Investigations in Sex Estimation

An Analysis of Methods Used for Assessment

Donna L. Harrison

• Publisher: Academic Press
• Year: 2018
• Print ISBN: 9780128157787
• eBook ISBN: 9780128162170
• Topic: Law
• Subtopic: Forensic Science
• Index: Law

Investigations in Sex Estimation: A Comparison of Morphological and Metrical Methods is a collective comparison of the many morphological and metric methods currently used on adult and juvenile human remains. This single comprehensive resource for sex estimation in skeletal material includes discussion on the evolution of sexual dimorphism in modern humans, how sexual dimorphism manifests itself in those bones, the growth development in juveniles and how sexual dimorphism can be measured in their bones. Data is presented which contradicts previously held postulates and some different uses of sex estimation methods are suggested, such as using the grading system to assess evolutionary change in skeletons or grouping juveniles into smaller groups by age to better estimate sex. New insights are offered for future research from the presentation of case studies on gender and a comparison of the sex differences between two African-American collections which suggests a correlation between occupation and evolutionary change. To achieve the objective, data on 294 adults from four diverse collections of known sex are obtained using a total of 67 morphological and metric methods. An additional 23 morphological and metric methods used on juveniles, aged 0 to 18, from two of the collections. The methods are specific to either the cranium, mandible, pelvis, humerus or femur. The compilation of assessment of sex provides definitive answers on which type of method, morphological or metric, is more accurate, which morphological and metric methods are the most accurate, and which bones are more reliable to estimate sex especially in the absence of a pelvis. Investigations in Sex Estimation is intended to be used in the field and the laboratory for the identification of sex in human remains and aims to provide a wealth of data for future research in sexual dimorphic studies.- Provides the anthropological community with the results of the first collective comparison of the many morphological and metric methods currently used on adults and juveniles- Introduces methods, reviews sexual dimorphism, and shares new insights for future research- Highly illustrated, using testing data from four very diverse skeletal collections

Chapter 1

Introduction

Abstract

This chapter offers a brief review of the historical attitudes and issues surrounding the discipline of sex estimation. There are currently many methods used in the field when estimating sex. Morphological methods are methods of observation which are used on areas of the skeleton that are sexually dimorphic. Metric methods are used to measure the differences between males and females to perform statistical analysis. Both types are used in the research and are discussed. Concepts of gender, ethnicity, and culture are also explored as they can have an impact on any study, such as affecting the observer’s assessment of sex.

Keywords

Sex estimation; methods; gender; ethnicity; culture

The determination of sex is a matter of first importance in all anthropological work if reliable records are to be made or accurate deductions drawn from the material employed.

Douglas E. Derry, 1909 (p. 266)

1.1 Overview

The identification of sex in skeletal material is one of the fundamental components necessary for any archeological study. Without knowing the “true” sex—the ipso facto biological sex—of each skeleton, data that is collected and analyzed can be subject to bias and misinterpretation (Cox, 1995; Harrington & Blakely, 1995; Stewart, 1954; Walker, 2005; Walrath, Turner, & Bruzek, 2004; Weiss, 1972). While known sex collections often reduce these errors, many collections are not documented well, if at all, with regard to the sex of the skeletal material; this limitation does not make it any less important to establish sex in these collections.

Sex estimation, along with age estimation, is vital for accurate statistical analysis as well as an accurate demographic interpretation of population data. Compounding the problem is the challenge of estimating sex differences between human males and females which are not as pronounced as they are in other primates. For instance, bone size is highly sexually dimorphic in gorillas as is canine teeth size in chimpanzees (White & Folkens, 2005). By contrast, sex differences in bone size and canine teeth are relatively small in humans. One suggestion is that the only way to establish a high degree of accuracy when sexing human skeletons is to seriate the population; the females will be smaller and the males larger (Ferembach, Schwidetzky, & Stoukal, 1980). While this technique may have some merit, it is not always applicable and raises other questions: just how many are needed in a series in order to accurately determine sex, and how would serialization compensate for the variability inherent in both sexes?

There are other oversimplifications made with regard to sex estimation that do not consider the effect of external factors on skeletal material. For example, sex estimation is more accurate when maturity is reached (Krogman & Iscan, 1986). However, this postulate discounts factors such as diseases or nutritional deficiencies which can affect bone growth during early childhood. Another oversimplification is that the more robust, the more likely the skeleton is considered male; conversely, the more gracile, the more likely the skeleton is considered female (White & Folkens, 2005). This postulate discounts the variability that can exist within populations as well as the effects of age, disease, or nutritional factors on size and growth.

