Answer:
It occurred as a result of change to a bipedal stance.
Step-by-step explanation:
Bipedal stance means an organism moves with the help of its two rear limbs. The evolution of humans have been in centuries where they learned to move using their two rear limbs only. It distinguishes humans from four limbed apes. This is by big brains which are used by hominids. The hominids forms the largest part of the brain.