Fluctuations and correlations in physical and biological nanosystems: the tale is in the tails

The inherently small system sizes involved imply that, in the absence of large applied fields designed to overwhelm them, fluctuations will play a major role in determining the response and functionality of nanoscale systems. Theoretical advances over the past two decades have provided fresh insight into fluctuations and their role at the nanoscale, even in the presence of arbitrarily large applied external fields. In contrast to traditional engineered systems, Nature's approach to nanotechnology is to embrace and to exploit fluctuations and noise to create adaptable, persistent, optimized functional architectures. We describe some of the mechanisms by which Nature exploits noise, with the goal of applying these lessons to engineered physical and chemical nanosystems. In particular, we emphasize the critical role of the tails of distributions of properties in both physical and biological nanosystems and their impact on system behavior.