Marin A. Pilloud

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.

Brief communication: the use of alternative dental measurements on deciduous teeth.

The present study investigates the utility of cervical measurements in deciduous teeth and how they correlate with traditional measurements of the crown. First, this study establishes definitions by which these measurements could reliably be taken. Next, deciduous cervical and traditional crown diameters were taken on three distinct skeletal samples: a Neolithic assemblage from Central Anatolia (Çatalhöyük, n = 85), a precontact sample from Northern California (CA-ALA-329, n = 34), and a group of intrusive burials interred at Çatalhöyük that date between AD 60 and 1650 (n = 38). Across the dentition there are positive correlations between crown and cervical measurements, which tend to be higher in anterior teeth than in posterior teeth. Both measurements show low correlations with age; however, cervical measurements show fewer negative correlations with age. An intraobserver error study found low levels of error for both types of measurements. On a subset of the Çatalhöyük sample (n = 9), a principal components and biological distance analysis were conducted comparing the two types of measurements. Also, all three samples were subject to a canonical discriminant function analysis and the results from cervical and crown measurements were compared. All analyses produced slightly different results for each type of data suggesting that crown and cervical measurements capture different aspects of tooth shape. While cervical and crown measurements provide different statistical results, cervical measurements can provide information relevant to anthropological studies and may allow for larger datasets to be used by allowing the inclusion of teeth with modified crowns.

A brief history of biological distance analysis

Abstract Biological distance, or biodistance, analysis employs data derived from skeletal remains to reflect population relatedness (similarity/dissimilarity) through the application of multivariate statistical methods. The approaches used in biodistance studies have changed markedly over recent centuries, exploring phenotypic expressions assumed to be informative. Biodistance analysis began as the study of anomalous variants in the human skull, but the field has transformed over the centuries now seeking to incorporate skeletal morphology in the interpretation of genetic affinity, providing insight into the genetics governing trait expression, and providing understanding into the role of developmental biology on the expression of morphological variants. As methodological approaches improve, so too has the application of these analyses. We present here a brief historical overview of biodistance analysis research, focusing on meta-themes in the field, shifts in thinking among researchers in biological anthropology, and several of the outside influences that impact biodistance analysis.

Environmental selection during the last ice age on the mother-to-infant transmission of vitamin D and fatty acids through breast milk

Significance The frequency of the human-specific EDAR V370A isoform is highly elevated in North and East Asian populations. The gene is known to have several pleiotropic effects, among which are sweat gland density and ductal branching in the mammary gland. The former has led some geneticists to argue that the near-fixation of this allele was caused by selection for modulation of thermoregulatory sweating. We provide an alternative hypothesis, that selection instead acted on the allele’s effect of increasing ductal branching in the mammary gland, thereby amplifying the transfer of critical nutrients to infants via mother’s milk. This is likely to have occurred during the Last Glacial Maximum when a human population was genetically isolated in the high-latitude environment of the Beringia. Because of the ubiquitous adaptability of our material culture, some human populations have occupied extreme environments that intensified selection on existing genomic variation. By 32,000 years ago, people were living in Arctic Beringia, and during the Last Glacial Maximum (LGM; 28,000–18,000 y ago), they likely persisted in the Beringian refugium. Such high latitudes provide only very low levels of UV radiation, and can thereby lead to dangerously low levels of biosynthesized vitamin D. The physiological effects of vitamin D deficiency range from reduced dietary absorption of calcium to a compromised immune system and modified adipose tissue function. The ectodysplasin A receptor (EDAR) gene has a range of pleiotropic effects, including sweat gland density, incisor shoveling, and mammary gland ductal branching. The frequency of the human-specific EDAR V370A allele appears to be uniquely elevated in North and East Asian and New World populations due to a bout of positive selection likely to have occurred circa 20,000 y ago. The dental pleiotropic effects of this allele suggest an even higher occurrence among indigenous people in the Western Hemisphere before European colonization. We hypothesize that selection on EDAR V370A occurred in the Beringian refugium because it increases mammary ductal branching, and thereby may amplify the transfer of critical nutrients in vitamin D-deficient conditions to infants via mothers’ milk. This hypothesized selective context for EDAR V370A was likely intertwined with selection on the fatty acid desaturase (FADS) gene cluster because it is known to modulate lipid profiles transmitted to milk from a vitamin D-rich diet high in omega-3 fatty acids.

