Memory (i.e. the ability to store and retrieve information) plays a crucial role in the development of an animal’s behavior within its lifespan and is often important for its survival and reproductive success. Memory is itself a product of evolution and the degree to which information is maintained in the brain varies among species and among different types of behavior. Findings from vertebrate behavioral pharmacology have challenged the traditional view of memory formation as a direct flow from short-term to long-term storage. Evidence points instead to an intricate, multiphase pathway of memory consolidation. Different components of memory emerge at different times after the event to be memorized takes place. In addition, their duration and times of onset can vary with different tasks and species If variations in memory capacities have been observed among closely-related species, the relationship between environmental conditions and evolution of these capacities have only been rarely studied despite the importance of this topic in the understanding of the evolution of behavior. I propose an experimental approach using Drosophila as a model system. This project concentrates on: Part 1: Genetic variation of the memory phases Part 2: Effect of the environmental conditions on the development of memory Part 3: fitness cost of memory Part 4: Consolidation, Reconsolidation and Extinction: similar or separate processes?