DETERMINATION OF SEX FROM THE SKELETON

• Jurisdiction: Australia

[35.420] Sexing of human skeletal remains is a vital part of forensic identification. Once sex is determined, the possibility of correct identification is immediately increased by 50%.

Sex-distinguishing characteristics of the skeleton are dependent on the existence of sexual dimorphism, which results from the adaptations of the female to the function of childbearing, the influence of sex hormones and cultural differences between the sexes. Although present at all ages, sexual dimorphism becomes most marked after puberty when the secondary sexual characteristics have fully developed. Hence sex can be most readily and most reliably ascertained in skeletons from mature individuals. Senility and pathology may influence sexual characteristics of the skeleton and therefore alter the reliability of sex determination in the aged.

An expert is aware of the range of variation of sexual traits within the skeleton and the degree of overlap that normally exists between males and females. The determination of sex is rarely based on any one skeletal feature alone. Wherever possible, as many criteria as are available are assessed before coming to a definitive conclusion.

The degree of development of sexual characteristics within the skeleton may vary greatly from one racial group to another: Johnson, O'Higgins, Moore and McAndrew (1989). Hence there is a need for awareness of and familiarity with this interracial variation. Because of this, the racial affiliations of skeletal material should be ascertained before the appropriate sexing and ageing criteria are applied.

Visual (morphological) examination remains the quickest and easiest method of determining sex in the great majority of unknown skeletal remains. In experienced hands will result in 95 to 100% accuracy when the whole skeleton is available for assessment.

[35.430] Quantitative metrical methods, where available, should be used to back up the morphological assessment. These metrical methods use statistically determined discriminant functions with sectioning points, above or below which one or other of the two sexes will fall. Their reliability varies depending on the bones assessed but usually lies somewhere between 70 and 95%. The development of discriminant functions based on skeletal measurements has helped greatly in removing the subjective basis from sex determination. Their use tends to back up the morphological assessments made by the expert osteologist and makes reliable sex assessment available to the less experienced. Such functions as are available should be restricted in their application to those population groups from which the functions were originally derived.

The skeletal elements that are of most use in sex determination are listed below in descending order of reliability:

• the pelvis: hip bones and sacrum;
• the cranium;
• the long bones, especially the femur, humerus and tibia; and
• other bones, e.g the sternum, clavicle, calcaneus.

The accuracy of sex determination in adults is stated by Krogman and Iscan (1986, p 259) to be as follows:

entire skeleton 100%

pelvis alone 95%

skull alone 90%

skull and pelvis 98%

long bones 80-90%

long bones and skull 90-95%

long bones and pelvis greater than 95%

In immature (pre-pubertal) skeletons the chances of a correct sex allocation is only 50% unless the pelvis is present, which improves the chances of correct sex allocation...