The human spine (relative to the great apes) has invaginated ventrally (forward) into the abdominal cavity in order to closely coincide the center of mass with the vertebrae centers of rotation, thereby reducing torsional and bending stresses on the spine and increasing the mechanical moment produced by the erector spinae muscles, thus also assisting in balancing the torso over the interacetabular axis during pregnancy.
Source: wiktionary