Final answer:
The lumbar curve is the spinal curvature associated with the lower back, developing when a baby starts to stand and walk.
Step-by-step explanation:
The spinal curvature associated with the lower back, which appears when a baby begins to walk, is the lumbar curve. Initially, a baby's spine has a single curve, which is concave anteriorly. This is known as the primary curve. As a baby develops and begins to sit and walk, secondary curves develop, which are concave posteriorly.
The cervical curve develops as an infant starts to hold up their head, and the lumbar curve appears as the child stands and walks. These secondary curves are necessary for proper weight distribution and balance. In adults, the lumbar curve provides greater depth in females.