Over a century ago linguists established that the Armenian language is a separate branch of the Indo-European language family.11 Armenian, English, French, Russian, Greek, Albanian, Hindi, Farsi, and a hundred or more other languages exhibit striking correspondences in their sound systems, vocabulary and grammar. Statistically, those correspondences could not be random; they could have resulted only if these languages came from a common source.12 Linguists have adopted the metaphor of a language family for languages so related, calling that common, reconstructed source from which these languages descended, Proto-Indo-European.13
That languages develop this way is evident from the historical record of such languages as French, Spanish, Italian, Romanian, and Portuguese. These are relatively new offshoots of the Romance branch of the Indo-European family. Their similarities in vocabulary, sounds, and grammar show that they derived from dialects of Latin during the centuries after the break-up of the Roman Empire (AD 500-1000).
11H.Hübschmann, “On the Position of Armenian in the Sphere of the Indo-European Languages,”  165-189 in W.F. Lehmann, ed. & trans., A Reader in 19th Century Historical Indo-European Linguistics (Bloomington: Indiana U. Press, 1967); see also, A. Meillet, Esquisse d’une grammaire comparée de l’arménien classique (Vienna: Mekhitarist Press, 1936); Robert Godel, An Introduction to the Study of Classical Armenian (Wiesbaden: Dr. Ludwig Reichert Verlag, 1975); Sarkis Saryan, Language Connections: Kinship of Armenian with Sister Indo-European Languages (Yarmouth, MA: Sarmen, 1982).
12See, e.g., Isidore Dyen, Joseph B. Kruskal & Paul Black, An Indoeuropean Classification: A Lexicostatistical Experiment, Transactions of the American Philosophical Society, vol. 82, pt. 5 (Philadelphia: The American Philosophical Society, 1992); E. D. Polivanov, “Even Mathematics can be Useful,” 226-272, in Selected Works, ed. Leont’ev, ed., D. Armstrong, trans. (The Hague: Mouton, 1974).
13See, Colin Renfrew, Language and Archaeology, 98-119; Winfred P. Lehmann, ed. & trans., A Reader in 19th-Century Historical Indo-European Linguistics (Bloomington: Indiana U. Press, 1967); George Cardona, Henry M. Hoenigswald & Alfred Senn, Indo-European and Indo-Europeans (Philadelphia: University of Pennsylvania, 1970).
Similarly, linguists theorize that some 5000-9000 years ago, before recorded history, the Proto-Indo-European language splintered into dialects, one of which was Armenian. Armenian is nearly unique among the Indo-European languages in that Armenian is a separate branch of the Indo-European language family, unlike French and Spanish, which have a common intermediate source. Its immediate source is Proto-Indo-European itself. The Armenian language dates to the early period of Indo-European differentiation and dispersion some 5000 years ago, or perhaps as early as 7,800 years ago according to some recent research,14 that eventually spread Indo-European speakers throughout Eurasia from Iceland to India.
This fact about the genesis of the Armenian language is consistent with several competing theories of the genesis of the Proto-Indo-European language family and its earliest speakers.15
15J.P. Mallory, In Search of the Indo-Europeans: Language, Archaeology and Myth (London: Thames and Hudson, 1989) 143-147. On the ambiguity of archeological and linguistic evidence generally, see, e.g., Ward Goodenough, “The Evolution of Pastoralism and Indo-European Origins,” 253-266 in Cardona, Hoenigswald & Senn, Indo-European and Indo-Europeans (Philadelphia: University of Pennsylvania, 1970) 262.