What shape is the spine of modern humans?

The spine of modern humans is S-shaped, which is an important adaptation for bipedal locomotion. This distinctive curvature plays a crucial role in balancing the weight of the head and upper body over the hips and legs, allowing for efficient movement and support. The curves of the spine help to absorb shock and reduce stress on the vertebrae during activities such as walking and running, contributing to overall stability and posture.

In contrast to an S-shaped spine, a C-shaped spine lacks the necessary curves and is typically found in some quadrupedal animals, which have different structural requirements for their mode of locomotion. A straight spine does not provide the same benefits of shock absorption and biomechanical efficiency. Thus, the S-shape is a critical evolutionary feature that reflects the unique skeletal adaptations of humans for a bipedal lifestyle.