Atlas of Human Cranial Macromorphoscopic Traits

Joseph T. Hefner, Kandus C. Linde

• Éditeur: Academic Press
• Année: 2018
• ISBN:
  9780128143865
• Sujet: Medicina
• Sous-sujet: Ortopedia

Atlas of Human Cranial Macromorphoscopic Traits synthesizes macromorphoscopic traits and their analysis in an accessible manner, providing detailed descriptions and examples of the various character state manifestations intended for use in classrooms, laboratories, and in the field. The volume begins with an outline of the macromorphoscopic dataset, its history, recent modifications to the historical approach, and recent technological and analytical advances. Additional sections cover Nomenclature, Gross Anatomy, Function, Methodology, Line Drawings, Detailed Definitions, Multiple High-resolution Photographs, and Population Variation Data from the Macromorphoscopic Databank (MaMD).

The volume concludes with a chapter outlining the statistical analysis of macromorphoscopic data and a summary of the computer programs and reference databases available to forensic anthropologists for the analysis of these data.

• Provides detailed descriptions, illustrations and high-resolution images of various character state manifestations of seventeen macromorphoscopic traits
• Applies to both forensic and bioarcheological research
• Written by the foremost expert on macromorphoscopic trait analysis and estimation of ancestry in forensic anthropology

Chapter 1

Introduction

Abstract

Few books exist that explore cranial nonmetric traits (sensu stricto) and there are currently none dedicated exclusively to macromorphoscopic trait manifestations. Consequently, the implementation of these slight variations in the cranial form in research and method building exercises has not yet reached the level of maturity needed to enter general acceptance within the biological anthropological community. The introduction of these traits requires some justification. There are many reasons to undertake the publication of a photographic atlas, but perhaps none are more important than recognizing the gap in current knowledge. In order to fill the gap, a unique set of salutary tools and accessible photographs is essential.

Keywords

Macromorphoscopic traits; cranial nonmetric traits; forensic anthropology; EA Hooton; macromorphoscopic databank; human variation; Harvard Blanks

Few books exist that explore cranial nonmetric traits (sensu stricto) and there are currently none dedicated exclusively to macromorphoscopic trait manifestations. Consequently, the implementation of these slight variations in the cranial form in research and method building exercises has not yet reached the level of maturity needed to enter general acceptance within the biological anthropological community. The introduction of these traits requires some justification. There are many reasons to undertake the publication of a photographic atlas, but perhaps none are more important than recognizing the gap in current knowledge. In order to fill the gap, a unique set of salutary tools and accessible photographs is essential.

Much of the earlier work and research on macromorphoscopic traits relied on schematic or semischematic line drawings, which only suggested or hinted at a small part of skeletal reality, often failing to capture the range in the expression for any one character state. In contrast, an atlas using photographic exemplars has the advantage of displaying character states in situ. Proportions and spatial relationships between singular traits and the cranial complex become more exact and they can be more realistically represented. By including multiple examples of the same character state—some idealized and paradigmatic, others slightly anomalous or irregular—the observer will gain a much broader perspective on interindividual variation and should “walk-away” knowing better how to handle idiosyncratic trait manifestations. Photographs correspond more closely to actual observations made in a laboratory or field setting. While line drawings can display similar information, they lack the texture, lighting, and the level of detail observed on actual specimens. When comparing a specimen to these line drawings or orienting a specimen to effectively score a macromorphoscopic trait, photographs provide the necessary landmarks and contextual clues for correct assessments that are frequently missing from line drawings.

In addition, the existing literature on macromorphoscopic trait analysis—and this is especially true of the early, typological trait lists so popular in forensic anthropological literature—focus almost exclusively on how these traits can be used to predict geographic origin (ancestry or “race”) rather than directing the inexperienced to understand the definitions of traits and their individual character states. Consider a similar approach to craniometric analysis. Prior to learning how to successfully implement a discriminant function analysis on a set of measurements, students are first guided through the tedious process of defining the bony landmarks glabella and opisthocranion, how to properly hold the calipers (or digitizing stylus) to measure between those two points, and are made aware of the many pitfalls associated with data collection and recording errors. Grasping these procedures, the student can now learn to use these new-found abilities to estimate biological distances, posterior probabilities, and likelihood estimates of group membership. Students often find confusion in macromorphoscopic trait analysis, where none should exist; however, they have not been treated the same as their metric counterparts. Before learning how to apply these traits to estimates of geographic origin, their manifestations have to be understood. As a result, several texts and research articles must be consulted, each providing some additional knowledge of trait definitions and character state manifestations. The present atlas, however, will portray macromorphoscopic traits with regard to their expression (i.e., character state) and as objects of human variation rather than matters of extreme expression that may not represent the reality of that variation. Hence, the obstacles to better understanding macromorphoscopic traits are removed, while still providing data on the distribution of these traits within and between populations, benefiting both novice and seasoned human skeletal biologists.

