Languages change over time. Eventually, they change so much that there is no similarity to the original. Estimates vary, but if a group of Americans were sent to a distant galaxy, after 10,000 years they would be speaking a language that would be no more similar to English than to Chinese, or Arabic.
Historical linguists like to construct family trees. A well-known one would be for the Romance languages: Latin separated into dialects, which evolved into different languages, including French, Spanish, Portuguese, Italian, and Rumanian.
Latin itself was a branch of Italic. Italic included other languages, long dead, such as Oscan.
Italic was a branch of Indo-European.
It appears to some linguists that all the languages of the world must have a common ancestor. Others disagree. It is difficult to reconcile a Proto-World language with what we know about prehistory. Pat Ryan and Joseph H. Greenberg have suggested that people coming out of northeast Africa around 50,000 BC spoke Proto-World. But that would violate the rule that no relationships would be recognizable after 10,000 years. If all the languages of the world are related, this relationship must have somehow formed more recently. Additionally, it contradicts genetic evidence that suggests the first humans migrated from the Horn of Africa into Yemen, rather than across the Sinai peninsula.
Dené-Caucasian has also been postulated to include Na-Dené (North America), Sino-Tibetan, Ket (Siberia), Burushashki (Pakistan), Caucasian (Chechen, Dagestan languages), and Basque. This language family is extremely hypothetical.
The Nostratic hypothesis was proposed by a Dane named Holger Pedersen, in 1903. The hypothesis claims that the Nostratic grouping includes such widely ranging language families as Indo-European, Afro-Asiatic, Uralic, Altaic, Sumerian, Elamo-Dravidian, and Kartvelian. Others claim other sets of languages. Some have speculated that the Nostratics were refugees from a Black Sea Flood of around 5600 BC, and some think this is the origin of the Noah's Flood Myth. However, the Nostratic family is widely considered disproven by linguists.
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