There are still a few places in the world where one can sense what Earth was like before the advent of human beings. In the aisles of a tropical rainforest such as the one that fl ourishes by the Río Napo in Peru, there are so many species of trees that often one has to walk some distance before fi nding the same one twice, and the variety of iridescent butterfl ies, mantises, and other insects is incredible. In a cave under the coastal cliffs of Oregon, open to the breakers of the seemingly changeless ocean, the great sea lions bark clouds of steam above pools where mussels and anemones cling amid a constantly moving throng of crustaceans. At evening in springtime around a desert water hole in Organ Pipe Cactus National Monument, Arizona, bright fl owers spice the air as bighorn sheep lower their heads and bats dive to the surface, drinking on the wing. Earth before humankind appeared was a place of abundant biodiversity and of dynamic balance among species and elements.