Final answer:
The human spine has two lordotic curves, located in the cervical and lumbar regions, and two kyphotic curves, found in the thoracic and sacral regions.
Step-by-step explanation:
There are two lordotic (posteriorly facing) curves in the human spine and two kyphotic (anteriorly facing) curves.
The lordotic curves are found in the cervical and lumbar regions of the spine. The cervical curve, a secondary curve of the vertebral column, is posteriorly concave and allows for the head to be balanced on the neck. The lumbar curve, another secondary curve, is also posteriorly concave and facilitates standing and walking by balancing the weight of the upper body over the lower limbs.
Contrastingly, kyphotic curves occur in the thoracic and sacral regions. The thoracic curve is anteriorly convex and accommodates the thoracic organs while providing attachment points for the ribs. Similarly, the sacral curve is anteriorly convex, but it stabilizes the body and supports the weight of the upper body while sitting.