A number of [[sign language]]s have arisen independently, without any ancestral language, and thus are language isolates. TheThese most famous of these is theinclude [[Nicaraguan Sign Language]], a well-documented case of what has happened in schools for the deaf in many countries.<ref name="journals.sagepub.com"/> In Tanzania, for example, there are seven schools for the deaf, each with its own [[Tanzanian sign languages|sign language]] with no known connection to any other language.<ref>{{Cite book|last=T.|first=Muzale, H. R.|title=Kamusi ya Lugha ya Alama ya Tanzania (LAT) = Tanzanian Sign Language (TSL) dictionary: Kiswahili-TSL-English|date=2004|publisher=Languages of Tanzania Project, University of Dar es Salaam|isbn=9987-691-02-1|oclc=67947374}}</ref> Sign languages have also developed outside schools, in communities with high incidences of deafness, such as [[Kata Kolok]] in Bali, and half a dozen sign languages of the hill tribes in Thailand including the [[Ban Khor Sign Language]].<ref name=":3">{{Cite journal|last=de Vos|first=Connie|date=March 2011|title=Kata Kolok Color Terms and the Emergence of Lexical Signs in Rural Signing Communities|url=http://www.tandfonline.com/doi/full/10.2752/174589311X12893982233795|journal=The Senses and Society|language=en|volume=6|issue=1|pages=68–76|doi=10.2752/174589311X12893982233795|hdl=11858/00-001M-0000-0012-BB5A-6|s2cid=218839277 |issn=1745-8927|hdl-access=free}}</ref><ref>{{Cite journal|last=Nonaka|first=Angela M.|date=July 2009|title=Estimating size, scope, and membership of the speech/sign communities of undocumented indigenous/village sign languages: The Ban Khor case study|url=https://linkinghub.elsevier.com/retrieve/pii/S0271530909000202|journal=Language & Communication|language=en|volume=29|issue=3|pages=210–229|doi=10.1016/j.langcom.2009.02.004}}</ref>
These and more are all presumed isolates or small local families, because many deaf communities are made up of people whose hearing parents do not use sign language, and have manifestly, as shown by the language itself, not borrowed their sign language from other deaf communities during the recorded history of these languages.<ref name=":3" />
