Evolutionary Capacitance Emerges Spontaneously during Adaptation to Environmental Changes.

All biological populations are to a greater or lesser degree evolvable, but the forces that shape evolvability, especially the evolution of evolvability as an adaptive response to pressure to evolve rapidly, are a source of controversy. One determinant of evolvability is the set of possible mutations available to a genotype, or "mutational neighborhood." A benign (instead of deleterious) mutational neighborhood can enhance evolvability. Whether selection for evolvability itself can result in a more benign mutational neighborhood remains an open question. We document the evolution of increased evolvability in a fluctuating environment despite using a regime that precludes, by design, the adaptive evolution of evolvability. Instead, a benign mutational neighborhood arises as a byproduct of transiently elevated error rates via a mechanism that we call emergent evolutionary capacitance. This is evolutionary capacitance similar to that seen in a model system for capacitance, the yeast prion [PSI+], but without a capacitor.