This program looks at two deserts that are being used as research models in an effort to understand the role of humans in the desert ecosystem. In the Mapimi in northern Mexico, scientists are studying the best methods of irrigation, the disposition of salt in irrigation water, and the introduction of optimum crops where irrigation is possible and of strictly quantified grazing elsewhere. Important knowledge has also been gained from the Mapimi on the effect of rainwater on barren soil and on soil with vegetation. In the desert between Lake Turkana and Mount Marsabi in northern Kenya, scientists are seeking to control desertification caused by overgrazing and over harvesting wood, by identifying the most productive and ecologically nondestructive foods for animals. They are also trying to identify ecologically beneficial adaptations in lifestyle which the nomadic tribespeople would be likely to accept. (28 minutes)