Sex determination can be accurately assessed through examination of the pelvis and cranium. Using a combination of features is the best way to determine an individuals sex. Due to variations within and between the sexes, single traits may not always be representative of the sex of the individual. Therefore, it is best to use multiple features in determining sex. However, with the limited amount of material that is often found in archaeological digs and forensic cases, this is not always possible.
The pelvis is the most reliable indicator of sex. The birth canal is mostly responsible for the morphological differences seen in males and females. In females the pelvic inlet is wider and more open than in males and the lower sacral vertebrae and coccyx do not curve under as they do in males. These features ensure that the birth canal is wide enough for the passage of an infant.
Greater Sciatic Notch
The greater sciatic notch is a rounded arch located on the ilia, anterior from the auricular surface. Males tend to have narrow sciatic notch, while females usually exhibit a wide notch. A simple test, to determine sex it to places one’s thumb in the greater sciatic notch. If there is room to move one’s thumb from side to side then the pelvis came from a female individual. However, if the thumb cannot move with the arch then the pelvis came from a male individual.
Subpubic concavity is also a good indicator of sex. The subpubic region is located on the pubis, inferiorly to the obturator foramen. In females, the subpubic region is concave, while in males the subpubic region is either straight or convex.
The subpubic angle is the final way to sex an individual using the pelvis. In general, females have longer pubic bones and wider subpubic angles than males. The subpubic angle is a triangular space created by the ramuses of the left and right and ishium and the pubic symphysis, which marks the apex of the triangle. The size angle between the two ramuses can generally be used to determine the sex of the individual under study. In males the subpubic angle is typically less than 90 degrees, while females generally exhibit a subpubic angles greater than 90 degrees.
Femoral head diameter has not proven to be a reliable indicator of sex across diverse, or ancestral populations, but can be fairly accurate when working within a single population. The femoral head diameter is a measure from the most superior point of the femoral head to the most inferior point.
Measurements below 41.5mm indicate that an individual is a female and measurements above 45.5mm indicate the individual is a male.
Measurements between 41.5-43.5mm, tending to be female, and 44.5-45.5mm, tending to be male, are less definite and sex should not be assigned without other strong indicators. Measurements between 43.5-44.5mm cannot give any reliable information about sex.
Cranial morphology is another way of determining sex, although cranial indicators should always be used in addition to pelvic features. For example, it is possible for a male to have a gracile chin, which would leave an abserver to conclude the oposite sex without further examination of additional features.
Cranial morphology varies drastically between populations and therefore, is not comparable in accuracy to the pelvis. Typically, males have more robust features than females because of their larger muscles and overall larger body size. Each indicator should be ranked on a five-point sale, 1 being most gracile and 5 being the most robust. Five features on the cranium can be used for sex determination:
- Nuchal crest
- Mastoid process
- Supraorbital margin
- Mental eminence