossers have yet to be identified, making it clear that improved methods for human identification are greatly needed. The first goal of this paper is to delineate the suite of skeletal nonmetric traits utilized in assessing Southwest Hispanic ancestry at the PCOME. This suite of nonmetric traits has proven to be an effective component in establishing the "biological profile" of unknown individuals in these cases. The second goal of this paper is to introduce methods used at the PCOME to establish the "cultural profile" of individuals in these cases. The "cultural profile" is a set of identification criteria that include: the geographic context of recovery, personal effects, dental health, and cultural accoutrements. Establishing the "cultural profile" in these cases is essential in identifying individuals as foreign nationals who have died trying to cross the border.     

Ancestry Estimation in Forensic Anthropology: Geometric Morphometric versus Standard and Nonstandard Interlandmark Distances

Standard cranial measurements are commonly used for ancestry estimation; however, 3D digitizers have made cranial landmark data collection and geometric morphometric (GM) analyses more popular within forensic anthropology. Yet there has been little focus on which data type works best. The goal of the present research is to test the discrimination ability of standard and nonstandard craniometric measurements and data derived from GM analysis. A total of 31 cranial landmarks were used to generate 465 interlandmark distances, including a subset of 20 commonly used measurements, and to generate principal component scores from procrustes coordinates. All were subjected to discriminant function analysis to ascertain which type of data performed best for ancestry estimation of American Black and White and Hispanic males and females. The nonstandard interlandmark distances generated the highest classification rates for females (90.5%) and males (88.2%). Using nonstandard interlandmark distances over more commonly used measurements leads to better ancestry estimates for our current population structure.     

The uniqueness of the human anterior dentition: a geometric morphometric analysis

The analysis of bitemarks has a significant bearing on forensic odontology and has attracted an increasingly sophisticated array of techniques in its evaluation. Two postulates underlie all bitemark analyses: firstly, that the characteristics of the anterior teeth involved in the bite are unique, and secondly, that this uniqueness is accurately recorded in the material bitten. Here, we investigate the question of the uniqueness of the anterior dentition. To do this, we use geometric morphometric techniques based on landmark and semilandmark data. The incisor and canine occlusal surfaces of 50 randomly selected orthodontic casts of young individuals (17-20 years) of both sexes form the material for this study. We analyzed the sizes of these teeth by means of landmark and semilandmark analysis to calculate Procrustes distances between tooth outlines. In order to analyze shape variation among individuals, we carried out principal components analyses on the partial warp scores. These are derived from Partial Procrustes coordinates aligned by means of thin-plate spline decomposition based on the bending energy matrix. The results indicate that there is no sexual dimorphism in the shape of the upper or lower arches. Plots of centroid size and first relative warps show less superposition among individuals than in shape analysis. This means that, when the size and shape are considered together, the difference between arches increases. Procrustes superimposition between the two individuals located most closely (0.0444) and the two most separated (0.1567) along the first axis of relative warp analyses show that individuals are not only differentiated by the relative position of their teeth but also by their arch shape. In conclusion, it appears that the incisal surfaces of the anterior dentition are in fact unique.     

An Exploration of Sample Representativeness in Anthropometric Facial Comparison*

Abstract: Faces are assumed to be unique, but their use in court has remained problematic as no method of comparison with known error rates has been accepted by the scientific community. Rather than relying on the assumed uniqueness of facial features, previous research has been directed at estimations of face shape frequency. Here, the influence of age, sex, and ancestry on variation was investigated. Statistical shape analysis was used to examine the necessity for sub‐divisions in forensic comparisons, using a large sample of facial images on which 30 anthropometric landmark points had been placed in 3D. Results showed a clear pattern of separation of the sexes in all age groups, and in different age groups in men. It was concluded that sub‐division of databases by sex will be necessary in forensic comparisons. Sub‐division by age may be necessary in men (although not necessarily in women), and may be necessary by ancestry.     

Microscopical discrimination of human head hairs sharing a mitochondrial haplogroup

In forensic analyses, determining the level of consensus among examiners for hair comparison conclusions and ancestry identifications is important for assessing the scientific validity of microscopical hair examinations. Here, we present data from an interlaboratory study on the accuracy of microscopical hair comparisons among a subset of experienced hair examiners currently analyzing hair in forensic laboratories across the United States. We examined how well microscopical analysis of hair can reliably be used to differentiate hair samples, many of which were macroscopically similar. Using cut hair samples, many sharing similar macroscopic and microscopic features, collected from individuals who share the same mitochondrial haplogroup as an indication of genetic relatedness, we tested multiple aspects that could impact hair comparisons. This research tested the extent to which morphological features related to ancestry and hair length influence conclusions. Microscopical hair examinations yielded accurate assessments of inclusion/exclusion relative to the reference samples among 85% of the pairwise comparisons. We found shorter hairs had reduced levels of accuracy and hairs from populations examiners were not familiar with may have impacted their ability to resolve features. The reliability of ancestry determinations is not yet clear, but we found indications that the existing categories are only somewhat related to current ethnic and genetic variation. Our results provide support for the continued utility of microscopical comparison of hairs within forensic laboratories and to advocate for a combined analytical approach using both microscopical analysis and mtDNA data on all forensic analyses of hair.     

