Interactions between mutations can make predicting evolution tricky, but a recent study found that the effect of a mutation can often be predicted from its genetic background. This can help us understand how organisms adapt to different environments, like when developing drug resistance. By studying mutations in a malaria parasite gene, researchers discovered that the way mutations interact with each other can change depending on the drug concentration in the environment. This shows that environmental factors can significantly impact how mutations affect an organism's fitness, which is important for predicting how organisms will adapt in changing environments.