The Human Skeleton

The human skeleton is rather different than the skeletons of most mammals. These differences can be attributed to the way we move. Humans are the only mammals who walk predominately on two legs whereas most mammals walk on four. This single difference has led to many adaptations that are characteristically human.

Because we walk on two legs, balance is very important. Our head, shoulders, and hips are positioned directly over our feet. If they weren’t, we would be off balance and would not be able to walk. The lumbar vertebrae, the vertebrae of the lower back, are very broad and heavy because they will support most of our weight. The lumbar vertebrae are not usually as thick and heavy as a human’s.

The angle of our hip joints is different from most mammals because we must keep our legs directly under our body to maintain balance. The angle of the hip joint of chimpanzees, for instance, does not allow them to stand completely upright. Their shoulders and upper body are placed too far forward. Though chimps can stand upright for a short period of time, they typically move on all four limbs.

This habit of walking upright has freed our pectoral limbs for other uses. Other mammals use both of their limbs for walking, running, swimming, or even flying. But because humans only use our pelvic limbs for walking, our pectoral limbs can be used for other important tasks such as using tools. Because humans don’t use our hands for anything besides using tools, our hands are capable of very fine, delicate manipulations.

I could be said that the primary reason why humans have advanced to become the only organisms to leave our home planet is because we began to walk upright. And we were only able to walk upright because of adaptations to our skeleton.