Fig. 5.

Conceptual model of the loss of resilience in aging societies. With time, resilient societies become fragile in the sense that even moderate perturbations may drive self-perpetuating change towards another state. Slopes of the valley represent rates of return upon perturbation of the states. Loss of resilience implies flatter slopes causing slower recovery from perturbations as confirmed for Neolithic (35) and for Pueblo societies (22) in the period leading up to collapse (adapted from ref. 22).