Book excerpt: In Defense of the Land Ethic: Essays in Environmental Philosophy brings into a single volume J. Baird Callicott’s decade-long effort to articulate, defend, and extend the seminal environmental philosophy of Aldo Leopold. A leading voice in this new field, Callicott sounds the depths of the proverbial iceberg, the tip of which is “The Land Ethic.” “The Land Ethic,” Callicott argues, is traceable to the moral psychology of David Hume and Charles Darwin’s classical account of the origin and evolution of Hume’s moral sentiments. Leopold adds an ecological vision of organic nature to these foundations. How can an evolutionary and ecological environmental ethic bridge the gap between is and ought? How may wholes—species, ecosystems, and the biosphere itself—be the direct objects of moral concern? How may the intrinsic value of nonhuman natural entities and nature as a whole be justified? In addition to confronting and resolving these distinctly philosophical queries, Callicott engages in lively debate with proponents of animal liberation and rights—finally to achieve an integrated theory of animal welfare and environmental ethics. He critically discusses the land ethic that is alleged to have prevailed among traditional American Indian peoples and points toward a new and equally revolutionary environmental aesthetic.