Sex determination of remains
Sex determination of remains refers to the process used by forensic scientists to ascertain the biological sex of decomposed human bodies. This determination is significant as it helps establish the identity of unknown human remains, leveraging the physiological and anatomical differences observed between males and females. Forensic methods rely on skeletal features, especially the pelvis, which is the most reliable indicator due to its adaptations for childbirth. Other bones, such as the skull and long bones, can also provide insights, though they may yield less accurate results. In cases where skeletal remains are not intact, DNA analysis can be utilized, particularly by identifying sex-specific markers like Barr bodies found in female cells. However, challenges arise in sex determination when remains are badly decomposed, and demographic variations can complicate accurate assessments. The field utilizes both qualitative observations and metric measurements, with advanced software tools aiding in the analysis of skeletal data. Overall, sex determination is a vital initial step in forensic investigations, contributing to a deeper understanding of human identity in the context of legal and historical inquiries.
Sex determination of remains
DEFINITION: Process of discerning the sex of a decomposed human body based on knowledge of the physiological and behavioral differences between the sexes.
SIGNIFICANCE: The sexual dimorphism of human beings allows forensic scientists to accomplish one of the most important initial steps in ascertaining the identity of unknown human remains—the determination of sex.
Male and female human beings exhibit significant anatomical and behavioral differences. For example, male humans are on average larger and stronger than female humans, and female humans gestate, bear, and nurse the young. For forensic investigators, challenges in determining the sex of human remains occur primarily when bodies are badly decomposed. Remaining tissues may contain (deoxyribonucleic acid) that is not too degraded to allow for analysis; in such cases, routine forensic DNA analysis to determine the identity of the remains based on short tandem repeat (STR) markers includes a marker for sex determination such as the one within the gene for dental enamel (amelogenin).
When sufficient skeletal remains are available, forensic scientists may determine sex by using methods that exploit the structural differences associated with muscularity and size in men and with childbearing in women. Teeth are not sufficiently different between the sexes for forensic purposes. Sex differences in skeletal remains are relatively trivial at birth, and using such remains to determine the sex of juveniles is difficult at best. Some early differences between boys and girls do occur in the pelvis, but reliable sex differentiation is not possible until after the anatomical changes associated with puberty. The methods that forensic scientists use to assess sex differences in skeletal remains fall into two categories: anthroposcopic or qualitative characteristics (eyeball) and metric traits (quantification). Metric measures have more influence in court because they allow more accurate specification of degrees of reliability.
Sexually Dimorphic Regions of the Skeleton
For adults, accuracy at determining sex is from 90 to 100 percent with the entire skeleton but declines to 90-95 percent, 80-90 percent, and about 80 percent, respectively, with only the pelvis, only the skull, and only the long bones. The impact of giving birth on the shape of the pelvis makes it the most reliable bone for differentiating the sexes. Most of the sex-specific features reflect how a woman’s pelvis is designed to permit the fetus to exit the woman’s body within the constraints of bipedal walking. The inferior bony pelvis must be angled out of the way, and these pressures result in different morphologies (structures) and angles that for some features, in combination or alone, can be as accurate as 96 percent. The pelvis is also the best bone for use in any attempt to determine the sex of the remains of a juvenile.
The skull is the second most useful structure for determining sex, but some traits vary depending on the ancestral origins of the individual. Some features typical of European-derived female skulls, such as relatively high forehead and smaller size, are shared with some Asian male skulls. Some overlap also exists between male and female skull traits within populations, although typically male skulls are not only larger but also more rugged in appearance. These average differences are partly a function of age. Young male skulls look more feminine because of less developed muscle attachments, and older female skulls can look more masculine after menopause. More reliable is the use of computer software that determines sex based on discriminant function analysis of a series of measures between points on a skull.
Postcranial bones can also be used to determine sex, although with less success. Overlap exists in skeletal characteristics of men and women, less so in the shoulders and feet than in the lower limbs, but, again, measures can vary depending on the population. Differences are dependent in part on genetic differences among ancestral populations and in part on environmental influences, particularly nutrition. Malnourished individuals can be smaller and less muscular than those who are better nourished, so poor nutrition can sometimes increase the overlap between male and female skeletal characteristics, because men are often more sensitive to this kind of stress.
DNA evidence of sex can only be accurately used when the genetic material of the remans has not experienced severe degradation. One method is to test for the presence of Barr bodies, the condensed remains of an X chromosome found in the cells of females. Barr bodies can be found in hair and blood. If a Barr body is detected, then the remains must be female, as males do not possess the chromosome.
Limitations of Metric Methods
Metric methods for determining sex from skeletal remains involve measuring between points on a structure, such as the skull, and then entering the measures into a software program that performs discriminant function analysis and predicts the sex of the unknown individual based on the resulting value. Formulas vary in terms of which measurements are necessary; this provides flexibility in the case of incomplete bones.
The data used in these discriminant function analyses have been generated from skeletal collections for which the sexes of individuals are known; most have been derived from studies on the Hamann-Todd Human Osteological Collection at the Cleveland Museum of Natural History and the Robert J. Terry Anatomical Skeletal Collection at the National Museum of Natural History in Washington, D.C. The specimens in both of these collections were gathered in the Midwest during the first half of the twentieth century; thus the individuals represented experienced diets and disease ecologies significantly different from those of modern Americans. In addition, the collections do not represent the diversity of ancestral origins found in the population of the United States in the twenty-first century.
Because the functions derived from these collections are losing their utility, the University of Tennessee at Knoxville set up the Data Bank in 1986 to centralize the growing amounts of information available on skeletal remains in modern populations. Most forensic anthropologists compare unknown individuals to populations in this database with the help of FORDISC, a forensic anthropology software program.
Bibliography
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Jimenez, Julianna. "The Use of Barr Bodies to Determine Sex in Samples of Forensic Significance." Rutgers University, 6 May 2022, biology.camden.rutgers.edu/biology-day/the-use-of-barr-bodies-to-determine-sex-in-samples-of-forensic-significance-2/. Accessed 16 Aug. 2024.
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