Stephen D. Ousley

New perspectives in forensic anthropology.

A critical review of the conceptual and practical evolution of forensic anthropology during the last two decades serves to identify two key external factors and four tightly inter-related internal methodological advances that have significantly affected the discipline. These key developments have not only altered the current practice of forensic anthropology, but also its goals, objectives, scope, and definition. The development of DNA analysis techniques served to undermine the classic role of forensic anthropology as a field almost exclusively focused on victim identification. The introduction of the Daubert criteria in the courtroom presentation of scientific testimony accompanied the development of new human comparative samples and tools for data analysis and sharing, resulting in a vastly enhanced role for quantitative methods in human skeletal analysis. Additionally, new questions asked of forensic anthropologists, beyond identity, required sound scientific bases and expanded the scope of the field. This environment favored the incipient development of the interrelated fields of forensic taphonomy, forensic archaeology, and forensic trauma analysis, fields concerned with the reconstruction of events surrounding death. Far from representing the mere addition of new methodological techniques, these disciplines (especially, forensic taphonomy) provide forensic anthropology with a new conceptual framework, which is broader, deeper, and more solidly entrenched in the natural sciences. It is argued that this new framework represents a true paradigm shift, as it modifies not only the way in which classic forensic anthropological questions are answered, but also the goals and tasks of forensic anthropologists, and their perception of what can be considered a legitimate question or problem to be answered within the field.

Understanding race and human variation: why forensic anthropologists are good at identifying race.

American forensicanthropologists uncritically accepted the biological race concept from classic physical anthropology and applied it to methods of human identification. Why and how the biological race concept might work in forensic anthropology was contemplated by Sauer (Soc Sci Med 34 1992 107-111), who hypothesized that American forensic anthropologists are good at what they do because of a concordance between social race and skeletal morphology in American whites and blacks. However, Sauer also stressed that this concordance did not validate the classic biological race concept of physical anthropology that there are a relatively small number of discrete types of human beings. Results from Howells (Papers of the Peabody Museum of Archaeology and Ethnology 67 1973 1-259; Papers of the Peabody Museum of Archaeology and Ethnology 79 1989 1-189; Papers of the Peabody Museum of Archaeology and Ethnology 82 1995 1-108) and others using craniometric and molecular data show strong geographic patterning of human variation despite overlap in their distributions. However, Williams et al. (Curr Anthropol 46 2005 340-346) concluded that skeletal morphology cannot be used to accurately classify individuals. Williams et al. cited additional support from Lewontin (Evol Biol 6 1972 381-398), who analyzed classic genetic markers. In this study, multivariate analyses of craniometric data support Sauers hypothesis that there are morphological differences between American whites and blacks. We also confirm significant geographic patterning in human variation but also find differences among groups within continents. As a result, if biological races are defined by uniqueness, then there are a very large number of biological races that can be defined, contradicting the classic biological race concept of physical anthropology. Further, our results show that humans can be accurately classified into geographic origin using craniometrics even though there is overlap among groups.

Multivariate Quantitative Genetics of Anthropometric Traits from the Boas Data

Abstract The use of multivariate quantitative trait information to address questions of population relationships and evolutionary issues has a longstanding history in human anthropometry. Previous analyses have usually rested on a number of explicit or implicit assumptions that allow phenotypic information to be used as a proxy for quantitative genetic information. One (usually implicit) assumption is that the additive genetic variance-covariance matrix (G) among traits is proportional to the phenotypic variance-covariance matrix (P). In this study we discuss the implications of this assumption, demonstrating that if it is true that G = h 2 P, where h 2 is some constant of proportionality, then (1) the biological (phenotypic) Mahalanobis distance will be proportional to genetic distance, (2) phenotypic and genetic allometry coefficients will be equal, and (3) evolutionary models will become simplified. We then use a multivariate quantitative genetic analysis of 12 anthropometric traits in 5 tribes to demonstrate that G = h 2 P for at least a portion of the Boas data.

