A language isolate is a natural language with no demonstrable genetic relationship with other living languages; that is, one that has not been proved to descend from a common ancestor to any other language. Commonly cited examples include Korean, Basque, Ainu, Burushaski, and Japanese, although in each case a minority of linguists claims to have demonstrated a relationship with another language (see Dene-Caucasian and Altaic).
Some languages became isolates in historical times, after all their known relatives became extinct. The Pirahã language of Brazil is one such example, the last surviving member of the Mura family. Others, like Basque, have been isolates for as long as their existence has been documented.
Language isolates may be seen as a special case of unclassified languages, being languages which remain unclassified even after extensive efforts. If eventually such efforts do prove fruitful, a language previously considered an isolate may no longer be considered one; and since linguists do not always agree on whether a genetic relationship has been demonstrated, it is often disputed whether a language constitutes a true isolate or not.
A second use of the term understands "isolate" to be within a particular context. For instance, Albanian and Armenian are considered isolates within Indo-European. While part of the Indo-European family, they have no demonstrable close genetic relationship with any particular languages, but instead form independent branches of their own. However, without a disambiguating context, "isolate" is understood to be in the absolute sense.
The term "genetic relationship" is meant in the sense of historical linguistics, which claims that almost all languages spoken in the world today can be grouped by derivation from common ancestral languages into a relatively small number of families. For example, English is related to other Indo-European languages and Mandarin is related to many other Sino-Tibetan languages. By this criterion, each language isolate constitutes a family on its own, which explains the exceptional interest that those languages have received from linguists.
Looking for relationship
It is possible, though not certain, that all languages spoken in the world today are genetically related by descent from a single ancestral tongue. The established language families would then be only the upper branches of the genealogical tree of all languages. For this reason, isolate languages have been the object of numerous studies seeking to uncover their genealogy. For instance, Basque has been compared with every living and extinct language family known, from Sumerian to the South Caucasian — without conclusive results.
There are some situations in which a language with no ancestor might arise. For example, if deaf parents were to raise a group of hearing children who have no contact with others until adulthood, they might develop a verbal 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. Such a situation is not very likely to occur at any one time but, looking at tens of thousands of years of human history plus pre-history, the likelihood of this occurring at least a few times increases.
Isolate, not isolated
One should not confuse the concept of a language isolate with a language whose speakers are isolated in some sense, such as people who have little contact with other cultures (like the Rapa Nui language of Easter Island) or because they live far away from the regions where related languages are spoken (like the Malagasy language of Madagascar whose closest relatives are spoken in Kalimantan). These two languages are definitely not isolates.
List of language isolates
Below is a list of known language isolates, along with notes on possible relations to other languages or language families:
No known living relatives; found in the Basque region of France and Spain. Aquitanian is commonly regarded as a direct ancestor of Basque. Some linguists have claimed similarities with various languages of the Caucasus, especially because of its ergative case system, but the resemblances seem superficial. Other linguists have proposed a relation to Iberic.
Related to languages that have recently become extinct. Only known language with no number terminology, grammatical recursion, and several other unique features.
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