The taphonomy of human remains in a glacial environment

A glacial environment is a unique setting that can alter human remains in characteristic ways. This study describes glacial dynamics and how glaciers can be understood as taphonomic agents. Using a case study of human remains recovered from Colony Glacier, Alaska, a glacial taphonomic signature is outlined that includes: (1) movement of remains, (2) dispersal of remains, (3) altered bone margins, (4) splitting of skeletal elements, and (5) extensive soft tissue preservation and adipocere formation. As global glacier area is declining in the current climate, there is the potential for more materials of archaeological and medicolegal significance to be exposed. It is therefore important for the forensic anthropologist to have an idea of the taphonomy in this setting and to be able to differentiate glacial effects from other taphonomic agents.

Dental Morphology in Biodistance Analysis

The applications of dental morphology within biological distance studies in both forensic anthropological and bioarchaeological settings are explored. This review includes a discussion of permanent and deciduous teeth, trait heritability and thresholds, and data collection and analysis. An examination of the major geographic “dental complexes” is also presented, which is followed by a review of dental morphology in forensic anthropology and bioarchaeology. Finally, a consideration of hominin dental morphology is given to provide an evolutionary perspective, which is key to understanding modern human variation. The authors further highlight the importance of studying teeth within biological anthropology as a means to answer questions of anthropological and medicolegal interest.

Dental Metrics in Biodistance Analysis

Abstract The utility of dental metric data in both a forensic anthropological and a bioarchaeological setting is surveyed. This review involves a discussion of data collection methods and statistical treatment, as well as the effects of sex, age, biological stress, and development on tooth size. Heritability rates are also explored, as are general trends in hominin evolution and among modern human populations. The authors highlight the importance of understanding biological data in order to employ appropriate statistical analyses.

Cranial nonmetric and morphoscopic data sets

Abstract Cranial nonmetrics and morphoscopic data are typically used differently by biological anthropologists depending on the context of their research. Bioarchaeologists often use nonmetric trait data to explore patterns of gene flow and genetic isolation in regional contexts. Collectively these are referred to as biological distance studies. Forensic anthropologists usually focus on a set of nonmetric traits, now commonly described as morphoscopic traits, to estimate ancestry in unknown skeletal remains toward the goal of positive identification. In this chapter both types of cranial trait are outlined to include definitions and data collection protocols. Statistical measures of biological distance of data sets within both bioarchaeological and forensic settings are also described.

Northern exposure: Mandibular torus in the Greenlandic Norse and the whole wide world

OBJECTIVES In the first issue of the American Journal of Physical Anthropology, E.A. Hooton noted the expression of Eskimoid characteristics in the Icelandic skull, one of which was mandibular torus. Our goal is to evaluate this trait in another North Atlantic population, the Greenlandic Norse. MATERIALS AND METHODS An investigation of mandibular torus was carried out on all Greenlandic Norse skeletons disinterred up to 1986 (n = 109), along with comparative samples from Iceland (n = 82), Norway (n = 98), and Denmark (n = 64). Torus expression was scored on a six grade scale with absence and five degrees of trait presence. RESULTS Greenlanders and Icelanders show extraordinarily high frequencies (65-97%) and pronounced expressions of mandibular torus. More surprising was the almost complete absence of this trait in a Danish Viking sample (9%) and a significantly lower frequency in medieval Norwegians (48%). DISCUSSION The dramatic expression of mandibular torus in the Greenlandic Norse and their contrast to related Scandinavian populations in Europe stimulated the collection of data from the literature and the database of Christy G. Turner II for 49,970 individuals in 335 populations. When plotted on a global scale, mandibular torus shows a strong clinal distribution with the highest frequencies in northern latitudes and the lowest frequencies around the equator. Although mandibular torus has some hereditary component, as indicated by family studies, the trait has a strong environmental component of variance. How factors of a northern environment, including climatic stress and dietary behavior, influence torus expression remains enigmatic.

Chapter 4 – Advances in Cranial Macromorphoscopic Trait and Dental Morphology Analysis for Ancestry Estimation

Abstract This chapter focuses on the use of cranial macromorphoscopic traits and dental morphology as an important component of the estimation of ancestry. These types of categorical data are now moving into a rigorous statistical framework within forensic anthropology, despite the fact that metric data made this shift several decades ago. The forensic anthropologist now needs to be familiar with these types of categorical data and how they are collected and analyzed. These data, as well as current applications and future avenues of research, are discussed. The chapter concludes with a case study that illustrates how current methods can be used and also demonstrates the classificatory power of these data.