Researchers report a sex difference in the expression of a language-associated protein in humans or animals. They analyzed the levels of Foxp2 protein in the brains of four-day-old female and male rats and compared the ultrasonic distress calls made by the animals when separated from their mothers and siblings. Compared with females, males had more of the protein in brain areas associated with cognition, emotion, and vocalization. They also made more noise than females—and were preferentially retrieved and returned to the nest first by the mother. Foxp2 protein levels were reduced in male pups and increased in female pups, they reversed the sex difference in the distress calls, causing males to sound like females and the females like males. This change led the mother to reverse her behavior as well, preferentially retrieving the females over the males. More tomorrow.