Large populations of asexual microbes evolve faster due to more mutations, but smaller populations can reach higher fitness levels. The shape of the environment's fitness landscape affects this trade-off. If there are many peaks, large populations get stuck on local peaks, while smaller populations can find higher peaks. The size of the target for mutations and the mutation rate also play a role in this trade-off. The best population size for adaptation depends on the environment and whether rapid evolution or high fitness is more important.