In linguistics, genetic relationship is the usual term for the relationship which exists between languages that are members of the same language family. The term genealogical relationship is sometimes used to avoid confusion with the unrelated use of the term in biological genetics. Languages that possess genetic ties with one another belong to the same linguistic grouping, known as a language family. These ties are established through use of the comparative method of linguistic analysis.
Two languages are considered to be genetically related if one is descended from the other or if both are descended from a common ancestor. For example, Italian is descended from Latin. Italian and Latin are therefore said to be genetically related. Spanish is also descended from Latin. Therefore, Spanish and Italian are genetically related. In a similar way, Danish, Swedish and Norwegian are genetically related through the North Germanic branch of the Indo-European language family.
The classification of languages into language families begins by making a list of words in the potential languages that exhibit lexical and grammatical similarities; that is, they are similar in sound and meaning. The next step is to determine how the similarities originated. There are three possibilities: convergence, borrowing and common origin. Convergence is the chance similarity of sound and meaning of a word in two different languages and "is based on the principle that a word is an arbitrary association of sound and meaning". An example of convergence is that many unrelated languages have words similar to mama and papa for 'mother' and 'father'. Borrowing results from the exchanging of words between languages in close contact with one another. Once convergence and borrowing have been eliminated as possible explanations for similarities in sound and meaning of words, the last explanation is common origin. It can be assumed that the similarities occurred due to descent from a common ancestor, and the words are known as cognates. The set of all cognates of a word is the etymology of the word.
Linguistic interference and borrowing
When languages are in contact with one another, either of them may influence the other through linguistic interference such as borrowing. For example, French has influenced English, Arabic has influenced Persian, and Chinese has influenced Japanese in this way. However, such influence does not constitute (and is not a measure of) a genetic relationship between the languages concerned. Linguistic interference can occur between languages that are genetically closely related, between languages that are distantly related (like English and French, which are distantly related Indo-European languages) and between languages that have no genetic relationship.
One theory concerning genetic relationships among languages is monogenesis – the idea that all known languages, with the exceptions of creoles, pidgins and sign languages, are descendant from a single ancestral language.
A common visual representation of a language family is given by a genetic language tree. The tree model is sometimes termed a dendrogram or phylogeny. The family tree shows the relationship of the languages within in a family, much as a family tree of an individual shows their relationship with their relatives. There are criticisms to the family tree model. Critics focus mainly on the claim that the internal structure of the trees is subject to variation based on the criteria of classification. Even among those who support the family tree model, there are debates over which languages should be included in a language family. For example, within the dubious Altaic language family, there are debates over whether the Japonic and Koreanic languages should be included or not.
The wave model has been proposed as an alternative to the tree model. The wave model uses isoglosses to group language varieties; unlike in the tree model, these groups can overlap. While the tree model implies a lack of contact between languages after derivation from an ancestral form, the wave model emphasizes the relationship between languages that remain in contact, which is more realistic.
Some problems encountered by the genetic relationship group of languages include language isolates and mixed, pidgin and creole languages. Mixed languages, pidgins and creole languages constitute special genetic types of languages. They do not descend linearly or directly from a single language and have no single ancestor. Language isolates are languages that are unrelated to other languages. Each language isolate is considered to be a single language family with one language according to the Ethnologue. Including language isolates when counting language families considerably increases the number of language families.
- Lewis, M. Paul, Gary F. Simons, and Charles D. Fennig (eds.). Ethnologue: Languages of the World, Seventeenth edition. Dallas, Texas: SIL International, 2013.
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- Nichols, Johanna. Monogenesis or Polygenesis: A Single Ancestral Language for All Humanity? Ch. 58 of The Oxford Handbook of Language Evolution, ed. by Maggie Tallerman and Kathleen Rita Gibson. Oxford: Oxford UP, 2012. 558-72. Print.
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- Georg, Stefan, Peter A. Michalove, Alexis Manaster Ramer, and Paul J. Sidwell. Telling General Linguists about Altaic. Journal of Linguistics 35.1 (1999): 65-98. Print.
- Francois, Alexandre. Trees, Waves and Linkages: Models of Language Diversification. In The Routledge Handbook of Historical Linguistics, ed. by Claire Bowern and Bethwyn Evans. New York: Routledge, 2014, pp.161-189. (ISBN 978-0-41552-789-7).