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How Can we Tell if a Human Skeleton is Male or Female without the Pelvis?

Evolution has determined that males and females develop using different genetic mechanisms which influence the action of hormones on the body. Females primarily produce estrogen, and in smaller amounts, testosterone. Testosterone is a hormone that makes things grow bigger; in men testosterone is produced on the order of 10 times more than in women. Testosterone, in men, is the major hormone involved in the sexual development of the testes and prostate. It also causes men to grow bigger muscles (Baum and Crespi). The human skeleton also develops as part of the hormone growth-mediated process, with men developing larger skeletons, ostensibly to carry the additional muscles needed for survival and protection of the female and offspring. Females tend to have smaller skeletons more suited to childbearing and childrearing (Liu, Sartor and Nader).

In mammals there are two genders, male and female. Males provide one half of the genetic material through their sperm, and females provide the other needed half of the human genetic material in their eggs. Together, life begins. Males of mammal species do not carry young; that is, they do not become pregnant. Females carry the fertilized embryo to maturity, resulting in live birth of an infant. The female body is evolutionarily designed for this role, having wider pelvic bones to support the growing baby in utero (Silva, Botelho and Prado). The ability to tell females from males when only skeletal material is present can be done by examining the pelvic bones. Female pelvic bones are wider, more horizontally placed, and broader. Male pelvic bones are more vertical, narrower, and less broad. However when the pelvic bones are not present for analysis, other skeletal clues must be ascertained to determine gender (Kim, Sung and Song).

Other parts of the human skeleton can refer to the gender of the person, though the pelvic bones are the best indicator. The skull can also be used to differentiate between genders. The skull of males is generally larger than that of females. The chin tends to be more square in males than females. The brow ridges are larger and broader, and the mastoid projections behind the ears tend to be larger in males. Due to the increased muscle mass of males, there is also a more defined muscle attachment ridge on the back of the skull where neck muscles would attach. Conversely in females the chin is narrower, the skull is smaller, orbital ridges are sharper and narrower, the forehead has a more vertical angle, mastoid processes are smaller, and muscle attachment ridges are less pronounced on the back/base of the skull (Silva, Botelho and Prado).

Other features that tend to differentiate males from females in skeletal analysis are that females have narrower rib cages than men, males have heavier and longer limbs with heavier phalanges, and females tend to have rounder should blades than men do; additionally, females have another maternal feature evidenced in the carrying angle of their forearm, this angle is more pronounced in females than males likely due to the increased child-carrying role of the female (Kim, Sung and Song).

Additional skeletal clues referring to development are that female skeletons tend to mature faster than males, with a hardening of the cartilage occurring at a younger age, by age 18 for females and age 21 for males. This may be due to the reproductive advantage conferred on the species if a female body is strong enough to support a child in utero at an earlier age (Liu, Sartor and Nader).

The age of the skeleton also provides clues relating to development. While younger children and infants may be hard to tell apart in gender, the elderly skeleton may be show osteoporosis in the female skeleton as compared to age-matched males, as the lack of estrogen contributes to decreasing bone density with age. The male skeleton, due to the presence of testosterone, may simply not degenerate as fast in terms of osteoporosis as a female's would (Kim, Sung and Song).