Determining Sex in a Human Skeleton

The fields of forensic anthropology and bioarchaeology are popular among various groups, largely because of their polarized presence on various television shows.  These fields seek to understand who an individual is based on their skeletal and limited soft tissue remains, which make it difficult or impossible for medical examiners or other experts to easily make such identifications.  Forensic anthropologists and bioarchaeologists use a suite of methods to identify individuals, and in today’s blog post a discussion on the optimal methods for identifying sex will be discussed.

The term sex refers to the biological characteristics that establish an individual as either male or female.  There are ideal characteristics, referred to as primary sexual characteristics, associated with being male versus female, such as male have a penis and females having a uterus.  There are also other characteristics, known as secondary sexual characteristics, associated with sex, which can include the presence or absence of breasts/mammary glands and tissues, overall body size, the presence or absence of facial hair, and more.  As previously discussed on the blog we often see a blurring of those ideas in that individuals do not always meet these idealized characterizations and sometimes “men” and “women” share several of these traits to some degree.  Within the fields that focus on skeletal biology there is a recognition of these factors as there is a sliding scale for identifying sex in the skeleton.  This scale ranges numerically on a scale from 1 to 5 with one representing “definitive female” and 5 representing “definitive male” and numbers 2 and 4 designating “likely female” and “like male” respectively.  The number 3 indicates that the skeletal remains are too ambiguous to classify as either male or female.  This does not mean that the individual is devoid of a sex.  It just means that the skeletal remains are not formed in a way that can provide greater insights, which could be the result of damage to the skeletal remains, immaturity of the skeleton (as juveniles and adolescents cannot be accurate assessed for sexual characteristics), or some other factor is at play that obscures analysis.

Figure 1: Sex Differences in the Pelvis

The pelvis and skull are the best skeletal elements to assess for sex of an individual as they provide the most diagnostic evidence.  Generally, women have a wider pelvis than men (note, this is not always the case, particularly in the advent of medical technologies that allow for narrow hipped women to birth children).  When examining the pelvis there are three areas that are examined, which include the pubis, illium, and ischium (Figure 1).  The pubis is examined for the size the ventral arc (or ridge), the depth of the subpubic concavity, and the size of the ischiopubic ramus ridge.  The illium and ischium are examined for the width of the greater sciatic notch, and the illium’s preauricular sulcus is examined based on its size.  Women are typically characterized as having larger sized features as compared to men, meaning the greater the size of these five characteristics the greater the likelihood that the pelvis is that of a female. 

On the other hand, men typically have larger facial features than women (again, we are seeing a trend against this as women are sexually selecting men with finer features), and when examining the cranial features it is expected that males will show more robusticity in the cranium as compared to females.  The skull has several areas that are examined (Figure 2), including those in the face, sizes, and back of the skull.  Characteristics that are focused on include supraorbital margins and ridges (of the eyes), the mental eminence (the chin), mastoid process (behind the ears), and the nuchal crest (of the back of the skull).  Many of these features are actually visible to some extent to the naked eye of living individuals or are accessible through touching (note, please do not touch others without their permission). 

Figure 2: Sex Differences in the Skull

It is with these analyses that information related to sex of an individual as based on their skeletal features can be assessed, which is useful in forensic studies in creating a victim profile and in bioarchaeological studies to create demographic profiles.  Ultimately, these methods are based on idealized standards, and typically no one individual meets all of the idealized qualities.  Case in point, I, a female, have a robust chin that would be scored as more masculine than feminine, but I have a diminutive nuchal crest, which would be scored as definitively female.  The presence of the masculine chin does not negate my status as a female or woman, but it does demonstrate the difficulties in determining sex in skeletal remains.  Ultimately, though, these methods are necessary for the purposes of related study in either forensic or bioarcheological research, and researchers recognize and acknowledge the limitations with these methods and diligently work to hone their individual skills as well as create more refined methods to aid in identification.

Bibliography

Buikstra, J., & Ubelaker, D. H. (1994). Standards for Data Collection from Human Skeletal Remains: Proceedings of a Seminar at the Field Museum of Natural History. Arkansas Archeological Survey.

White, T., & Folkens, P. (2005). The Human Bone Manual. Academic Press.