Researchers studied the levels of Foxp2 protein in the brains of four-day-old female and male rats first. Then they turned their attention to human children. In a preliminary study of Foxp2 protein in a small group of children, researchers found that girls had more of the Foxp2 protein in the cortex, a brain region associated with language, than age-matched boys. This was opposite from what they found in male and female rat brains.
J. Michael Bowers. et al. “Foxp2 Mediates Sex Differences in Ultrasonic Vocalization by Rat Pups and Directs Order of Maternal Retrieval.” The Journal of Neuroscience, February 20, 2013; Vol. 33, Issue 8:pages 3276 %u20133283 DOI: 10.1523/JNEUROSCI.0425-12.2013