...chimpanzees and bonobos also make liberal use of gestures in addition to the sounds and facial expressions that are part of their communication system...
D. Díaz, R. Ramírez, and D. Hernández-Leo. IEEE 15th International Conference on Advanced Learning Technologies (ICALT); 2015 Jul 06-Jul 09; Hualien, Taiwan.Sl: IEEE, 2015. p. 367-369., Institute of Electrical and Electronics Engineers (IEEE), (2015)