Many of the characters Kolbert speaks to are conservationists whose zeal for the creatures in their care is inspiring, if a little quixotic. Take, for instance, the wardens of the Devils Hole pupfish, a tiny creature that lives in only one cave, in Death Valley, in a population that weighs less than a McDonald’s Filet-O-Fish. This cave is threatened by seeping toxic waste, so the US Fish and Wildlife Service has built the pupfish an almost exact replica. Swimming about in this “fishy Westworld”, the pupfish are now a “Stockholm species”, dependent on people for their survival.