“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 have not been rescinded.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.”