Kauê M. Costa was a Ph.D. student in Germany trying to understand how amphetamines cause hyperactivity when he noticed his mice were acting weird. The mice were genetically engineered to help researchers study dopamine in the brain, and they were unusually hyperactive. The amphetamines they were taking calmed the females but not the males. The mice were learning differently based on sex, and this divergence was scrambling his results. Born in Amazonian Brazil, Costa is now an assistant...