Robert Jones

By: Robert C. Jones

Many of us have probably had an experience of glancing at someone and not being quite certain whether the person was male or female. In view of some of the hair and clothing styles of the last few decades, that has probably not been a particularly rare event.

If you were a medical examiner and were examining an unclothed body, there would be a number of unmistakable physical characteristics that would readily indicate the body’s gender. But what if you had to determine the sex of a body that had been reduced to a skeleton? If there were remains that retained DNA, you could check for the presence of exclusively male, y chromosomes. But what if there were only bones and no usable DNA?

There would still be sexual dimorphism to provide useful evidence. Sexual dimorphism refers to prominent differences between the sexes, the differences being exclusive of reproductive adaptations. An exception to this, especially in female bodies, is that such differences are not usually very prominent in skeletons of bodies of persons that did not reached adulthood.

A general rule in skeletal comparisons is that male bones are, with inevitable exceptions, larger than counterpart female bones. The larger bones of males typically accommodate the attachment and support of larger and heavier muscles. As I noted in a previous essay, male teeth are also somewhat larger than female teeth, but the difference is usually insufficient to guarantee accurate sex identification from them or from their bite marks.

The richest pay dirt, sex-determination-wise, is to be found in bones of the pelvis. As viewed from the front, the pelvic bones define a shape somewhat akin to that of a bowl. The lowest members of the pelvis are a laterally disposed pair of pubic bones that come together in front to border an inverted, V-shaped space. The angle, known as a subpubic angle, of the V reflects the fact that, in a female, room must be provided through which a newborn must pass. Nature typically provides an angle of 100 degrees or more in anticipation of such an event. Males have no apparent need for a large angle and make do with a narrower subpubic angle, typically one of less than 90 degrees.

Sharing a similar child-birthing relationship with the subpubic angle in a female, a centrally located pelvic inlet, through which a newborn must also pass, in the pelvic bones of a female is typically wider than that of a male. The pelvic bones of a female are also usually wider, rounder and lighter than those in the pelvic bones of a male. The size of the pelvic inlet not only reflects the sex of a body; but, because the inlet widens during the birth of a child and does not subsequently contract quite to its former size, it also provides the additional information that the female has given birth.

While on the subject of the pelvis, we might as well take notice of the fact that the sockets (acetabula) in the pelvis into which the heads of thigh bones (femurs) are received, are, since male thigh bones are typically larger than female thigh bones, also larger in males.

More sexual differences are to be found in skulls. A male forehead slants backwardly, and a female forehead is somewhat rounded. Males have more squared chins, and female chins are more pointed. Males unopposedly take the prize for brow ridges Females typically have none.

Taken individually, the foregoing facts do not absolutely prove the sex of a skeleton. Taken collectively, however, such facts can sum to construct an opinion backed by a high degree of certainty.

Extra facts:

The sexual difference in subpubic angles is observed not only in humans but in all known species having womb-based births.

Many persons think that bone is formed of nonliving material. That is only partially true. They also comprise bone cells, fat cells and blood vessels; and they break down and restore themselves as dictated by demands on our bodies.

Bones not only support us, protect our innards and provide useful levers for moving ourselves and other objects; they also store calcium, which must be maintained at a specific concentration in our blood. Red blood cells, some white blood cells and blood platelets, the latter forming clots to keep us from bleeding to death when injured, are formed in a soft core known as marrow in our bones.

The skeletons of newborns are initially formed of cartilage; and their soft cartilage skull plates are not joined. This allows their skulls to deform as they pass through birth canals. By the time all bones are fused, the more than 300 infant bones form only 206 adult bones.

After attaining adulthood, our bones begin to break down at a rate that is faster than they restore, which is why we must maintain a good diet and exercise program, which promote bone growth.