There are four physiologic curvatures of the spine, including cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis. 1. The physiologic curvature of the cervical spine is forward convex, and cervical spondylosis often results in straightening of the cervical spine. 2. The thoracic spine is convex backward to help accommodate the organs inside the thoracic cavity. 3. The lumbar spine is convex forward to help relieve the cushioning shock of walking upright. 4. The backward convexity of the sacral vertebrae is a sign that humans have evolved from reptiles to walking upright. These four physiological curvatures not only help stabilize the position of internal organs, but also reduce the impact of movement. In children who do not yet walk upright, the four curves are not obvious, but they will appear slowly after they begin to walk.