Camels are called the "ships of the desert". Why? well, like ships that carry goods and people across the oceans of the world, camels carry goods and people across the deserts. They are very important to people who live in the deserts. Groups of camels that carry goods are called "trains". Camel trains can be made up of hundreds of camels. There are two types of camels: the dromedary camel or the Arabian camel with a single hump and Bactrian camel with two humps. Camels live between 30 and 50 years and are kept by people as beasts of burden. People keep camels also for their milk and meat. Camel milk is said to be richer in fat and protein than cow milk. Camel meat has been eaten for centries and is still eaten is Somalia, Saudi Arabia, Egypt, Libya, Sudan, Kazakhstan, and other arid regions where camel meat has had a long cultural history. In some regions, camel blood is regarded as a good source of iron, vitamin D, salt, and minerals. For over fifty million years, camels have been evolving. They eventuallly became well adapted to life in the desert. Their feet are suitable for walking on the hot desert sand, and they can live for two weeks without drinking water. Their fur is short and thick to protect them against sunburn and against sandstorms. Also, their long eyelashed keep sand out of their eyes. Camels are well-known for their bad tempers, and they often show their anger by making a loud grunting sound. Nonetheless, they are so important to human survival in the desert that people usually don't mind the bad moods of their camels.