Another goal of this atlas is limiting the text to essential components of macromorphoscopic trait analysis and to offer those components didactically in a simple and self-explanatory manner. Each macromorphoscopic trait is addressed equally: nomenclature—designations used to describe the trait drawn from the literature; gross anatomy—important anatomical structures defining the trait; growth and development—increases in size, changes in proportions, and progression toward maturity through increasing complexity of each trait and the gross anatomical structures to which they are associated; functional morphology—relationships between a trait and the function of various structures associated with that trait; within population variation—frequency distribution data within worldwide populations; and character states—anatomically based definitions and line drawings, as well as multiple photographs for each character state.

Finally, pedagogical considerations motivate the presentation of these traits. On one hand, observer experience and a detailed understanding of human skeletal variation drive observational data collection, while on the other hand, considerable debate exists regarding the role expertise should play in scientific endeavors. Consequently, “I’m an expert” can no longer be used (solely) to explain how and why particular conclusions are reached. Ideally, skeletal biology students sit with an expert to learn appropriate data collection methods of macromorphoscopic traits, distinguishing between various nuanced character states and increasing their understanding of the range and distribution of such features. Photographs will never replace the interaction of mentor and mentee working together with a skull in hand, but they do reinforce and support hands-on learning through more realistic demonstrations of variation than line drawings alone can ever capture.

Most of the traits outlined in this volume existed in the literature well-before the macromorphoscopic method was introduced. Many of these traits have a long history in bioarchaeological and forensic anthropological research. To understand that history and the present state of macromorphoscopic data, a short journey into the past is necessary. But first, what are macromorphoscopic traits?

Macromorphoscopic Data and Datasets

Macromorphoscopic traits are quasicontinuous variables of the cranium reflected as soft-tissue differences in living individuals, similar to Brues’ second class of characters which “due to the contour of bone in areas where it closely follows the surface…, are apparent in both [the] skeleton and [the] living” (Brues, 1958:559). Macromorphoscopic traits are subdivided into five classes: (1) bone shape (e.g., nasal bone contour); (2) bony feature morphology (e.g., inferior nasal aperture); (3) suture shape (e.g., zygomaticomaxillary suture); (4) trait presence/absence (e.g., postbregmatic depression); and (5) feature prominence/protrusion (e.g., anterior nasal spine). These traits are typically used to estimate ancestry for the purpose of identification, although their use in biodistance studies is becoming more commonplace.

Historical Ties

In Linnaean Hierarchical terms, macromorphoscopic traits would be considered a subtaxon of traditional cranial nonmetric traits, i.e., nonpathological, slight variations of skeletal elements (Buikstra and Ubelaker, 1994). Macromorphoscopic traits and traditional cranial nonmetric traits are intricately interrelated; not only do they correspond through association by similarity but also through contiguity. Because the terms both belong functionally and structurally to the cranium, the language is occasionally interchangeable. They also share characteristics considered homologs, although any cross-trait functional or structural relationship may be irrelevant. Nevertheless, the historical development of macromorphoscopic traits reflects the development of cranial nonmetric variation.

The five major categories of nonmetric traits in the cranium are: (1) the presence of extra-sutural bone; (2) ossifications and bony bridging; (3) failure of structures to ossify; (4) variation in the expression/manifestation of sutures; and (5) variations in the number and position of foramina. These traits are bilateral and located along the midline. Cranial nonmetric traits include hundreds of traits from the facial skeleton, lateral and posterior vault, and the basilar portion of the cranium, in addition to mandibular and postcranial variations.

The interaction between the genome and the environment in the inheritance and manifestation of cranial nonmetric traits is not well-understood. Regardless, these traits are still used as a measure of relatedness among and between populations due to their correlation to geographic origin and cranial form. Throughout the early 1900s cranial nonmetric traits were thought of as skeletal anomalies worthy of description and naming but of very little analytical value. They only gained a reputation as important contributors to understanding human variation in the 1960s and 1970s. Exploration into the human genome and a deeper understanding of the laws of inheritance led researchers to consciously and more thoroughly explore the use of cranial nonmetric traits in biological distance analysis, kinship studies, and postmarital residence patterns.

E.A. Hooton (1887–1954)—Professor of Physical Anthropology, Harvard—had a keen eye for skeletal variation, and as one of the earliest and certainly one of the most prolific American physical anthropologists, he played an essential role in the reification of cranial nonmetric trait analysis. His work in bioarchaeology, criminal anthropology, and quantitative methods, together with his principal area of research into the nature of “race” and human variation, led to the development of the Harvard Blanks for skeletal analysis. The Harvard Blanks (or occasionally the Harvard List) facilitated data collection on the skeletal variables Hooton assumed useful for differentiating between micro- and pseudoraces of humans. Many of the macromorphoscopic traits used today by forensic anthropologists were included in the Harvard List. Their association with estimations of ancestry is the direct result of Hooton’s influence and pedagogic prowess. Hooton’s students, like their mentor, included those traits—traits such as anterior nasal spine, palate shape, and postbregmatic depression—as possible indicators of Native American ancestry.

