Spoken language is a form of communication in which people uses the mouth to create recognizable sounds. These sounds come from a large vocabulary of sequences of sounds with agreed-upon meanings. These sequences of sounds are called words, and each represents one or more objects or concepts. A shared grammar and syntax allow the speaker to form these words into statements which listeners will be able to understand.
The origins of spoken language remain unclear, although they are the subject of ongoing research by anthropologists. Skeletal evidence suggests that early hominids used some form of vocal communication, but it is not certain when this first became complex enough to be considered spoken language. Vocal communication occurs in many species of animals, from birds to cetaceans, but this communication does not appear to possess the grammar and vocabulary which would qualify it as a language. A 2006 study in the Journal of the Acoustical Society of America suggests that the anatomy for speech developed in humans approximately 100,000 years ago. The development of written language is extremely difficult to trace in either the archaeological or fossil record because, unlike written language, it leaves no physical trace.
Spoken language is not the only form of human communication. Written language conveys meaning through the use of writing, in which visual symbols correspond to the meanings and sounds of words. Many languages have both a written and a spoken form, although there are a number of languages which have a spoken form but no written form. For example, the Mosuo, an ethnic group who live near Lugu Lake in China's Yunnan Plateau, have an indigenous language which is only spoken. The reverse is much rarer, although some ancient languages, like Latin, have spoken forms which are basically extinct while their written forms have survived in the archaeological record.
While spoken language uses sound to convey meaning and written language uses images, sign language uses the movement of the body to communicate. Modern sign languages developed from systems intended to communicate between people who could not use spoken language, either because their hearing or speech were impaired or because cultural factors prevented them from speaking. This was the case among medieval monks, who used signs to communicate during periods when they were not permitted to speak. One theory of the origin of language, the gestural theory, suggests that languages based on gestures actually predate the origin of spoken language.