Looking For Relationships
It is possible that all oral languages spoken in the world today are related by direct or indirect descent from a single ancestral tongue. The established language families would then be only the upper branches of the genealogical tree of all (or most) languages, or, equally, lower progeny of a parent tongue. For this reason, language isolates have been the object of numerous studies seeking to uncover their genealogy. For instance, Basque has been compared with every living and extinct Eurasian language family known, from Sumerian to South Caucasian, without conclusive results.
There are some situations in which a language with no ancestor might arise. This frequently happens with sign languages, most famously in the case of Nicaraguan Sign Language, where deaf children with no language were placed together and developed a new language. Similarly, if deaf parents were to raise a group of hearing children who have no contact with others until adulthood, they might develop an oral language among themselves and keep using it later, teaching it to their children, and so on. Eventually, it could develop into the full-fledged language of a population. With oral languages, this is not very likely to occur at any one time but, over the tens of thousands of years of human pre-history, the likelihood of this occurring at least a few times increases. There are also creole languages and constructed languages such as Esperanto which do not descend directly from a single ancestor but have become the language of a population; however, they do take elements from existing languages.
Read more about this topic: Language Isolate