A rat study has found that infant males have more of the Foxp2 protein (associated with language development) than females and that males also made significantly more distress calls than females. Increasing the protein level in females and reducing it in males reversed the gender differences in alarm calls.
A small pilot study with humans found that 4-year-old girls had more of the protein than boys. In both cases, it is the more communicative gender that has the higher level of Foxp2.
 . Foxp2 Mediates Sex Differences in Ultrasonic Vocalization by Rat Pups and Directs Order of Maternal Retrieval. The Journal of Neuroscience [Internet]. 2013 ;33(8):3276 - 3283. Available from: http://www.jneurosci.org/content/33/8/3276