<P> 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 . </P> <P> 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 . </P> <P> The wave model has been proposed as an alternative to the tree model . The wave model groups languages, represented as isoglosses, and tracks the progress of language variation . The wave model does not rely on the nesting pattern inherent to the tree model . While the tree model implies a lack of contact between languages after derivation from an ancestral form, the wave model shows the relationship between languages that remain in contact, which is more realistic . </P> <P> 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 . </P>

Which of the following best defines the meaning of genetically related languages