Racial variation in the proximal and distal femur: heritability and forensic utility.

The femur has been studied successfully by physical anthropologists for many years. Such traits as femoral head diameter and bicondylar width have been examined extensively and are of great value to forensic anthropologists and other skeletal biologists in sex identification. A number of studies over the past decade by the author and his former students have shown marked racial differences in the shape of the proximal femur and in at least one trait of the distal femur--intercondylar notch height. Anterior-posterior (AP) diameter of the proximal femur is much greater among Whites and Blacks than among East Asians and American Indians. Blacks have slightly greater intercondylar notch height than Whites. Other features, such as torsion, also differ between the major geographic racial populations. Current analysis suggests that the East Polynesians fall close to the American Indians and East Asians in the degree of flatness of the proximal femur. One study has tracked the degree of change in flatness during individual development, and finds little change within major populations from the youngest to the oldest individuals. Temporal changes within populations are likewise minimal. Two studies have examined sex differences within populations, which are also found to be very slight. Racial differences, on the other hand, are quite significant, and individuals of admixed ancestry fall intermediate between the two parental populations. Such suggestions of high heritability in the shape of the proximal and distal femur make these traits very useful in assessing ancestry in forensic contexts.     

Variability of the Entire Mitochondrial DNA Control Region in a Human Isolate from the Pas Valley (Northern Spain)

Abstract: In this study, we analyzed the entire mtDNA control region in 61 unrelated individuals from the Pas Valley (Cantabria), a human isolate from northern Spain, to evaluate the suitability of this analysis to increase the power of discrimination of this locus for forensic purposes in human isolates. Low values obtained for the diversity parameters confirmed the relative isolation of this human group. The main findings of this study indicated that even the analysis of the entire mtDNA control region may have important limitations for use in forensic casework when dealing with human isolates: none of the 44 individuals who exhibited identical HVI‐HVII haplotypes could be further differentiated by analysis of segment HVIII. Nevertheless, analysis of the entire mtDNA control region proved to be useful to determine the ancestry of the samples examined, by contributing to the confirmation, and, on occasion, even to the refinement of the haplogroup assignment.     

Language use in ancestry research and estimation

Recent discussions have revolved around the concept of ancestry and ancestry estimation; however, the associated terminology and its theoretical underpinnings have not been similarly examined. This research evaluates the concepts (e.g., race, ancestry, ethnicity) currently in use, examines if they are consistent with the groups employed to illustrate them (e.g., Black, European, Hispanic), and looks for patterns in language usage. Articles in the Anthropology, Odontology, and General sections of the Journal of Forensic Sciences between 2009 and 2019 were evaluated for ancestry‐related language use. For each article, the concepts, examples, and bibliographic information were recorded, and the relationship between concept and example was examined. These data were cross‐tabulated to evaluate relationships between the variables. Cramer's V was used to assess the strength of association of these relationships. In this sample, ancestry predominates, especially recently The concept used is significantly associated with all variables except publication date and authors’ institution(s). Despite the prevalence of the ancestry concept, racially based terms for individual groups were common. The use of ancestry, over race, in forensic contexts has been suggested to be a primarily linguistic change; these results may support that assertion. Inconsistent language usage leads to a lack of clarity in meaning among researchers and misinterpretation of the data. It is critical to recognize that inconsistencies exist, but also to understand why they exist. These results underscore the long overdue need for the inclusion of diverse perspectives in forensic anthropology, especially in the current conversations surrounding ancestry and ancestry estimation.     

Outline Shape Analysis on the Trochlear Constriction and Olecranon Fossa of the Humerus: Insights for Sex Estimation and a New Computational Tool,

Sex estimation through visual analysis of the distal humerus can contribute to establishing the biological profile of an unidentified skeletal individual. Using statistical shape modeling, the trochlear constriction open curves and olecranon fossa closed outlines of 151 humeri were digitized and analyzed. The shape configurations exhibited strikingly different degrees of sexual dimorphism when evaluated using linear discriminant analysis with leave‐one‐out cross‐validation. The trochlear constriction performed poorly, correctly classifying 63.6% of the individuals. However, the olecranon fossa showed high sexual dimorphism, presenting a 94.0% accuracy. A simpler model using only two principal components was also generated. While the accuracy is slightly inferior (88.1%), it has the advantage of being constrained to bidimensional components that were translated into morphoscopic variables within a simulator interface. This allowed us to implement the method through a web application that does not require users to be trained in landmark digitization or have knowledge of geometric morphometrics.     

