Complex adaptive systems, as conceived by John Holland, are groups of agents engaged in a process of coadaptation, in which adaptive moves by individuals have consequences for the group. Holland and others have shown that under certain circumstances simple models of this process show surprising abilities to self-organize (Holland 1993; Kauffman 1993). Complex adaptive systems have interesting mathematical properties, and the process of "anti-chaos"-—the spontaneous crystallization of ordered patterns in initially disordered networks— has become a new area of interdisciplinary research. But the question of whether these models can illuminate real world processes is still largely open. Not long ago John Maynard Smith described the study of complex adaptive systems as "fact-free science" (1995). This chapter has two purposes. First, in response to Maynard Smith, I will show how the concept of ecological feedback in complex adaptive systems provides a simple and powerful explanation for the structure and persistence of cooperative networks among Balinese rice farmers. Second, I will generalize this explanation to shed light on the emergence of cooperation in a class of social systems where interactions with the natural world create both rewards and punishments. But before turning to these examples, in line with the purposes of this volume I will comment on the ideas and assumptions that underlie the use of models in this analysis. "Society is a human product. Society is an objective reality. Man [sic] is a social product." With this epigram Peter Berger and Thomas Luckmann neatly encapsulated a fundamental problem in social theory (1967:61). In American anthropology today this paradox is often posed as a conflict between "structure" and "agency," where the former refers to ideational, economic, institutional, or psychological systems that are represented as generating social reality; and the latter to the ability of individual social actors to modify their own social worlds. The same paradox recurs in classical social theory, such as Jürgen Habermas' insistence on the need to somehow reconcile actor-focused and system-level social theories (Habermas 1985, 1987).
