 In contrast to Rawls' basic optimism, environmentalists have recently produced some of the most alarming criticisms of the idea of progress. Jared Diamond and Ronald Wright are examples.  The authors share three basic theoretical commitments.  First, they point to the natural environment as the most important determinant of long-term social stability and change.  Next, they appeal to historical examples to argue that change is non-linear and that environmental variables explain the non-linearity.  Then, extrapolating from past collapses, they argue that recent growth rates should not encourage optimism. Instead, global collapse is a real possibility. 