2.6: Estimating Sex and Biological Affinity in the Skull
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Estimating Sex in the Skull
Physical anthropologists are often called upon to identify skeletal remains; this may be for archaeological or forensic remains. Due to substantial individual and populational variation, the reliability of such attempts is rather limited. Moreover, much practice and guidance is required to achieve reliable conclusions. The following is meant to provide only some familiarity with the methods employed.
While virtually all bones display some sexual dimorphism, the pelvis is the most reliable for identification. Using the skull alone is less accurate. In cases of adult crania with which there is neither lower jaw, nor any other part of the skeleton, the diagnosis is about 80 percent reliable. This proportion rises to 90 percent where a well-preserved lower jaw is present; and will reach 96 to 98 percent when a whole skeleton is present. Although there will still remain skeletons which, even though complete, show such ambiguous sexual characteristics that it will be impossible to identify them as either male or female with certainty. The following are cranial traits used in sex assessment:
Overall size – Larger in males; smaller in females.
Muscle attachments – Stronger in males exhibited by roughening; females are generally more smooth overall.
External occipital protuberance – More pronounced in males; rounded and smooth in females.
Forehead – Retreating in males; smooth, round, more vertical and better developed frontal eminences in females.
Glabella – Protrudes in males; smooth in females.
Mastoid process – Large in males; small in females.
Palate – Males are larger and broader; females display less depth.
Supra-mastoid crest – Larger and extend past the external auditory meatus in males.
Supraorbital margins – Rounded and thick in males; sharp and thin in females.
Supraorbital ridges – More pronounced in males; flat and smooth in females.
Zygomatic bones – higher, stouter, and rugged in males.
Zygomatic processes – Heavier in males; more slender in females.
Mental eminence – Square and broad in males; v-shaped and narrow in females. Gonial angle – Less obtuse in males (stouter, rougher, and more everted angles); an angle over 125 degrees suggests female sex.
Estimating Biological Affinity in the Skull
Assessing biological affinity in the skeleton cannot be done with a promise of great accuracy. Nonetheless, legal authorities often wish to have as much information for identification as possible. This is especially true when a burial is found, and it is suspected that the person was the victim of foul play.
Bear in mind that in all populations male skulls tend to be more rugged than females, and that this will complicate the assessment. Also remember that these characteristics are merely typical and not diagnostic, as they may be seen at variable frequencies in all human populations.
The following may be used in assessment of biological affinity:
Australian Aborigine - Long cranium, deep set orbits, well developed brow ridges, pronounced postorbital constriction
San Bushman - Very short face, extremely prominent forehead, gracile skull form
American Indian - Round cranium, nasal overgrowth, shovel-shaped incisors, edge to edge bite, central incisors rotated toward midline, prominent zygomatics, smooth orbits, straight face
American Black - Long cranium, short face, smooth brow ridges, wide nasal aperture, nasal gutter, bregmatic depression, overbite, alveolar prognathism.
Euro-American - Variable cranial shape, variable size, narrow and orthognathic face, nasal sill, narrow nasal aperture, highly angled nasals, overbite, highest frequency of Carabelli’s cusp.