Final answer:
Primary spinal curvatures, present from birth, are the thoracic and sacrococcygeal curves, while secondary curvatures, which include the cervical and lumbar curves, develop postnatally as a child achieves certain developmental milestones.
Step-by-step explanation:
The primary curvatures of the vertebral column are the thoracic and sacrococcygeal curves which are remnants of the original fetal curvature. These are present at birth and form the general C-shape of the newborn's spine. Secondary curvatures, which develop after the time of birth, are the cervical and lumbar curves. These curves form as developmental milestones, such as holding the head up and walking, are achieved. The cervical curve forms as the infant begins to lift and hold up the head while sitting, and the lumbar curve develops as the child starts to stand and walk. Both sets of curvatures enhance the spinal column’s strength, flexibility, and capacity to absorb shock, adapting to increased loads, such as when carrying a heavy backpack, and returning to normal when the weight is removed.