# Evolution Strategy - ES

An ES works on a population of real valued solutions by repeated use of evolutionary operators like reproduction, recombination and mutation. λ offspring individuals are generated from μ parents by recombination and mutation (with μ < λ).
After evaluating the fitness of the λ offspring individuals, the comma-strategy selects the μ individuals with the best fitness as parent population for the next generation. On the other hand, a plus-strategy selects the best μ individuals from the aggregation of parents and offspring individuals, so in this case the best individual is guaranteed to survive. In general, however, the comma-strategy is more robust and can easier escape from local optima, which is why it is usually the standard selection.