Morphoscopic Trait Expression in “Hispanic” Populations

This study evaluates population variation of eight cranial morphoscopic traits using samples of known southwest Hispanics (n = 72), Guatemalans (n = 106), American Blacks (n = 146), and American Whites (n = 218). We applied the support vector machine (SVM) method to build a prediction model based on a subsample (20%) of the data; the remainder of the data was used as a test sample. The SVM approach effectively differentiated between the four groups with correct classification rates between 72% (Guatemalan group) and 94% (American Black group). However, when the Guatemalan and southwest Hispanic samples were pooled, the same model correctly classified all groups with a higher degree of accuracy (American Black = 96%; American White = 77%; and the pooled Hispanic sample = 91%). This study also identified significant differences between the two Hispanic groups in six of the eight traits using univariate statistical tests. These results speak to the unique population histories of these samples and the current use of the term “Hispanic” within forensic anthropology. Finally, we argue that the SVM can be used as a classification model for ancestry estimation in a forensic context and as a diagnostic tool may broaden the application of morphoscopic trait data for the assessment of ancestry.     

Accuracy of Dental Age in Nonadults: A Comparison of Two Methods for Age Estimation Using Radiographs of Developing Teeth

This research tests the accuracy of two methods for age estimation, Cameriere's European formula and AlQahtani's London Atlas, on a multi‐population American sample. Digitized radiographs of 360 European American, Hispanic, and American Indian children aged 6–17 years were analyzed. The accuracy of these methods was assessed using the mean and absolute mean difference of the residuals. Results indicate that Cameriere's European formula underestimated age for both sexes, with a mean difference of ?1.19 years for girls and ?1.32 years for boys, prompting the first author to create an American‐specific formula. The London Atlas underestimated age with a mean difference of ?0.18 years for girls and ?0.16 years for boys. Sex and ancestry had no significant affect on accuracy. The results indicate that both methods can be used for age estimation in an American population.     

Morphometric Analysis of the Neurocranium in an Adult South African Cadaveric Sample,

Craniometric studies of South Africans yield high accuracies of sex and ancestry classification, but most assess only inter‐group variation of Black and White individuals, excluding the highly heterogeneous Colored group, which constitute a significant proportion of the population. This study applied a geometric morphometric approach to the neurocrania of 774 Black, Colored, and White individuals to assess sex and ancestry estimation accuracy based on the detected morphological variation. Accuracies of 70% and 83% were achieved for sex and ancestry, respectively, with ancestry‐related variation contributing the largest proportion of overall observed variation. Even when comparing the closely related Black and Colored groups, relatively high accuracies were obtained. It is thus recommended that a similar approach be used to develop a contemporary three‐dimensional database, which can be used to objectively, reliably, and accurately classify unknown remains in the South African forensic context.     

A Radiographic Study on the Utility of Cranial Vault Outlines for Positive Identifications

A standard method for positive identification is the use of antemortem and postmortem radiographic comparisons. The purpose of this research is to test the visual accuracy of antemortem and postmortem radiographic comparisons of cranial vault outlines and to evaluate their uniqueness using geometric morphometric methods. A sample of 106 individuals with varying levels of education and forensic case experience participated in a visual accuracy test. Of the 106 individuals, only 42% correctly assigned all of the radiographs, with accuracy rates ranging from 70 to 93% for each radiographic comparison. Vault shape was further examined using elliptic Fourier analysis, and paired t‐tests were computed on the first 10 principal components accounting for 100% of the variance, which found no significant differences. The visual accuracy test and elliptic Fourier analysis shows that vault outlines may not be unique enough for positive identifications when used as a sole indicator.     

Discrete Traits of the Sternum and Ribs: A Useful Contribution to Identification in Forensic Anthropology and Medicine

During forensic anthropological investigation, biological profile is determined by age, sex, ancestry, and stature. However, several individuals may share the same profile. Observation of discrete traits can yield useful information and contribute to identification. This research establishes the frequency of discrete traits of the sternum and ribs in a modern population in southern France, using 500 computer tomography (CT) scans of individuals aged 15–60 years. Only discrete traits with a frequency lower than 10% according to the literature were considered, a total of eight traits. All scans examined were three‐dimensional (3D) volume renderings from DICOM images. In our population, the frequency of all the discrete traits was lower than 5%. None were associated with sex or age, with the exception of a single trait, the end of the xiphoid process. Our findings can usefully be applied for identification purposes in forensic anthropology and medicine.