There have been several notable examples of scientists teaching signs to non-human primates in order to communicate with humans, such as chimpanzees, gorillas and orangutans. However, linguists generally point out that this does not constitute knowledge of a human language as a complete system, rather than simply signs/words. Notable examples of animals who have learned signs include: Chimpanzees: Washoe, Nim Chimpsky and Loulis Gorillas: Koko and Michael Gestural theory of human language origins One theory of the evolution of human language states that it developed first as a gestural system, which later shifted to speech. An important question for this gestural theory is what caused the shift to vocalization. See also Animal language Body language Braille Fingerspelling Chereme Chinese number gestures Hearing loss Gang signal Gestures Intercultural competence International Sign Legal recognition of sign languages List of international common standards List of sign languages List of sign languages by number of native signers Manual communication Metacommunicative competence Modern Sign Language communication Origin of language Origin of speech Sign language glove Sign language in infants and toddlers Sign language media Sign Language Studies (journal) Sign name Sociolinguistics of sign languages Tactile signing Machine translation of sign languages References Bibliography Branson, J., D. Miller, & I G. Marsaja. (1996). "Everyone here speaks sign language, too: a deaf village in Bali, Indonesia." In: C. Lucas (ed.): Multicultural aspects of sociolinguistics in deaf communities. Washington, Gallaudet University Press, pp. 39+ Deuchar, Margaret (1987). "Sign languages as creoles and Chomsky's notion of Universal Grammar." Essays in honor of Noam Chomsky, 81–91. New York: Falmer. Emmorey, Karen; & Lane, Harlan L. (Eds.). (2000). The signs of language revisited: An anthology to honor Ursula Bellugi and Edward Klima. Mahwah, NJ: Lawrence Erlbaum Associates. . Fischer, Susan D. (1974). "Sign language and linguistic universals." Actes du Colloque franco-allemand de grammaire générative, 2.187–204. Tübingen: Niemeyer. Goldin-Meadow, Susan (2003), The Resilience of Language: What Gesture Creation in Deaf Children Can Tell Us About How All Children Learn Language, Psychology Press, a subsidiary of Taylor & Francis, New York, 2003 Gordon, Raymond, ed. (2008). Ethnologue: Languages of the World, 15th edition. SIL International, . Sections for primary sign languages Browse by Language Family and alternative ones Browse by Language Family. Groce, Nora E. (1988). Everyone here spoke sign language: Hereditary deafness on Martha's Vineyard. Cambridge, Massachusetts: Harvard University Press. . Healy, Alice F. (1980). "Can Chimpanzees learn a phonemic language?" In: