In the fifth century B.C., Herodotus reported that there had been a time when a person could walk across North Africa from the Atlantic to the Indian Ocean and be always in the shade of trees. No more: the land was well on the way to becoming the desert we know today. Herodotus generalized: "Man stalks across the landscape, and deserts follow in his footsteps." In the tenth century A.D., a Samanid prince identified four earthly paradises: the regions of Samarkand, southern Persia, southern Iraq, and Damascus. No one who has visited any of these sites now would dream of calling it a paradise. They have been cursed with wars, but warfare is only a secondary cause of their degradation. Throughout history human exploitation of the earth has produced this progression: colonize—destroy—move on. When the Pollyannas write history they focus only on the first of these three actions, the desirable effects of which were most evident during the rapid colonization of the New World. In 1845 a now obscure American journalist coined a deathless phrase when he spoke of "the fulfillment of our manifest destiny to overspread the continent allotted by Providence." "Manifest destiny" is one of those catchphrases we love. We would not welcome the words of a journalist who identified colonization as but a prelude to destruction and abandonment. The restless "moving on" of the human species has depended on always having fresh land to move to. Optimists are not easily frightened by the results, of course: as late as 1980 one Pollyanna brightly explained how all turned out for the best in this best of all possible worlds: "Each year deserts the world over engulf an area the size of Massachusetts. A great deal of land lost is agricultural. . . . Fortunately, however, land is always being replaced or coming under cultivation to make up for land lost." An ecologist—ever guided by the question "And then what?"—would insist on a clarification of the above quotation: Does "always" mean "forever"? If so, it implies that there are no limits to earthly space. It is not surprising that ecologists are not the most popular of people in a growth-oriented economy.