Chapter 10 contends that the "wilderness" experienced by Europeans was an effect of the lapsed, large-scale environmental maintenance Indian societies had practiced. Borrowing from hypotheses from historians and anthropologists, Mann suggests that the pandemics that ravaged native civilizations in the 16th and 17th centuries led to a dramatic shift in the environment, creating the conditions European settlers were to experience in the New World. In this paradigm, as Europeans moved west, disease preceded them, sometimes by years. The effects of these pandemics weakened and suspended existing systems of environmental control, such as controlled burns, hunting, and terraces. This, in turn, created what Mann describes as "pathological" phenomena; that is, phenomena that occur through some breakdown of the system, rather than naturally. Two examples of these from Chapter 10 are the colossal herds of bison and flocks of passenger pigeons that dominated portions of the North American landscape. While these species were numerous prior to the establishment of Europeans on the continent, Mann hypothesizes that their numbers were controlled by hunting and farming. The decline and in some cases extinction of these species, Mann writes, were a result of the instability created by the sudden replacement of these large-scale environmental-management practices.