section_path: Evolution
section_name: Evolution
paragraph_text: Evolution
  
  Although 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.
  
  Monkeys, non-human apes and humans, like many other animals, have evolved specialised mechanisms for producing sound for purposes of social communication. On the other hand, no monkey or ape uses its tongue for such purposes. The human species' unprecedented use of the tongue, lips and other moveable parts seems to place speech in a quite separate category, making its evolutionary emergence an intriguing theoretical challenge in the eyes of many scholars.
  
  Determining the timeline of human speech evolution is made additionally challenging by the lack of data in the fossil record. The human vocal tract does not fossilize, and indirect evidence of vocal tract changes in hominid fossils has proven inconclusive.