The prevalent view in the literature is that sexual traits do not appear in the skeleton until the age of puberty, usually around 15–18 years of age. Remains before 15 years of age have a 50/50 chance of being correctly sexed (Krogman & Iscan, 1986). This postulate provides an easy excuse to avoid the difficult, but not impossible, task of finding accurate methods for sexing juveniles. For example, Molleson, Cruse, and Mays (1998) introduced a method using the shape of the orbit and reported an accuracy of 89%. As early as 1980, Weaver introduced a method using the auricular surface elevation of the pelvis reporting 85.1% accuracy in males, but only 57.6% in females. The method was retested by Sutter (2003) who produced an overall 71.7%. While these figures may not be as accurate as some adult methods, the results are still better than the 50/50 chance method generally prescribed in the literature.

Estimating sex has inherent difficulties built into what should be a simple process. Foremost is the unintentional bias in favor of males when interpreting the degree of sexual expression. Weiss (1972) performed an extensive study looking at male bias in 43 populations whose sex was unknown; they consisted of Amerindians, Africans, Japanese, and Europeans. These populations covered various time ranges and cultures. He found that 33 of the populations studied contained 39%–80% more males than females; in a random sample, one would normally expect a 50/50 split. Testing these results further to determine if male bias was a factor, he then studied 31 preindustrial populations in which sex was known and verified by records. In this group, only 13 populations had more males. He concluded from the results that in any unknown sex population under study, classification of males will be on average 12% higher than females. His recommendation was to use “population” methods or methods that had been previously used on a related population. However, even this suggestion does not fully solve the complexities of sex estimation. Sexual dimorphism can vary between populations and be affected by growth changes as a result of environmental and nutritional factors (Buikstra & Ubelaker, 1994). Therefore, while two populations can have similar characteristics, the expression of these characteristics can be different.

Other difficulties in estimating sex arise from material that is fragmented and poorly preserved. For example, it is estimated that 30% of the pelves in any archeological sample are missing the pubic bone (Waldron, 1987). When this crucial component of the pelvis, the bone considered the most sexually dimorphic in the literature, is missing or incomplete sex estimation must be able to analyze other bones that are fully present. Additionally, poor preservation of skeletal material can result in a loss of certain age groups for study, such as juveniles and the elderly due to lower bone mass levels; in the former, the bone mass is building up but is still at low levels, and in the latter, bone mass is decreasing as a result of the ageing process. The end result is that often times only the middle-aged group, from 20 to 50, is present (Walker, 1995). Therefore, it is paramount to the researcher to have many tried and tested methods on a variety of bones to estimate sex which can be used on incomplete or poorly preserved skeletons.

1.2 Method

There are currently many methods in the field that are used to estimate sex ranging from simple observations to more complex statistical analysis; each method has its advocates and its critics. What they have in common is the objective of providing accurate data that can then be used to identify, e.g., population trends or ethnic variation. The more information that is available, the more comparative studies can be performed (Brothwell & Zakrzewski, 2004).

The simplest and quickest method to estimate sex is by observation; sexual characteristics in an area of bone are either present or absent, highly marked or minimally marked, or not clear enough to make a judgment. This method, known as the morphological method, is used today primarily on the pelvis, the cranium, the mandible, and some long bones. During the 19th century, as anatomists dissected and examined the bones of the human body, they noticed differences between males and females. For example, Derry (1909) an anatomist working at the Cairo Government School of Medicine in Egypt, published a paper on his research which examined four characteristics of the pelvis that seemed to exhibit distinctive sex differences. These were the iliac crest, greater sciatic notch, subpubic angle and preauricular groove. According to Derry, these features could be recognized at a glance with little effort.

Metric methods also have their roots in the 19th century. Some of the early studies attempted to record and understand how measured differences between males and females could be interpreted and used as a general rule of thumb applied to all human skeletons without regard to population affiliation. For example, Joseph Hyrtl (1871), an Austrian anatomist, studied the differences in sternum measurement between males and females. He concluded that there existed a proportional size difference in the sternum that clearly demonstrated sexual dimorphism. He stated that in females, the manubrium exceeded half the body length while in males, the body length was twice the length of the manubrium. This was later refuted by Dwight (1881) who repeated the study and found that while statistically the mean of his measurements did agree with Hyrtl’s law, individually the measurements did not. In fact, approximately one-half of the skeletons were exceptions to the law. Undeterred, metric measurements still continued to be recorded and analyzed by most anatomists well into the 20th century, most notably by the German anthropologist Rudolf Martin (1928). The second volume of his book was a compendium of measurement instructions for the body, many of which are still referred to and used today. Martin believed that measurements were critical to the study of variation within the human body, both individually and as part of the individual’s population affiliation.

