Chimps and humans have differently structured hips. Whilst still very similar, a chimp hip is significantly flatter and higher than the human pelvis.
A variety of evolutionary pressures have prompted this divergence in hip shape, although the strongest has been each species preferred locomotory method. A chimp pelvis is adapted to quadrupedal knuckle walking, a human pelvis to bipedal locomotion.
Ours is more 3 dimensional, forming a lower platform that can support all of our vertically stacked organs.
Meanwhile a chimp pelvis is designed to provide a rigid structure that locks the body in position. This way its horizontal orientation can be obtained with minimal muscular effort.
The different shape of these structures has some other unusual effects, aside from supporting the body in each species preferred means of moving.
Notably, a chimp pelvis is too high up the body to twist independently of the upper half. Humans, with the lower down hip, can twist their top and bottom halves individually.
Aside from being able to annoy chimps with our unique dances, our ability to twist our hips has some important functional implications.
As we walk our pelvis is constantly rotating and reorientating itself to be in the best position possible at any given moment. This helps maximise efficiency and decrease damage done to our legs.
For example, our pelvis rotates forwards with our leading leg. This is known as “pelvic tilt” and decreases the length it has to travel to reach the ground, reducing the stresses of impact and avoiding trauma.