The Development and Use of Computational Tools in Forensic Science.

Modern computational resources make available a rich tool kit of statistical methods that can be applied to forensic questions. This tool kit is built on the foundation of statistical developments dating back to the 19th century. To fully and effectively exploit these developments, both the makers and users of software must be keenly aware of the quality, that is, the accuracy and precision, of the data being modeled or analyzed, and end users must be sufficiently familiar with the underlying theory to understand the process and results of any analysis or software they use. This is especially important for medicolegal personnel who might be called upon to testify in a court of law and be subject to cross-examination. With respect to the development of computational tools, it is increasingly important that they be made available as open-source code to avoid the pitfalls of commercial software support and the potential dependence of end users on orphaned software.

Age-at-Death Estimation for Modern Populations in Mexico and Puerto Rico through the Use of 3D Laser Scans of the Pubic Symphysis.

Reliable age-at-death estimates from the adult skeleton are of fundamental importance in forensic anthropology, because it contributes to the identity parameters used in a medicolegal death investigation. However, reliable estimates are difficult because many traditional aging methods depend on a set of population-specific criteria derived from individuals of European and African descent. The absence of information on the potential differences in the aging patterns of underrepresented, especially Latinx, populations may hinder our efforts to produce useful age-at-death estimates. In response to these concerns, this study explores the utility of currently available aging techniques and whether population-specific aging methods among Latinx groups are needed. The authors obtained data from two skeletal collections representing modern individuals of Mexican and Puerto Rican origin. They examined five newly developed computational shape-based techniques using 3D laser scans of the pubic symphysis and one traditional bone-to-phase technique. A validation test of all computational and traditional methods was implemented, and new population-specific equations using the computational algorithms were generated and tested against a subsample. Results suggest that traditional and computational aging techniques applied to the pubic symphysis perform best with individuals within 35-45 years of age. Levels of bias and inaccuracy increase as chronological age increases, with overestimation of individuals younger than 35 years and underestimation of individuals older than 45 years. New regression models provided error rates comparable to, and in some occasions outperformed, the original computational models developed on white American males, but age estimates did not significantly improve. This study shows that population-specific models do not necessarily improve age estimates in Latinx samples. Results do suggest that computational methods can ultimately outperform the Suchey-Brooks method and provide improved objectivity when estimating age at death in Latinx samples.

An enhanced computational method for age-at-death estimation based on the pubic symphysis using 3D laser scans and thin plate splines.

OBJECTIVES: The pubic symphysis is frequently used to estimate age-at-death from the adult skeleton. Assessment methods require the visual comparison of the bone morphology against age-informative characteristics that represent a series of phases. Age-at-death is then estimated from the age-range previously associated with the chosen phase. While easily executed, the "morphoscopic" process of feature-scoring and bone-to-phase-matching is known to be subjective. Studies of method and practitioner error demonstrate a need for alternative tools to quantify age-progressive change in the pubic symphysis. This article proposes a more objective, quantitative method that analyzes three-dimensional (3D) surface scans of the pubic symphysis using a thin plate spline algorithm (TPS). MATERIALS AND METHODS: This algorithm models the bending of a flat plane to approximately match the surface of the bone and minimizes the bending energy required for this transformation. Known age-at-death and bending energy were used to construct a linear model to predict age from observed bending energy. This approach is tested with scans from 44 documented white male skeletons and 12 casts. RESULTS: The results of the surface analysis show a significant association (regression p-value = 0.0002 and coefficient of determination = 0.2270) between the minimum bending energy and age-at-death, with a root mean square error of ≈19 years. DISCUSSION: This TPS method yields estimates comparable to established methods but offers a fully integrated, objective and quantitative framework of analysis and has potential for use in archaeological and forensic casework.

Influence of edentulism on human orbit and zygomatic arch shape.

Edentulism, or tooth loss, seriously alters the appearance of the lower facial skeleton. The aim of this study was to determine if complete maxillary edentulism also impacts the curvature shape of the orbits and zygomatic arches in elderly adults. The study was conducted on 80 crania comprising two cross-sectional populations of elderly African- and European-Americans (60-80 years old). Forty of the crania possessed intact dentition; the remaining 40 exhibited complete edentulism with tooth socket resorption. Three-dimensional semilandmarks representing the curvature of the orbits and zygomatic arches were collected using a hand-held digitizer. Each craniofacial region's semilandmarks were aligned into a common coordinate system via generalized Procrustes superimposition. Regional variation in shape was explored via principal component analysis, multivariate analysis of variance, discriminant function analysis, cross-validation, and vector plots. Shape differences between the edentulous and dentate groups were detected in both the orbits (P = 0.0022) and zygomatic arches (P = 0.0026). Ancestry and sex differences were also identified in both regions. Orbit data correctly classified dentate crania 65% of the time and edentulous crania 72.5% of the time. Zygomatic arch data correctly classified 75% dentate and 60% of edentulous crania. The individual curves constituting each region also exhibited shape alteration with tooth loss, with the exception of the inferior zygomatic curve. Vector plots revealed patterns of superoinferior expansion, and medial and lateral recession depending on the region examined. These results suggest a relationship exists between maxillary edentulism and changes in the surrounding craniofacial structures.

