IS THIS PERSON MALE OR FEMALE?
Although in life the differences between males and females are almost always obvious, these differences are not always so apparent, especially when the visual cues of the flesh provides are gone. Males can be up to 20% larger than females, but in some instances, there is little or no difference in size. Many of the quantitative skeletal traits overlap in the middle of the distribution of their values and statistical analysis is required to sort out equivocal examples.
FIGURE 1 The main differences between males and females in the pelvis are due to females’ biological ability to bear children. The most reliable method is the Phenice method, which uses three areas and the presence and absence of certain characteristics.
Sexual differences in the human skeleton begin before birth although they are not truly diagnostic until after puberty. In general, females’ postcranial skeleton develops faster than males and this difference in rate can be used to infer sex in prepubertal indi viduals. Typically, however, sex should not be estimated unless the individual is of an age when puberty has begun; above 18 years of age, sex can be determined with confidence. The significant differences between males and females are size- and function related morphology. The two areas that are used most often to determine the sex of an individual in life are also the most diagnostic in death: the pelvis and the skull. Other bones can be very useful for estimating sex as well, and with only a few measurements, an experienced forensic anthropologist can be accurate 70–90% of the time. The largest number of and most accurate traits for determining sex reside in the pelvis, illustrated in Figure 8.11. The major reason that male and female skeletal anatomy differs so much in the pelvic region is that only females carry and bear babies; human pelvic anatomy reflects this functional difference. Thus, the male pel vis tends to be larger and more robust, whereas the female pelvis is broader and can exhibit pregnancy-specific traits. A useful trait for distinguishing between the male and female pelvis is the sciatic notch, located on the inferior lateral border of the ilium. The sciatic notch is wide (an angle of about 60°) in females and narrow in males (about 30°). A very reliable method for determining the sex from pelvis is the Phenice method, developed by Dr Terrell Phenice in 1969, which uses three characteristics: the ventral arc, the subpubic concavity, and the ischiopubic ramus (see Table 8.2). The ventral arc is a ridge on the anterior surface of the pubic bone that is present in females but absent in males. The subpubic concavity is a depression on the medial border of the ischiopubic ramus, just inferior to the pubic symphysis. The concavity is wider and deeper in females and is only slight, if at all present, in males. Finally, the ischiopubic ramus itself is flatter and thinner in males, whereas in females it is wide and may even have a ridge on it. It is possible to be accurate in sexing a pelvis with only these three traits. The Phenice method cannot be relied upon all by itself, however, because the pelvic remains may be fragmentary and the pubic bone may be absent. Numerous measurements have been used along with statistical analysis to derive more objective sexing methods than descriptive anatomy. Often, these methods are as accurate as morphological traits, but they are important for gauging slight differences between anatomically similar populations.
Table 8.2 Traits Useful for Estimating Sex from the Pelvic bones, Including Those Detailed by Phenice: The Subpubic Angle, the Ventral Arc, and the Ischiopubic Ramus
FIGURE 2 The skull has many indicators of maleness or femaleness on it, but they are not as clear as those on the pelvis. It therefore takes training and experience to become a good judge of variations in populations. A very slender male or a very robust female may have skeletal traits that fall into an overlap between the sexes.
Sex can be estimated from the cranium as well as the pelvis, but the traits may not always be as obvious. As shown in Figure 2, males tend to be larger and have larger muscle attachments than females. The specific areas of interest are the brow ridges, mastoid processes (bony masses just behind the ears for attachment of neck muscles), occipital area at the rear of the skull, upper palate, and the general archi tecture of the skull. The skull is one of the most, if not the most, studied, measured, and examined part of the skeleton. This metric enthusiasm extends to the determination of sex. Thirty-four standard measurements are the minimum for inclusion of a skull into the National Forensic Data Base, and from these, sex (and race, as we’ll see later) can be estimated. These measurements are taken with specialized rulers, called calipers, that are either spreading calipers or sliding calipers. The measurements are taken from various landmarks around the skull. Complicated statistical techniques are used to sort out the measurements, relate them to each other, and then compare them against an appropriate reference population. Software developed at the University of Tennessee, called FORDISC, provides an easy way to analyze and compare data from skeletons, as graphically represented in Figure 8.13. Postcranial bones can also provide information about a person’s sex, but most of this information is based on size and therefore is quantitative. Many of the postcranial bone measurements will yield an accuracy of between 58% and 100%. The measurement may be straightforward, but the interpretation may not be. For example, if the head of the femur is greater than 48 mm, then the person was most likely male; a measurement of less than 43 mm indicates a female. The area between 43 and 48 mm indicates that the size of the person was such that estimating sex from this measurement alone would give an inconclusive result. This example illustrates why it is very important to consider all the recovered bones before making a judgement, and in turn, this emphasizes the need for a comprehensive search and collection of the remains at the scene.
FIGURE 2 This is a plot of the calculations taken from a skull to determine its racial ancestry. The circular areas indicate the range of the populations against which the skull was compared; the skull’s location is shown with an “X.” Given the amount of overlap between some of the circles, it is apparent that even numerical data can sometimes lead to a “fuzzy” answer with race.
