From Skeletons on the Zahara: A True Story of Survival, by Dean King (Little, Brown, 2004), Kindle pp. 127-128:
The nomads owed much to the Arabian camel. By the time their Sanhaja ancestors had acquired the peculiar humped beasts from the east—between the first and fourth centuries A.D.—desertification had long since intensified, clustering people around oases, where they could grow food. As the land grew more arid and infertile, the black tribes migrated south, while the Sanhaja adapted to nomadic life with the camels, living like bedouins long before the first wave of bedouins arrived. Though not considered ruminants, camels, with their complex, three-compartmented stomachs, regurgitate and rechew their forage, turning poor vegetation into protein and energy even better than ruminants do. It was the camel, which could convert scrub brush into nutrient-rich milk, that allowed the Sanhaja to stay on the desert.
Oddly enough, camelids originated not in Africa but in North America. During the Pleistocene epoch, the ancestors of the llama, alpaca, vicuña, and guanaco migrated south to South America, while the ancestors of the camel crossed an erstwhile land bridge at what is now the Bering Strait to Asia. As the camelids were dying out in North America, camels migrated across Eastern Europe, the Middle East, and North Africa. By 3000 B.C., however, wild camels had become extinct in North Africa too. They were reintroduced on the Sahara as desertification increased their utility there, and they quickly became the most important thing a man could own. He who mastered the camel mastered the land.