Viewpoints: diet and dietary adaptations in early hominins: the hard food perspective.

Recent biomechanical analyses examining the feeding adaptations of early hominins have yielded results consistent with the hypothesis that hard foods exerted a selection pressure that influenced the evolution of australopith morphology. However, this hypothesis appears inconsistent with recent reconstructions of early hominin diet based on dental microwear and stable isotopes. Thus, it is likely that either the diets of some australopiths included a high proportion of foods these taxa were poorly adapted to consume (i.e., foods that they would not have processed efficiently), or that aspects of what we thought we knew about the functional morphology of teeth must be wrong. Evaluation of these possibilities requires a recognition that analyses based on microwear, isotopes, finite element modeling, and enamel chips and cracks each test different types of hypotheses and allow different types of inferences. Microwear and isotopic analyses are best suited to reconstructing broad dietary patterns, but are limited in their ability to falsify specific hypotheses about morphological adaptation. Conversely, finite element analysis is a tool for evaluating the mechanical basis of form-function relationships, but says little about the frequency with which specific behaviors were performed or the particular types of food that were consumed. Enamel chip and crack analyses are means of both reconstructing diet and examining biomechanics. We suggest that current evidence is consistent with the hypothesis that certain derived australopith traits are adaptations for consuming hard foods, but that australopiths had generalized diets that could include high proportions of foods that were both compliant and tough.

Microwear, mechanics and the feeding adaptations of Australopithecus africanus.

Recent studies of dental microwear and craniofacial mechanics have yielded contradictory interpretations regarding the feeding ecology and adaptations of Australopithecus africanus. As part of this debate, the methods used in the mechanical studies have been criticized. In particular, it has been claimed that finite element analysis has been poorly applied to this research question. This paper responds to some of these mechanical criticisms, highlights limitations of dental microwear analysis, and identifies avenues of future research.

The feeding biomechanics and dietary ecology of Australopithecus africanus.

The African Plio-Pleistocene hominins known as australopiths evolved a distinctive craniofacial morphology that traditionally has been viewed as a dietary adaptation for feeding on either small, hard objects or on large volumes of food. A historically influential interpretation of this morphology hypothesizes that loads applied to the premolars during feeding had a profound influence on the evolution of australopith craniofacial form. Here, we test this hypothesis using finite element analysis in conjunction with comparative, imaging, and experimental methods. We find that the facial skeleton of the Australopithecus type species, A. africanus, is well suited to withstand premolar loads. However, we suggest that the mastication of either small objects or large volumes of food is unlikely to fully explain the evolution of facial form in this species. Rather, key aspects of australopith craniofacial morphology are more likely to be related to the ingestion and initial preparation of large, mechanically protected food objects like large nuts and seeds. These foods may have broadened the diet of these hominins, possibly by being critical resources that australopiths relied on during periods when their preferred dietary items were in short supply. Our analysis reconciles apparent discrepancies between dietary reconstructions based on biomechanics, tooth morphology, and dental microwear.

Regional shape change in adult facial bone curvature with age.

Life expectancies have increased dramatically over the last 100 years, affording greater opportunities to study the impact of age on adult craniofacial morphology. This article employs a novel application of established geometric morphometric methods to examine shape differences in adult regional facial bone curvature with age. Three-dimensional semilandmarks representing the curvature of the orbits, zygomatic arches, nasal aperture, and maxillary alveolar process were collected from a cross-sectional cranial sample of mixed sex and ancestry (male and female; African- and European-American), partitioned into three age groups (young adult = 18-39; middle-aged = 40-59 years; and elderly = 60+ years). Each facial region's semilandmarks were aligned into a common coordinate system via generalized Procrustes superimposition. Regional variation in shape was then explored via a battery of multivariate statistical techniques. Age-related shape differences were detected in the orbits, zygomatic arches, and maxillary alveolar process. Interactions between age, sex, and ancestry were also identified. Vector plots revealed patterns of superoinferior compression, lateral expansion, and posterior recession depending on the population/subpopulation, location, and age groups examined. These findings indicate that adult craniofacial curvature shape is not static throughout human life. Instead, age-related spatial modifications occur in various regions of the craniofacial skeleton. Moreover, these regional alterations vary not only through time, but across human populations and the sexes.

