The origin of speech refers to the general problem of the origin of language in the context of the physiological development of the human speech organs such as the tongue, lips, and vocal organs used to produce phonological units in all spoken languages. The origin of speech has been studied through many fields and topics such as: evolution, anatomy, and history of linguistics. The origin of speech is related to the more general problem of the origin of language, the evolution of distinctively human speech capacities has become a distinct and in many ways separate area of scientific research. The topic is a separate one because language is not necessarily spoken: it can equally be written or signed. Speech is in this sense optional, although it is the default modality for language.