A revised method of sexing the human innominate using Phenice's nonmetric traits and statistical methods†

The traits of the pubis described by Phenice (Am J Phys Anthropol 30 (1969) 297-302) have been used extensively by physical anthropologist for sex estimation. This study investigates all three of Phenices characteristics in an approach similar to Walkers (Am J Phys Anthropol 136 (2008) 39-50) study using observations from the cranium and mandible. The ventral arc, the subpubic contour, and the medial aspect of the ischio-pubic ramus were scored on a five-point ordinal scale from a sample of 310 adult, left innominates of known ancestry and sex from the Hamann-Todd Human Osteological Collection and the W.M. Bass Donated Skeletal Collection. Four observers with varying levels of experience blindly scored each trait using new descriptions and illustrations adapted from those originally created by Phenice. The scores were then analyzed with ordinal logistic regression. Using all three traits for sex classification, the mean correct classification rate was 94.5% cross-validated for experienced observers. Intra- and interobserver error in trait scoring was low for all three traits and agreement levels ranged from moderate to substantial. Tests of the method on an independent validation sample provided a classification accuracy of 86.2%. This revision of the Phenice (Am J Phys Anthropol 30 (1969) 297-302) technique is a reliable and valid method of sex estimation from the human innominate that meets the Daubert criteria for court admissibility.

Statistical Classification Methods for Estimating Ancestry Using Morphoscopic Traits

Ancestry assessments using cranial morphoscopic traits currently rely on subjective trait lists and observer experience rather than empirical support. The trait list approach, which is untested, unverified, and in many respects unrefined, is relied upon because of tradition and subjective experience. Our objective was to examine the utility of frequently cited morphoscopic traits and to explore eleven appropriate and novel methods for classifying an unknown cranium into one of several reference groups. Based on these results, artificial neural networks (aNNs), OSSA, support vector machines, and random forest models showed mean classification accuracies of at least 85%. The aNNs had the highest overall classification rate (87.8%), and random forests show the smallest difference between the highest (90.4%) and lowest (76.5%) classification accuracies. The results of this research demonstrate that morphoscopic traits can be successfully used to assess ancestry without relying only on the experience of the observer.

Using multivariate adaptive regression splines to estimate subadult age from diaphyseal dimensions

Subadult age estimation is considered the most accurate parameter estimated in a subadult biological profile, even though the methods are deficient and the samples from which they are based are inappropriate. The current study addresses the problems that plague subadult age estimation and creates age estimation models from diaphyseal dimensions of modern children. The sample included 1,310 males and females between the ages of birth and 12 years. Eighteen diaphyseal length and breadth measurements were obtained from Lodox Statscan radiographic images generated at two institutions in Cape Town, South Africa, between 2007 and 2012. Univariate and multivariate age estimation models were created using multivariate adaptive regression splines. k-fold cross-validated 95% prediction intervals (PIs) were created for each model, and the precision of each model was assessed. The diaphyseal length models generated the narrowest PIs (2 months to 6 years) for all univariate models. The majority of multivariate models had PIs that ranged from 3 months to 5 and 6 years. Mean bias approximated 0 for each model, but most models lost precision after 10 years of age. Univariate diaphyseal length models are recommended for younger children, whereas multivariate models are recommended for older children where the inclusion of more variables minimized the size of the PIs. If diaphyseal lengths are not available, multivariate breadth models are recommended. The present study provides applicable age estimation formulae and explores the advantages and disadvantages of different subadult age estimation models using diaphyseal dimensions. Am J Phys Anthropol 154:376-386, 2014.

Analysis of Six Vietnamese Trophy Skulls

This report presents morphologic, metric, and contextual information on six documented trophy skull specimens confiscated from U.S. servicemen during the Vietnam War. Additional information on the history and occurrence of trophy skull collecting is provided. This sample, consisting mostly of young Vietnamese males, exhibits graffiti, painting, and other evidence of postmortem decorative modification. Identification of trophy skulls is important to medicolegal and anthropological researchers in distinguishing trophy remains from archaeological and forensic specimens.

