Camels are desert animals, specifically, the deserts of the Arabian Peninsula, North Africa, and the dry mountainous region of Central Asia. Deserts, by definition, are dry, arid intensely hot regions where water is scarce. For an animal to survive in a desert environment, it must have developed physical characteristics that allow it to live in such a region. Water being essential to life, and deserts being devoid of water and very hot during the day, animals that are native to deserts must have mechanisms to keep cool and to survive for long stretches without water.
The most distinctive physical characteristic of a camel is the hump on its back. Once thought to act as a reservoir of water that sustains the camel for long periods in the desert, the hump is actually a mass of fatty tissue that constitutes the major concentration of that essential substance for the animal's body. As the fat metabolizes, it releases water into the camel's body. In addition, the camel's physiology is ideally suited to the desert climate. Its blood cells react in a very specific manner to provide the sustenance of liquid when needed. Camels' body temperatures are also regulated according to the demanding environment in which they live. Similarly, a camel's diet is naturally suited to the types of plants found in deserts.
The longer a camel goes without water, the more its internal mechanisms for survival come into play. The fatty deposit in the hump degrades until it becomes thin and floppy. As the animal feeds and drinks, its fat supply grows and the hump retakes its upright form.