The curvature in the lower back (lumbar lordosis) helps balance
the upper body over the pelvis.
In the upper half of the pelvis, the size, shape and
orientation of the iliac blades differ between apes and humans in a
way that reflects our commitment to striding bipedal
locomotion
Although the ilia are short in length compared to a chimpanzee,
they extend more broadly to the side, resulting in a pelvis that is
very broad overall.
This pelvic width contributes to a very different body shape
for early hominids than for humans.
The width of the pelvis affects the muscular requirements of
walking