A Study on the Asymmetry of the Human Left and Right Pubic Symphyseal Surfaces Using High-Definition Data Capture and Computational Shape Methods.

The pubic symphysis is among the most commonly used bilateral age indicators. Because of potential differences between right and left sides, it is necessary to investigate within-individual asymmetry, which can inflate age estimation error. This study uses 3D laser scans of paired pubic symphyses for 88 documented White males. Scan data are analyzed by numerical shape algorithms, proposed as an alternative to traditional visual assessment techniques. Results are used to quantify the within-individual asymmetry, evaluating if one side produces a better age-estimate. Relationships between the asymmetry and advanced age, weight, and stature are examined. This analysis indicates that the computational, shape-based techniques are robust to asymmetry (>80% of paired differences are within 10 years and >90% are within 15 years). For notably more asymmetric cases, differences in estimates are not associated with life history factors. Based on this study, either side can be used for age-at-death estimation by the computational methods.

Testing Reliability of the Computational Age-At-Death Estimation Methods between Five Observers Using Three-Dimensional Image Data of the Pubic Symphysis.

In an effort to standardize data collection and analysis in age estimation, a series of computational methods utilizing high-dimensional image data of the age indicator have recently been proposed as an alternative to subjective visual, trait-to-phase matching techniques. To systematically quantify the reproducibility of such methods, we investigate the intrascan variability and within- and between-observer reliability in initial scan data capturing and editing using 3D laser scans of the Suchey-Brooks pubic symphysis casts and five shape-based computational methods. Our results show that (i) five observers with various training background and experience levels edited the scans consistently for all three trials and the derived shape measures and age estimates were in excellent agreement among observers, and (ii) the computational methods are robust to a measured degree of scan trimming error. This study supports the application of computational methods to 3D laser scanned images for reliable age-at-death estimation, with reduced subjectivity.

Quantification of age-related shape change of the human rib cage through geometric morphometrics.

The aim of this study is to quantify patterns of age-related shape change in the human thorax using Procrustes superimposition. Landmarks (n=106) selected from anonymized computed tomography (CT) scans of 63 adult males free of skeletal pathology were used to describe the form of the rib cage. Multivariate linear regression was used to determine a relationship between landmark location and age. Linear and quadratic models were also investigated. A permutation test employing 1 x 10(5) random trials was used to assess the model significance for both model formulations. Linear relationships between the centroid size (CS) of a landmark set and the corresponding individual's height, weight, and BMI were conducted to enable scaling of the dimensionless results from the Procrustes analysis. A significance level of alpha=0.05 was used for all tests. The average age of the study subjects was 57.0+/-17.3 years. Complete landmark sets were obtained from most of the scans (44 of 63). The quadratic relationship between the age and landmark location was found to be significant (p=0.037), thereby establishing a relationship between the age and thoracic shape change. The linear relationship was mildly significant as well (p=0.073). Significant relationships between the centroid size of the dataset and subject weight, height and BMI were determined, with the best-correlated value being weight (p=0.002, R(2)=0.22). Landmark datasets calculated using the quadratic model exhibited shape change consistent with the clinical observations (increasing kyphosis and rounding of the thoracic cage). Procrustes superimposition represents a potential improvement in the approach used to generate computational models for injury biomechanics studies. The coefficients from the quadratic model are provided and can be used to generate the complete set of model landmark data points at a given age.

Face to Face : The Perception of Automotive Designs.

Over evolutionary time, humans have developed a selective sensitivity to features in the human face that convey information on sex, age, emotions, and intentions. This ability might not only be applied to our conspecifics nowadays, but also to other living objects (i.e., animals) and even to artificial structures, such as cars. To investigate this possibility, we asked people to report the characteristics, emotions, personality traits, and attitudes they attribute to car fronts, and we used geometric morphometrics (GM) and multivariate statistical methods to determine and visualize the corresponding shape information. Automotive features and proportions are found to covary with trait perception in a manner similar to that found with human faces. Emerging analogies are discussed. This study should have implications for both our understanding of our prehistoric psyche and its interrelation with the modern world.

A Computational Framework for Age-at-Death Estimation from the Skeleton: Surface and Outline Analysis of 3D Laser Scans of the Adult Pubic Symphysis.

In forensic anthropology, age-at-death estimation typically requires the macroscopic assessment of the skeletal indicator and its association with a phase or score. High subjectivity and error are the recognized disadvantages of this approach, creating a need for alternative tools that enable the objective and mathematically robust assessment of true chronological age. We describe, here, three fully computational, quantitative shape analysis methods and a combinatory approach that make use of three-dimensional laser scans of the pubic symphysis. We report a novel age-related shape measure, focusing on the changes observed in the ventral margin curvature, and refine two former methods, whose measures capture the flatness of the symphyseal surface. We show how we can decrease age-estimation error and improve prior results by combining these outline and surface measures in two multivariate regression models. The presented models produce objective age-estimates that are comparable to current practices with root-mean-square-errors between 13.7 and 16.5 years.

A Landmark-Free Method for Three-Dimensional Shape Analysis.

BACKGROUND: The tools and techniques used in morphometrics have always aimed to transform the physical shape of an object into a concise set of numerical data for mathematical analysis. The advent of landmark-based morphometrics opened new avenues of research, but these methods are not without drawbacks. The time investment required of trained individuals to accurately landmark a data set is significant, and the reliance on readily-identifiable physical features can hamper research efforts. This is especially true of those investigating smooth or featureless surfaces. METHODS: In this paper, we present a new method to perform this transformation for data obtained from high-resolution scanning technology. This method uses surface scans, instead of landmarks, to calculate a shape difference metric analogous to Procrustes distance and perform superimposition. This is accomplished by building upon and extending the Iterative Closest Point algorithm. We also explore some new ways this data can be used; for example, we can calculate an averaged surface directly and visualize point-wise shape information over this surface. Finally, we briefly demonstrate this method on a set of primate skulls and compare the results of the new methodology with traditional geometric morphometric analysis.

Modeling masticatory muscle force in finite element analysis: sensitivity analysis using principal coordinates analysis.

Our work on a finite element model of the skull of Macaca aims to investigate the functional significance of specific features of primate skulls and to determine to which of the input variables (elastic properties, muscle forces) the model behavior is most sensitive. Estimates of muscle forces acting on the model are derived from estimates of physiological cross-sectional areas (PCSAs) of the jaw muscles scaled by relative electromyographic (EMG) amplitudes recorded in vivo. In this study, the behavior of the model was measured under different assumptions regarding the PCSAs of the jaw muscles and the latency between EMG activity in those muscles and the resulting force production. Thirty-six different loading regimes were applied to the model using four different PCSA sets and nine different PCSA scaling parameters. The four PCSA sets were derived from three different macaque species and one genus average, and the scaling parameters were either EMGs from 10, 20, 30, 40, 50 and 60 msec prior to peak bite force, or simply 100%, 50%, or 25% of peak muscle force. Principal coordinates analysis was used to compare the deformations of the model produced by the 36 loading regimes. Strain data from selected sites on the model were also compared with in vivo bone strain data. The results revealed that when varying the external muscle forces within these boundaries, the majority of the variation in model behavior is attributable to variation in the overall magnitude rather than the relative amount of muscle force generated by each muscle. Once this magnitude-related variation in model deformation was accounted for, significant variation was attributable to differences in relative muscle recruitment between working and balancing sides. Strain orientations at selected sites showed little variation across loading experiments compared with variation documented in vivo. These data suggest that in order to create an accurate and valid finite element model of the behavior of the primate skull at a particular instant during feeding, it is important to include estimates of the relative recruitment levels of the masticatory muscles. However, a lot can be learned about patterns of skull deformation, in fossil species for example, by applying external forces proportional to the estimated relative PCSAs of the jaw adductors.

Modeling Bone Surface Morphology: A Fully Quantitative Method for Age-at-Death Estimation Using the Pubic Symphysis.

The pubic symphysis is widely used in age estimation for the adult skeleton. Standard practice requires the visual comparison of surface morphology against criteria representing predefined phases and the estimation of case-specific age from an age range associated with the chosen phase. Known problems of method and observer error necessitate alternative tools to quantify age-related change in pubic morphology. This paper presents an objective, fully quantitative method for estimating age-at-death from the skeleton, which exploits a variance-based score of surface complexity computed from vertices obtained from a scanner sampling the pubic symphysis. For laser scans from 41 modern American male skeletons, this method produces results that are significantly associated with known age-at-death (RMSE = 17.15 years). Chronological age is predicted, therefore, equally well, if not, better, with this robust, objective, and fully quantitative method than with prevailing phase-aging systems. This method contributes to forensic casework by responding to medico-legal expectations for evidence standards.

Biomechanical implications of intraspecific shape variation in chimpanzee crania: moving toward an integration of geometric morphometrics and finite element analysis.

In a broad range of evolutionary studies, an understanding of intraspecific variation is needed in order to contextualize and interpret the meaning of variation between species. However, mechanical analyses of primate crania using experimental or modeling methods typically encounter logistical constraints that force them to rely on data gathered from only one or a few individuals. This results in a lack of knowledge concerning the mechanical significance of intraspecific shape variation that limits our ability to infer the significance of interspecific differences. This study uses geometric morphometric methods (GM) and finite element analysis (FEA) to examine the biomechanical implications of shape variation in chimpanzee crania, thereby providing a comparative context in which to interpret shape-related mechanical variation between hominin species. Six finite element models (FEMs) of chimpanzee crania were constructed from CT scans following shape-space Principal Component Analysis (PCA) of a matrix of 709 Procrustes coordinates (digitized onto 21 specimens) to identify the individuals at the extremes of the first three principal components. The FEMs were assigned the material properties of bone and were loaded and constrained to simulate maximal bites on the P(3) and M(2) . Resulting strains indicate that intraspecific cranial variation in morphology is associated with quantitatively high levels of variation in strain magnitudes, but qualitatively little variation in the distribution of strain concentrations. Thus, interspecific comparisons should include considerations of the spatial patterning of strains rather than focus only on their magnitudes.

The feeding biomechanics and dietary ecology of Paranthropus boisei.

The African Plio-Pleistocene hominins known as australopiths evolved derived craniodental features frequently interpreted as adaptations for feeding on either hard, or compliant/tough foods. Among australopiths, Paranthropus boisei is the most robust form, exhibiting traits traditionally hypothesized to produce high bite forces efficiently and strengthen the face against feeding stresses. However, recent mechanical analyses imply that P. boisei may not have been an efficient producer of bite force and that robust morphology in primates is not necessarily strong. Here we use an engineering method, finite element analysis, to show that the facial skeleton of P. boisei is structurally strong, exhibits a strain pattern different from that in chimpanzees (Pan troglodytes) and Australopithecus africanus, and efficiently produces high bite force. It has been suggested that P. boisei consumed a diet of compliant/tough foods like grass blades and sedge pith. However, the blunt occlusal topography of this and other species suggests that australopiths are adapted to consume hard foods, perhaps including grass and sedge seeds. A consideration of evolutionary trends in morphology relating to feeding mechanics suggests that food processing behaviors in gracile australopiths evidently were disrupted by environmental change, perhaps contributing to the eventual evolution of Homo and Paranthropus.

Population affinities of 19th Century Cuban crania: implications for identification criteria in South Florida Cuban Americans.

Identification criteria, specifically discriminant function formulae derived from traditional craniometrics, currently used in South Florida for Cuban Americans and other "Hispanic" groups, are unsuitable to provide adequate biological profiles due to complex biological histories as well as widely diverse geographic origins. Florida's total population is approximately 16 million (15,982,378) individuals. Of the total population 2.682,715, or 16.8%, are self-identified as "Hispanic". South Florida (herein defined as Miami-Dade, Broward and Collier Counties) is home to 60% of the total Hispanic population of Florida with 1,291,737 (48.15%) residing in Miami-Dade County. The Hispanic population of Miami-Dade County makes up 57.0% of the total population of 2,253,362. Each recognized sub-group of Hispanics (Mexican, Puerto Rican, and Cuban) includes its own geographic point-of-origin and population history. Cuban-Americans (arriving in the late 1950's and early 1960's) make up the largest sub-population of Florida's Hispanics in any county and in Miami-Dade number 650,601 or 51% of the total Latin population. Additionally, as in other agricultural states, Florida has a very large population of undocumented workers who primarily arrive from Texas and points south of the Straits of Florida. Thus the application of the available traditional craniometric and non-metric methods are not appropriate for South Florida's Latin population. To begin to address this issue in relation to South Florida's Cuban population, we present an analysis of cranio-facial shape variation in a 19th Century Cuban sample, 17th Century Spanish sample, a Precontact Cuban sample, and Terry Blacks using geometric morphometric methods. Significant biological shape differences and patterns of variation are observed among the groups. These results provide us with a context in which to begin to understand the biological variation of Cuban Americans, which will enable the development of identification criteria specific for this U.S. hybrid Hispanic community.

Anthropology takes control of morphometrics.

There has been a startling change over the last decade in the intellectual context of morphometrics. In the 1990's, this field, which has not altered its focus upon the quantitative analysis of biomedical shape variation and shape change, was principally centered around concerns of medical image analysis; but now it is driven mainly by the demands of researchers in human variability, physical anthropology, primatology, and paleoanthropology instead. This essay celebrates that change and tries to account for it by reference to cognitive and intellectual aspects of the new home.