Sex differences in language first appear in gesture.

Children differ in how quickly they reach linguistic milestones. Boys typically produce their first multi-word sentences later than girls do. We ask here whether there are sex differences in children's gestures that precede, and presage, these sex differences in speech. To explore this question, we observed 22 girls and 18 boys every 4 months as they progressed from one-word speech to multi-word speech. We found that boys not only produced speech + speech (S+S) combinations ('drink juice') 3 months later than girls, but they also produced gesture + speech (G+S) combinations expressing the same types of semantic relations ('eat' + point at cookie) 3 months later than girls. Because G+S combinations are produced earlier than S+S combinations, children's gestures provide the first sign that boys are likely to lag behind girls in the onset of sentence constructions.