A zone of arid and semi-arid country stretches from the Atlantic through northern Africa and the Middle East into Central Asia and India. Besides the Sahara and the Arabian and Iranian deserts it includes vast areas which although not totally barren are subject to low and unreliable rainfall. They include parts of the Fertile Crescent where economies based on the domestication of grains and animals first developed in the Middle East, and they have contained the sites of significant human activity since the earliest times. But as a result their appearance and composition have changed, and they have recently become the subject of serious controversy on a global scale: ecologists see a long-term trend towards the final desertification of these lands, but although they can formulate technical management programs to stem or reverse the trend, the local populations cannot always be persuaded to implement them.