Due to the evolution of bipedalism in humans, the pelvis had evolved to have a shorter, more forward curved ilium and broader sacrum in order to support ambulating on two legs. This caused the birth canal to shrink and form a more oval shape, thus the infant must undergo specific movements to rotate itself in a certain position to be able to pass through the pelvis. These movements are referred as the “"seven cardinal movements",” which the infant rotates itself at the widest diameter of the pelvis to allow for the narrowest aspect of the fetal body to alight with the narrowest diameter of the pelvic. These movements include engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion.