Control of critical behavior in a small-scale social system
  Over the last decade new technologies for making large numbers of fine-grained measurements have led to the surprising discovery that many biological systems sit near a critical point. These systems are potentially more adaptive in that small changes to component behavior can induce large-scale changes in aggregate structure and function. Accounting for criticality remains a challenge as sensitivity to perturbation suggests a lack of robustness. Furthermore, change induced by perturbation may not be adaptive. Complicating matters further critical phenomena can result from history-dependent stochastic processes. A question central to distinguishing among these conflicting views of criticality is to what degree criticality can be controlled by the components of the system. We address the control of criticality using data on conflict dynamics and fight sizes from an animal society model system (Macaca nemestrina, n=48). The system is fundamentally finite so we operationalize criticality in information theoretic terms using Fisher information and a measure of instability. We analyze criticality using empirically-grounded equilibrium (maximum entropy) and dynamic (branching process) models of the monkeys' fight-joining behavior. We find that (1) this heterogeneous, socially organized system, like homogeneous, spatial systems (flocks and schools), sits near a critical point, (2) the contributions individuals make to how critical the system is can be quantified and vary, and (3) the distance from the critical point (DFC) can be controlled through biologically plausible mechanisms operating on this heterogeneity. These mechanisms include third-party policing, which dampens fight participation of the individuals with the largest effect on DFC. Control of DFC allows biological systems to balance the tradeoff between robustness and need for rapid change. 
Bryan C. Daniels, David C. Krakauer, and Jessica C. Flack
physics.soc-ph physics.bio-ph q-bio.PE