DETERMINATION OF SEX

Pelvis

The pelvis provides the most abundant and accurate data for sex estimation. Differences between males and females are well marked and have been confirmed by considerable research.

Size

The female pelvis is broader, even though the male pelvis may be heavier and more robust.

Sciatic Notch

The sciatic notch (Fig. 68a) is located at the junction between the ilium (upper, flat portion of the pelvis) and the ischium (lower portion of the pelvis). In females, the notch is wide, usually forming an angle of about 60 degrees. In males, it typically is narrower and forms an angle of about 30 degrees.

Auricular Area

The auricular area is the medial portion of the ilium that articulates with the sacrum (Fig. 68a, 92). It tends to be flatter in males than in females.

Pre-auricular Sulcus

This feature is a groove between the auricular area and the sciatic notch (Fig. 68a, 92). It nearly always occurs in females, but seldom in males. If present in males, it is shallower than in females.

Acetabulum

The acetabulum, a socket-like depression on the lateral side of the innominate that holds the head of the femur, is larger in males than in females (Fig. 68b).

Pubis

The pubis is longer in females and the subpubic angle is wider. Both features are correlated with the birth process (Fig. 68b). Three other characteristics are sufficiently distinctive to permit correct identification in 96 percent of the modern specimens examined (Phenice 1969a). These are the ventral arc, the subpubic cavity, and the contour of the medial part of the ischio-pubic ramus.

Cranium

Sex estimates made from the cranium are not as accurate as those based on the pelvis, but they may be useful in the absence of pelvic data. In general, males display larger mastoid processes, larger supra-orbital crests, and larger and more rugged muscle markings, especially on the occipital bone (see Figs. 162-163). Because sex differences in cranial morphology vary slightly among populations, a trained physical anthropologist should be consulted. Such a specialist can identify sex from a cranium with an accuracy of 80 to 90 percent.

Long Bones

Sexual differences in the post-cranial skeleton are well documented, but less consistent than those on the pelvis and cranium. Although the bones of males tend to be larger and more rugged, the accuracy of sex identification is reduced by the overlap between the ranges in males and females in the same population and by the variation among different populations. For example, study of a documented sample may indicate that 95 percent of the femora displaying certain characteristics are from males. This would imply a 95 percent probability that a prehistoric femur with the same characteristics also belonged to a male if sexual differentiation or dimorphism had the same range of variation in the prehistoric and modern populations. This estimate thus includes two potential sources of error: (1) a five percent error resulting from the knowledge that five percent of the modern individuals possessing the characteristic were female, and (2) an error of unknown magnitude introduced by applying data derived from one population to another. Maximum diameters of the heads of the femur, humerus, and radius are fairly good indicators of sex in adults when they fall outside the zone of overlap. Femoral heads with diameters exceeding 48 millimeters are usually male, whereas those measuring less than 43 millimeters are usually female. The maximum vertical diameter of the head of the humerus is usually more than 47 millimeters in males and less than 43 millimeters in females (Dwight 1904-1905, Stewart 1979: 100-101). When the minimum diameter of the head of the radius is 23 millimeters or more, sex is male. When the maximum diameter is 21 millimeters or less, sex is female (Berrizbeitia 1987).

Equations

Discriminant function equations may be used to "calculate" sex. These employ measurements of individuals of known sex to predict the sex of unknown individuals. Because most equations are population specific, care should be taken to select the one that best matches the characteristics of the unknown individual.