Answer
In he adult human there are four curves in the vertebral column or spine. These are superior to inferior the cervical, the thoracic, the lumbar and the pelvic. These curves are not present of birth. In a newborn infant the spine has a general "C" shape--roughly the shape of the spine of adult monkeys and apes.
Work Step by Step
The cervical curve begins in a crawling infant. It enables him to lift up his head and look forward. The lumber curve takes shape later, as the infant begins to walk. The "S" shape that develops as a result, facilitates bipedal locomotion.
The thoracic and pelvic curves are leftovers; they are parts of the original "C" conformation. Therefore, they are called primary curves. However, the cervical and lumbar curves are new developments and are designated secondary curves.
