Which organ supplies a human's bloodstream with oxygen from the air, which can then be taken through the blood to the muscle cells of the arm?

Like the skull, the pelvis is highly useful for determining a skeleton’s biological sex. A wide pelvis is beneficial for child birth, however a narrow pelvis is beneficial for locomotion when walking upright. These conflicting demands are often termed the obstetrical dilemma.

The female pelvis has evolved to its maximum width for childbirth—a wider pelvis would make women unable to walk. In contrast, human male pelvis are not constrained by the need to give birth and therefore are optimized for bipedal locomotion.

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