Outside the womb, the emotional expression made by the baby (i.e. kicking and crying) forms the lumbar curve (a lordosis). The presence of the head, which places a load on the top of the spine develops the cervical curve (another lordosis).
Over time, as the babys movement repertoire grows, the baby develops muscular control over the lumbar and cervical curves, and the curves stabilize.1
Bibliography
1. From M.E. Todd, The Thinking Body, 120-129.

