  Successful adaptation helped the emergence of complexity. Alternating
plastic- and rigid-like states were recurrently considered to play a role in
adaptive processes. However, this extensive knowledge remained fragmented. In
this paper I describe plasticity-rigidity cycles as a general adaptation
mechanism operating in molecular assemblies, assisted protein folding, cellular
differentiation, learning, memory formation, creative thinking, as well as the
organization of social groups and ecosystems. Plasticity-rigidity cycles enable
a novel understanding of aging, exploration/exploitation trade-off and
evolvability, as well as help the design of efficient interventions in medicine
and in crisis management of financial and biological ecosystems.