Test of the relationship between sutural ossicles and cultural cranial deformation: Results from Hawikuh, New Mexico

A number of researchers have hypothesized that the biomechanical forces associated with cultural cranial deformation can influence the formation of sutural ossicles. However, it is still difficult to make definitive conclusions about this relationship because the effects appear to be quite weak, and contradictory results have been obtained when specific sutures and deformation types are compared across studies. This research retests the hypothesis using a single archeological sample of lamdoidally deformed, occipitally deformed, and undeformed crania from Hawikuh, New Mexico (AD 1300-1680). Our results show no significant difference in either the prevalence or number of ossicles between deformed and undeformed crania, suggesting that the abnormal strains generated by cranial shape modification during infancy are not a factor in ossicle development for this population. One significant relationship was detected at the right lambdoid suture in crania with asymmetrical occipital deformation. Crania that were more deformed on the left side showed greater numbers of ossicles on the right side, but the effect was small. Furthermore, the relationship may well reflect a sampling error, due to the small number of crania with greater left side deformation and scorable right side lambdoid ossicles (n = 11). Although it is possible that forms of cranial deformation other than the posterior tabular types examined here may affect ossicle expression, our review of the literature suggests that the relationship in humans is complex and incompletely understood at this time.

Subadult sex estimation from diaphyseal dimensions: STULL et al.

OBJECTIVES Many studies on subadult sex estimation focus on elements that express sexually dimorphic features in adults. In contrast, diaphyseal dimensions have been shown to display sex-specific differences prior to adolescence. The current study evaluates the use of diaphyseal dimensions in subadult sex estimation. MATERIALS AND METHODS Eighteen postcranial measurements from six long bones were collected on Lodox Statscan radiographic images of 1,310 modern South African children between birth and 12 years of age. Linear (LDA) and flexible discriminant analysis (FDA) and logistic regression were employed with single and multiple variable models with age both included and excluded from the model. Bootstrapped cross-validation was employed because some of the multiple variable subsets had small sample sizes. Each of the bootstrapped accuracies has an associated 95% confidence interval demonstrating the ranges in classification. RESULTS Classification methods utilizing multiple variables achieved the highest bootstrapped classification accuracies (70% to 93%). The inclusion of age in the models did not consistently increase or decrease the classification accuracies. Proximal and distal breadth measurements were consistently recognized as important measurements in model creation. FDA yielded the highest overall accuracies, but the logistic regression presented with overall smaller bootstrapped 95% confidence intervals. DISCUSSION Quantifiable sex differences were discovered in the appendicular skeleton of children between birth and 12 years of age. The high classification accuracies were likely due to using numerous predictor variables from multiple skeletal elements, which were optimized for classification using FDA. To facilitate application, a graphical user interface, KidStats, was developed.

Craniometric Variation in the Aleutians: Integrating Morphological, Molecular, Spatial, and Temporal Data

Abstract Several hypotheses have been put forward about the origins and evolution of the inhabitants of the Aleutian Islands. Both Hrdlička [The Aleutian and Commander Islands and Their Inhabitants (Philadelphia: Wistar Institute of Anatomy and Biology, 1945)] and Laughlin [“The Alaska gateway viewed from the Aleutian Islands,” in Papers on the Physical Anthropology of the American Indian, W. S. Laughlin, ed. (New York: Viking Fund, 1951), 98–126] analyzed cranial morphology and came to somewhat different conclusions using a typological approach and limited analytical methods. Subsequent investigations using morphological data have not significantly improved our understanding of Aleut prehistory. More recently, radiocarbon dating and mitochondrial DNA analyses have shed light on Aleut genetic variation and changes over time, but better morphological methods using multivariate statistical analysis have not yet been used. We analyzed craniometric data using multivariate procedures and found that Aleuts demonstrate significant changes in cranial morphology over time, and these changes correspond to Hrdličkas observations but may not necessarily reflect in-migration. The morphological changes were concentrated in the very aspects of morphology that are easily observable and that Hrdlička most often measured, namely, cranial length, breadth, and height, but they were obscured when craniometric variation as a whole was analyzed. Also, we found that the morphological changes over time were not related to the changes in haplogroup frequencies over time, suggesting that migration into the Aleutians did not play a significant role in producing the morphological changes. However, craniometric variability apparently increases over time, suggesting in-migration, localized selection, and/or greater environmental heterogeneity. Our results contradict Laughlins observations but may be more in line with his hypothesis of in situ evolutionary changes absent gene flow. In addition to selection, gene flow, and gene drift, however, sociocultural changes must also be considered as a factor in why morphology changed over time.