As forensic anthropology matured into a firmly established field, the identification of ancestry from skeletal remains drew heavily from these earlier studies. Until recently, however, there was little effort to standardize how macromorphoscopic data were collected and there were no quantitative methods for analyzing the traits in a manner permitting verification and replication.

Macromorphoscopic Data in the Modern Era

The basis of macromorphoscopic trait analysis is the documentation of traits suitable for investigations into relationships among and between populations on the basis of cranial morphology. Whether identifying ancestry for an unknown set of remains, or the identification of biological relatedness in an archeological sample, the traits of interest must be suitable for the construction of classes (groups or individuals). Further generalizations can be made regarding the population from which a sample is drawn. Even though the initial use of these traits was somewhat restricted (i.e., the identification of pseudoraces by Hooton), they pertained to a wider range of meaningful biological generalizations that can be used to estimate ancestry. Hooton recognized their utility. He also recognized the need for refinement, method standardization, and quantitative and qualitative analyses. Even though the collection and interpretation of cranial nonmetric traits were not unusual, the methods were not entirely accepted and very little attention was given to Hooton’s warnings regarding the need for standardization and more directed data collection efforts. Researchers of that era agreed with Hooton’s call for rigor in trait analysis. Unfortunately, there was no effort to standardize the traits beyond written descriptions of extreme trait values or the occasional line drawing displaying one particular trait or another. When data were collected, samples were often too small for meaningful generalizations. Perhaps more damning, some researchers would present only anecdotal impressions of trait manifestations, with no regard to scientific suitability, implications of confirmation bias, or other issues introduced when authoritative statements were made with no empirical support.

A resurgence in validation studies at the end of the 20th century and now into the 21st—for both craniometric and cranial nonmetric analytical methods—led to refinements in all manners of analysis related to the biological profile, including validation studies focusing on ancestry estimation methods. Personal preferences and individual emphases frequently affect trait importance in a visual, heuristic method. These preferences unduly influence trait selection in future work, even though the often post hoc nature of trait selection is not considered. When no clear protocol is developed for a method, no two authorities are likely to adopt the same traits for their analysis: expertise is the sole determinant. Even when the same traits are used, nomenclature aside, the two could arrive at different decisions on how the trait is manifesting or how much importance a trait should be given. Replication and repeatability between observers is one of the hallmarks of good science and required of any researcher worth her salt.

In order to construct a macromorphoscopic approach to estimate ancestry, many of the traits used since Hooton’s day require refinement with standard illustrations, anatomically based definitions (of each trait and each character state), frequency distribution data for large reference samples from around the world, and analytical methods capable of handling categorical data within a classification model.

A fundamental part of method standardization, on any level, is a decrease in overall subjectivity. Standardizing macromorphoscopic trait data collection is essential for data sharing, reference data collection, and, in the end, data analysis on an analytical scale as robust as is currently enjoyed by craniometric analysis. Macromorphoscopic Traits (MMS, v1.6) is a data collection computer program for 17 commonly used macromorphoscopic variables. The purpose of MMS is the standardization of trait data for comparison across populations and for use in the analysis of forensically significant remains. Each trait definition is presented with individual character states and line drawings. All data are stored in a two-part relational database for easy data retrieval. MMS is currently available for researchers.

The Macromorphoscopic Databank

Data collected using the MMS program are eventually stored in the Macromorphoscopic Databank (MaMD)—similar in scope and function to the craniometric data stored in the Forensic Databank. The MaMD currently contains macromorphoscopic trait data for 7500+ individuals comprising over 20 populations from around the world and is also available to interested researchers. All of the data in the MaMD were collected using protocols initially developed at the Smithsonian Institution, Repatriation Laboratory in Washington, DC using software designed specifically for data collection of human skeletal remains (https://osteoware.si.edu/).

The MMS program and the MaMD are simply the beginning. The application of macromorphoscopic trait analysis to questions stemming beyond ancestry estimation in forensic anthropology or biological distance analysis in bioarchaeological settings is countless. The inclusion of prehistoric skeletal collections from the United States and international collections from abroad will answer bigger questions about population variability at finer levels of resolution. In turn, the analysis of secular trends within the United States using macromorphoscopic traits will have a far-reaching effect on how we view variation in this country. Tying these data in with genetic, meteorological, and craniometric samples will potentially address some of the long-standing questions on the epigenetic nature of macromorphoscopic traits. Mixed model approaches have great potential for future efforts to understand human variation as it developed in situ and these same studies are quite promising for exploring the impact of the genome and the environment on trait manifestation.

Cranial Samples

Many skeletal collections were visited and photographed for this atlas. These are described elsewhere (see Preface) in detail; however, several general points on the selection of individuals to include in this volume should be addressed.

First, any volume attempting to present broad geographic skeletal variation will be biased in some way by the selection of appropriate samples. The clinal nature of trait variation precludes categorizing schemata. So...