The latter half of the 20th century has seen the introduction of statistical analysis incorporated into anthropological studies; metric data is not just compared, but subjected to correlation testing and fitted into data curves to demonstrate statistical acceptance. While the results may be more accurate when applied to sex estimation studies, accuracy is only as certain as the accuracy of the data being analyzed. If “true” sex is not known, then statistical analysis is subject to the same observational error as either morphological or metric methods. The use of statistical analysis has been questioned by several authors, including Howells (1966). Krogman and Iscan note that “elaborate statistical analysis does not raise the averages appreciably” (1986, p. 259).

In any study that uses a method or methods to estimate sex, the concepts of gender, culture, and ethnicity must also be considered. Specifically, how much of an impact do they have on any given research?

1.3 Gender

Biologically, we are born to be either male or female; we are taught that chromosomes determine biological sex and the resulting development of sexual characteristics. The typical male has a chromosome configuration of “XY” that results in the creation of a scrotal sac containing the testes and a penis while the typical female has an “XX” chromosome configuration that results in the creation of a vagina and clitoris. The term gender used to express one’s own psychosexual concept is a construct of the 20th century; an individual perceives themselves as being either male or female regardless of their external sexual organs. Normally, there is agreement between the mind’s concept and the physical presentation; sometimes there is disagreement. When this happens, difficulties can arise for the individual, especially when they do not conform to cultural norms. Additionally, children can be born with a mixture of external sexual characteristics. For instance, the chromosome can be “XX” but a penis and scrotum are present; similarly, the chromosome can by “XY” but large breasts develop. Individuals who experienced this sexual ambiguity were historically labeled hermaphrodites. Today, they are labeled “intersex” and their condition is known as DSD, or disorders of sexual development (Fausto-Sterling, 2012). These individuals are usually seen by a multidisciplinary team consisting of specialists trained in the latest surgical advances, as well as psychiatrists who provide information, counseling, and support. Often decisions concerning surgery are deferred until such time as the child is old enough to decide for themselves what their psychological gender is (Me, My Sex, and I, BBC, 2011).

This practice was not always the approach taken. In the 1960s and 1970s, the treatment for children who were diagnosed with any kind of sexual abnormality was often surgical alteration depending on how their sexual organs appeared and regardless of how their internal sexual structure was formed. Dr. Money, a renowned sexologist working out of Johns Hopkins University, dominated the field with his views that children were born gender neutral and remained so up to 2 years of age (Money & Ehrhardt, 1972). He was an advocate of “nurture over nature”; the primary factor in determining one’s own gender was not biology but the way in which a child was raised. He devoutly believed that through surgery and hormonal treatment an intersex child could be made into whichever sex seemed best and could be raised as such with no detriment to their mental wellbeing. His most famous case concerned a twin boy, David Reimer, who as an infant of 8 months underwent a circumcision that resulted in the total loss of his penis. When the boy’s parents sought Dr. Money’s counsel, he was given the opportunity to prove his radical new theory by changing the gender identity of a perfectly normal boy. He convinced the child’s parents that the baby boy would be best served by his treatment program, and for the next 12 years, the baby boy was raised as a girl while his twin was raised as a boy. It was the perfect controlled experiment. Dr. Money reported no problems, claiming his treatment a huge success, and published his results in 1972 in his book “Man & Woman Boy & Girl.” He was proclaimed a pioneer in gender transformations by the medical community which resulted in his approach becoming standard practice when treating intersex children (Colapinto, 2000).

However, there were some persons in the medical field who disagreed with his positive prognosis. One of them was Dr. Keith Sigmundson, chief psychiatrist at the Child Guidance Clinic Winnipeg, Canada, currently in charge of the ‘now’ girl’s case. While attempting to continue with the treatment advocated by Dr. Money, he did not fail to notice how characteristically “male” the child acted and behaved (Colapinto, 2000). Another was Dr. Milton Diamond, Professor of anatomy and reproductive biology at the University of Hawaii at Manoa. His early experiments while at university involved manipulating the hormones in guinea pig fetuses. He injected testosterone into the mother; after birth, the females in the litter emulated masculine behavior (Diamond & Young, 1963). The experiment demonstrated that sex was determined before birth while still in the womb; it was nature, not nurture, that determined gender identity. The results prompted him to investigate cases involving gender surgery...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Foreword
• Acknowledgments
• Abbreviations
• Chapter 1. Introduction
• Chapter 2. Background in Adult Sexual Dimorphism
• Chapter 3. Background in Juvenile Sexual Dimorphism
• Chapter 4. Skeletal Collections
• Chapter 5. Methods
• Chapter 6. Pilot Studies
• Chapter 7. Main Study—Luis Lopes Skeletal Collection
• Chapter 8. Main Study—Terry Collection
• Chapter 9. Main Study—Hamann-Todd Osteological Collection
• Chapter 10. Discussion
• Chapter 11. Conclusion
• Photograph Index
• Recording Forms
• Bibliography
• Index