An Evolutionary Stable Strategy (ESS) is a concept from evolutionary game theory that describes a strategy which, if adopted by a population, cannot be invaded by any alternative strategy. This means that if most individuals in a population use this strategy, any mutant strategy that arises will not be able to outperform it, ensuring the stability of the original strategy over time. The idea of ESS was introduced by the biologist John Maynard Smith in the context of animal behavior and evolutionary biology. It helps explain how certain traits or behaviors can persist in a population, as they provide a competitive advantage in survival and reproduction, thus shaping the evolution of species.