“Why do we care about diversity?” Assuming that biological and, to a lesser extent, cultural diversity are accepted as important values in current Western society, how did this come to pass, and have we always thought this way? That is the central question addressed in this book.While many existing books on biodiversity have examined various dimensions of the current crisis, mine takes a different approach. Catastrophic Thinking reconstructs the historical process by which diversity came, over the past two centuries, to be held as an intrinsic value. Ultimately, I argue that the celebration of diversity—in both biological and cultural forms—is a fairly recent invention. And the key concept running throughout this story is extinction.We care about biodiversity in large part because we fear the consequences of its loss: the loss of plants that might provide the basis for new medicines, the depletion of environments that provide so-called “ecosystem services” on which our own species depends, the disappearance of animals we value for food and recreation. In other words, the single, unified threat to biological diversity is extinction—or more precisely, mass extinction, which involves the coordinated and cascading extinctions of many groups of organisms in a relatively short period of time.Surprisingly, however, extinction was not a major area of scientific study prior to about 50 years ago, nor did Western culture attach much significance to the general phenomenon. Indeed, during much of the nineteenth century and well into the twentieth, Western scientists regarded extinction as a slow, piecemeal process that punished nature’s “losers” and rewarded those species that are better adapted for their environments. Charles Darwin, for example, rejected the notion that mass extinctions had ever occurred in the geologic past, and it wasn’t until the 1970s that scientists began to take extinction seriously. Because extinction was not seen as a threat to the health of the environment, the preservation of biological diversity—and, by extension, cultural diversity—was simply not considered an important value in Darwin’s day.Clearly, we see things very differently today, but this enormous shift in values has not been documented in a comprehensive way. Catastrophic Thinking tells the story of how a major scientific and cultural shift in thinking about the consequences of extinction—and ultimately, diversity—took place over the last 200 years, from a culture that valued diversity very little to one in which it is held up as a central value. One of the key points of transformation occurred during the 1970s and 1980s, when the reality of past global, catastrophic mass extinctions was accepted. This scientific shift was conditioned by a broader set of political and cultural debates and events spanning the twentieth century: two world wars, nuclear proliferation, political upheaval, and environmental disasters all contributed to the sense that human history had entered an age of crisis. Scientific consensus about catastrophic change, in other words, was influenced by and has reinforced a broader “catastrophic thinking” about the fate of human civilization. It is in this context, I argue, that we have come to value diversity, because only at this later date have Westerners tied the fate of our own species to that of the broader natural environment we inhabit. Our current moment, in which the threat of anthropogenic climate change and species loss challenges us to consider whether we have permanently altered the geological and evolutionary trajectory of our planet, is both a consequence of this longer history, and an opportunity to conceive of new ways of thinking about our future.