A type of fatal disease that arose when humans became able to walk on two legs.

herniated disc

Because vertebrates were not evolved to be advantageous for bipedal walking in the first place,

[The structure of the spine is advantageous for receiving gravity horizontally, but the spine receives it vertically, so the force received by gravity is different for each disc.]

Humans have the great advantage of being able to use their hands by walking on two legs, but

As vertebrates, structural limitations arise from bipedal walking.

[In fact, just looking at the robot structure, bipedal walking is an inefficient form. Since robots only need to add more arms, there is no advantage to bipedal walking.]