“The instructions to Adam and Eve about the garden earth . . .have not been rescinded. They were, and we are, to dress it—not destroy it. They were to take good care of it instead of abusing it. Our increasing interdependence on this planet makes some forms of individual selfishness the equivalent of a runaway personal bulldozer. If we have no concern for the generations to follow, the means are at hand to tear up the terrain much more than was ever possible anciently.”