Theory:

This fictional story explains how the camel got a hump on his back. The world had just begun, and the animals had started working for humans. An ox, a dog, a horse, and a camel worked for a man. Except for the camel, all three animals worked hard. The camel said "humph" for anything anyone asked him. His duties were divided and reallocated to the three animals by their master.
 
They complained to the Djinn, who was the person-in-charge of the desert. When the Djinn asked the camel, he replied the same "humph". The Djinn puffed up the camel's back with his magical powers, and it was called as the hump since then. The camel could store energy to work, for three days without eating. This was the punishment and the advantage given to the camel for not behaving properly.