Evolution can get stuck. When no mutations are available that can improve the fitness of an organism, evolution cannot proceed. However, using environmental fluctuations that are ubiquitous in nature, evolution can proceed. In the preprint that we posted earlier on the bioRxiv and which has recently been published in PNAS we describe how a transcription factor and its binding site, constraint in the different constant environments, can evolve in fluctuating environments.

Stalled evolution

Concept of fitness landscape. From de Visser & Krug,Nature Reviews Genetics 15, 480–490 (2014)

The accessibility of phenotypes in different environments depends on the wiring of the genotype-phenotype map and the translation of this map into fitness. When sub-optimal genotypes are surrounded by valleys in the adaptive landscape, neighboring genotypes are inaccessible and evolution is unable to proceed by single mutational step-by-step positive Darwinian evolution (Figure 1).