Environmental complexity favors the evolution of learning

Learning is a fundamental biological adaptation that is widespread throughout the animal kingdom. According to previous research, two conditions are necessary for learning to be adaptive: between-generation environmental variability and within-generation environmental predictability. In this paper, we show that between-generation variability is not necessary, and that instrumental learning can provide a selective advantage in complex environments, where an individual is exposed to a large number of different challenges during its lifespan. We construct an evolutionary model where individuals have a memory with limited storage capacity, and an evolving trait determines the fraction of that memory that should be allocated to innate responses to the environment versus learning these responses. The evolutionarily stable level of learning depends critically on the environmental process, but generally increases with environmental complexity. Overall, our work sheds light on the importance of global structural properties of the environment in shaping the evolution of learning.