Estimating sex from the pelvis
The pelvis is the most sexually dimorphic region of the skeleton. The overall shape of the male pelvis is narrow and steep, and the female pelvis is generally broader, with a larger pelvic outlet to facilitate pregnancy and childbirth. Since this is the only region of the skeleton where there is such a functional difference, the pelvis proves to be the most important bone for determining biological sex. The accuracy of sex determinations from the skeleton based on the pelvis alone is usually placed at around 96%, but this will vary depending on the degree of preservation and fragmentation. In forensic and archaeological contexts the pelvic girdle is often not complete and sex determination relies upon recording and assessing individual sexually dimorphic features as follows.
The male sciatic notch tends to be narrow and ‘U-shaped’ and the female sciatic notch is wider and ‘V-shaped’. In some individuals, the sciatic notch may seem intermediate and difficult to assign as male or female. In such cases, it is useful to refer to the ‘composite arc’.
Three pelves with the sciatic notch highlighted. Male is on the left in red, intermediate in the middle in orange and female on the right in yellow.
If you do have an intermediate sciatic notch, and you’re not sure whether it’s male or female, it’s useful to use the composite arc. Here, you follow the edge of the sciatic notch around the superior surface of the auricular surface. In males, you’ll see that it forms a continuous arc. When you try to do this in females, you’ll see that it misses the superior surface of the auricular surface, and it forms almost two separate arcs.
The composite arc highlighted with the single ‘male’ arc on the left and the ‘female’ double arch on the right. (Extra: Try to find the composite arc on the middle pelvis. Do you think it is male or female?)
This is a depression in the bone surface located inferior to the auricular surface. Both males and females may have a preauricular sulcus, but it is less common in males. The morphology of the sulcus also differs between males and females. In females, it tends to be deeper and to have clearly demarcated edges, whereas in males it is usually shallow with open sides.
In this female pelvis, the preauricular sulcus is highlighted in yellow. Be sure not to confuse the preauricular sulcus with the nearby post-mortem damage (white-coloured depression).
Overall, the features of the female pubic bone tend to be more gracile (light, fine, smooth) and more sharply defined than in males. Male pubic bones are usually thick and more robust.
The angle formed by the ischio-pubic ramus below the pubic symphysis is wider and more ‘U-shaped’ in females than in males. Males have a narrower subpubic angle that tends to be more ‘V-shaped’.
A female subpubic angle is highlighted in yellow and a male subpubic angle is highlighted in red.
Females have a ‘ventral arc’, which is a flattened, roughly triangular-shaped aspect to the ventral (anterior) surface of the pubic symphysis.
Female pubic bones with the ventral arc highlighted on one side.
In females, the iliopubic ramus (part of bone connecting the ilium to the pubic bone) is long relative to the diameter of the acetabulum. In males, the length of the iliopubic ramus and diameter of the acetabulum are often of roughly equivalent dimensions.
A female and male pelvis highlighting the relative length of the pubic bone to the diameter of the acetabulum.
In males, the ilium is narrower and the iliac blade has a more pronounced ‘S-shaped’. In females, the ilium is broader and the ‘S-shaped’ appearance of the iliac crest is shallow.
For a brief summary of these and some additional sexually dimorphic features of the pelvis, please see the table provided below.
Take a look at the annotated 3D models of male and female pelves in the ‘SEE ALSO’ section below this article to practice recognizing and recording the traits used to estimate sex from the pelvis.
In the next step, you’ll be learning how to estimate sex from the skull, which has a different range of features, advantages and limitations.
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