Which process involves the gradual change of a species over time to better fit their environment?

The process that involves the gradual change of a species over time to better fit their environment is evolution. Evolution is driven by mechanisms such as natural selection, where individuals with traits that confer a survival or reproductive advantage are more likely to pass on their genes to the next generation. Over long periods, this can lead to significant changes in a species, making them more suited to their environment.

While adaptation refers to specific traits or features that enhance the survival and reproductive success of organisms within a particular environment, it is part of the broader process of evolution. Migration, on the other hand, involves the movement of individuals from one location to another and does not inherently cause changes in species. Extinction is the termination of a species and does not involve changes that lead to better adaptation or fit within an environment. Therefore, evolution is the most comprehensive term that encompasses the gradual changes in species over time.