Genetic relationship (linguistics) in the context of "Language isolates"

A language isolate, or an isolated language, is a language that has no demonstrable genetic relationship with any other languages. Basque in Europe, Ainu and Burushaski in Asia, Sandawe in Africa, Haida and Zuni in North America, Kanoê and Trumai in South America, and Tiwi in Oceania are all examples of such languages. The exact number of language isolates is yet unknown due to insufficient data on several languages.

One explanation for the existence of language isolates is that they might be the last remaining member of a larger language family. Such languages might have had relatives in the past that have since disappeared without being documented, leaving them an orphaned language. One example is the Ket language spoken in central Siberia, which belongs to the wider Yeniseian language family; had it been discovered in recent times independently from its now extinct relatives, such as Yugh and Kott, it would have been classified as an isolate. Another explanation for language isolates is that they arose independently in isolation and thus do not share a common linguistic genesis with any other language but themselves. This explanation mostly applies to sign languages that have developed independently of other spoken or signed languages.

In linguistics, the comparative method is a technique for studying the development of languages by performing a feature-by-feature comparison of two or more languages with common descent from a shared ancestor and then extrapolating backwards to infer the properties of that ancestor. The comparative method may be contrasted with the method of internal reconstruction in which the internal development of a single language is inferred by the analysis of features within that language. Ordinarily, both methods are used together to reconstruct prehistoric phases of languages; to fill in gaps in the historical record of a language; to discover the development of phonological, morphological and other linguistic systems and to confirm or to refute hypothesised relationships between languages.

The comparative method emerged in the early 19th century with the birth of Indo-European studies, then took a definite scientific approach with the works of the Neogrammarians in the late 19th–early 20th century. Key contributions were made by the Danish scholars Rasmus Rask (1787–1832) and Karl Verner (1846–1896), and the German scholar Jacob Grimm (1785–1863). The first linguist to offer reconstructed forms from a proto-language was August Schleicher (1821–1868) in his Compendium der vergleichenden Grammatik der indogermanischen Sprachen, originally published in 1861. Here is Schleicher's explanation of why he offered reconstructed forms:

In historical linguistics, the tree model (also Stammbaum, genetic, or cladistic model) is a model of the evolution of languages analogous to the concept of a family tree, particularly a phylogenetic tree in the biological evolution of species. As with species, each language is assumed to have evolved from a single parent or "mother" language, with languages that share a common ancestor belonging to the same language family.

Popularized by the German linguist August Schleicher in 1853, the tree model has been a common method of describing genetic relationships between languages since the first attempts to do so. It is central to the field of comparative linguistics, which involves using evidence from known languages and observed rules of language feature evolution to identify and describe the hypothetical proto-languages ancestral to each language family, such as Proto-Indo-European and the Indo-European languages. However, this is largely a theoretical, qualitative pursuit, and linguists have always emphasized the inherent limitations of the tree model due to the large role played by horizontal transmission in language evolution, ranging from loanwords to creole languages that have multiple mother languages. The wave model was developed in 1872 by Schleicher's student Johannes Schmidt as an alternative to the tree model that incorporates horizontal transmission.

The Indigenous languages of the Americas are the languages that were used by the Indigenous peoples of the Americas before the arrival of Europeans. Over a thousand of these languages are still used today, while many more are now extinct. The Indigenous languages of the Americas are not all related to each other; instead, they are classified into a hundred or so language families and isolates, as well as several extinct languages that are unclassified due to the lack of information on them.

Many proposals have been made to relate some or all of these languages to each other, with varying degrees of success. The most widely reported is Joseph Greenberg's Amerind hypothesis, which, however, nearly all specialists reject because of severe methodological flaws; spurious data; and a failure to distinguish cognation, contact, and coincidence.

Comparative linguistics is a branch of historical linguistics that is concerned with comparing languages to establish their historical relatedness.

Genetic relatedness implies a common origin or proto-language and comparative linguistics aims to construct language families, to reconstruct proto-languages and specify the changes that have resulted in the documented languages. To maintain a clear distinction between attested and reconstructed forms, comparative linguists prefix an asterisk to any form that is not found in surviving texts. A number of methods for carrying out language classification have been developed, ranging from simple inspection to computerised hypothesis testing. Such methods have gone through a long process of development.

The classification of the Japonic languages and their external relations is unclear. Linguists traditionally consider the Japonic languages to belong to an independent family; indeed, until the classification of Ryukyuan and eventually Hachijō as separate languages within a Japonic family rather than as dialects of Japanese, Japanese was considered a language isolate.

Among more distant connections, the possibility of a genetic relationship to languages like Austronesian and or Kra–Dai, are discussed. A relation between Japonic and Koreanic is also considered plausible by some linguists, while others reject this idea. Independent of the question of a Japonic–Koreanic connection, both the Japonic and Koreanic languages are sometimes included in the now largely discredited Altaic family.

In historical linguistics, the homeland or Urheimat (/ˈʊərhaɪmɑːt/ OOR-hye-maht, from German ur- 'original' and Heimat 'home') of a proto-language is the region in which it was spoken before splitting into different daughter languages. A proto-language is the reconstructed or historically attested parent language of a group of languages that are genetically related.

Depending on the age of the language family under consideration, its homeland may be known with near-certainty (in the case of historical or near-historical migrations) or it may be very uncertain (in the case of deep prehistory). Next to internal linguistic evidence, the reconstruction of a prehistoric homeland makes use of a variety of disciplines, including archaeology and archaeogenetics.

Dene–Yeniseian (/dɪˈneɪ ˌjɛnɪˈseɪ.ən/, dih-NAY YEN-ih-SAY-ən) is a proposed language family consisting of the Yeniseian languages of central Siberia and the Na-Dene languages of northwestern North America.

Reception among experts has been somewhat favorable; thus, Dene–Yeniseian has been called "the first demonstration of a genealogical link between Old World and New World language families that meets the standards of traditional comparative-historical linguistics". Other linguistic scholars have deemed Dene–Yeniseian only as "plausible".

The Khoisan languages (/ˈkɔɪsɑːn/ KOY-sahn; also Khoesan or Khoesaan) are a number of African languages once classified together, originally by Joseph Greenberg. Khoisan is defined as those languages that have click consonants and do not belong to other African language families. For much of the 20th century, they were thought to be genealogically related to each other, but this is no longer accepted. They are now held to comprise three distinct language families and two language isolates.

All but two Khoisan languages are indigenous to southern Africa; these are classified into three language families. The Khoe family appears to have migrated to southern Africa not long before the Bantu expansion. Ethnically, their speakers are the Khoekhoe and the San (Bushmen). Two languages of eastern Africa, those of the Sandawe and Hadza, were originally also classified as Khoisan, although their speakers are ethnically neither Khoekhoe nor San.