It was observed in evolution strategies that significant progress toward the fitness/objective function's optimum, generally, can only happen in a narrow band of the mutation step size σ. That narrow band is called evolution window.

There are three well-known methods to adapt the mutation step size σ in evolution strategies:

• (1/5-th) Success Rule
• Self-Adaptation (for example through log-normal mutations)
• Cumulative Step Size Adaptation (CSA)

On simple functions all of them have been empirically shown to keep the step size within the evolution window.