Why do camels have humps?

Contrary to popular belief, a camel hump does not hold water; it is a large deposit of fat that can weigh up to 36 kg. When food is scarce, the camel metabolises this fat for energy, and the process even releases some water as a by-product. Storing fat in one place rather than all over the body also helps the camel stay cool, because a fatty layer across the whole body would trap heat in the desert. When a camel uses up its fat reserves, the hump shrinks and flops to one side until it is rebuilt by eating. Camels survive without drinking for long periods thanks to other adaptations, such as oval-shaped blood cells and highly efficient kidneys, not the hump.