Men and women are different in many ways, and much of this is programmed into every cell in our bodies according to our chromosomal makeup (generally XX for female and XY for males). One of the ways these differences in DNA affect growth and development in humans is in skeletal structure. The anatomy of the male skeletal system, including all bones and cartilage, is slightly different from that of females, but these differences are very important for the survival of the human species.
How is the male skeletal system different from females?
There are two main reasons behind the differences between male and female skeletons: first is the time it takes to reach maturity, and the second is accommodations for pregnancy and childbirth. Men’s bones continue to grow and develop, on average, about three years longer than women’s, reaching maturity at around age 21 compared to 18 in women. The result of this is that the bones in a male skeleton are typically larger, thicker, and more dense than those of a female skeleton. It also tends to amplify certain surface features, causing a larger joint surface area in men than women, for example. This also explains why men often have stronger facial features, such as jaw line and brow bone.
Men have much lower levels of estrogen (the female sex hormone) in their bodies than women do, and this causes important differences in the skeletal system which relate to gestation and birth. Since men’s bodies do not have to accommodate a growing fetus during pregnancy, the bones of their lower back (sacrum and coccyx) tend to be longer, less flexible and with more pronounced curvature. And since they will never have to push a baby through their pelvis, the pelvic opening is narrower in men than in women and the pelvic cavity overall is less spacious, the bones are longer and heavier and less rounded.
Is it true that men have fewer ribs than women?
A popular Bible story has led to the widespread misbelief that men have one rib less than women (because the first woman was created from a rib of the first man, as the story goes). However, there is no scientific truth to this. There may be variations in the number of pairs of ribs from individual to individual, both men and women usually have 12 pairs of ribs. The 11th and 12th pairs are not directly attached to the sternum and are called floating ribs; this is generally where variations in the number of ribs are seen, but this is unrelated to the person’s sex.
What is true, however, is that men’s ribcages tend to be larger than women’s. This is because higher levels of testosterone during puberty causes the rib cage to expand to facilitate breathing larger volumes of oxygen.
There are more similarities between the anatomy of the male skeletal system and that of females, although the differences in size and shape of the pelvis are usually sufficient to determine the sex of an individual from their skeleton alone.