The study looked at how fruit fly populations changed over time in different environments. After five generations, populations that were not well-suited to their environment died out, while those on cherry, strawberry, and cranberry survived. Fitness improved in all environments after five generations, and this trend continued after 26 generations, except for cranberry populations on cherry. This suggests that cherry and cranberry environments have very different optimal fitness levels. Studying fitness changes over time and in different environments helps us understand how fruit flies adapt to their surroundings.