Leopold begins Part 4 with an argument for extending ethics—which over millennia have come to include more categories of people, by defining social behavior and constraining individual freedoms for the good of the whole—to land, thereby extending the human community “to include soils, waters, plants, and animals” (239). This idea is different from love for the land, he writes, which many people already express, and which has not prevented the despoliation of rivers, erosion of soils, and extinction of species. A land ethic, by contrast, asserts respect for the rights of ecosystems (and their constituent parts) to exist. This position is not only morally right, Leopold thinks, but also expedient, as the existing attitude of humans to nature—that of conqueror—presupposes a depth of understanding of nature that humans do not possess. Instead, humans should see themselves as part of a biological community that contains forces beyond their comprehension.

The other problem with the conservation system is that it is based on economic motives, Leopold writes: “One basic weakness in a conservation system based wholly on economic motives is that most members of the land community have no economic value” (246). To save species, conservationists often try to justify their existence in economic terms, but such justifications are weak.