The planet is changing, but pastoralists here in the Sahel region of Africa are in many ways still raising livestock the way their ancestors did centuries ago. As the Sahara Desert encroaches ever southward, the amount of arable land for animals to graze decreases each year. Among them is Amadou Altine Ndiaye, who earlier this year made a 170-kilometer (106-mile) trek in search of more verdant land for animals.