Proto-Indo-European PIE is the mother of almost all the languages of Europe. The exceptions being Basque (Euskara) which comes from Mars and Finnish (Suomi), Estonian (Eesti) and Hungarian (Magyar) which come from somewhere in North-Central Asia and are members of the Finno-Ugric family of Uralic languages. That's Uralic as in Ural Mountains. Such diversity make life infinitely more interesting for those who travel in Europe. But the rest of us speak dialects of the same language which spread from Central Central Asia 5000 years ago.
How do we know this? Largely because of the work of August Schleicher a German linguist &word-lover who was born on this day in 1821. His magisterial, obsessive Compendium der vergleichenden Grammatik der indogermanischen Sprachen (1861) a Comparative Grammar of Indo-European Languages was das Buch on the subject for the rest of the century at least. Comparative linguistics is an interesting science, especially helpful when you're living with someone who speaks a different language - you can, with a little imagination and a large vocabulary, try synonyms and archaisms to get to a mutual understanding. We don't, for example, use the word porte for a door but the fellow who minds the door is still a porter.
Schleicher's theory of language was explicitly evolutionary, and thought out (according to Schleicher) before he ever read Darwin's contemporary theory of biological evolution. Languages are born by fragmentation from a common ancestor in the way we believe that many biological species arise by becoming separated from the main population and changing to suit their novel situation. But a lot of biological change is driven, not so much by natural selection, but by more-or-less random could-go-either-way changes. This is especially true when the breakaway group is small. Every native Central South American (Olmecs, Aztecs, Maya, Inca, Yanamami, Zapotec, Guarani) is blood-group O for example - presumably because the small group of hunters who schlepped across the Bering land-bridge to Alaska were all related and all group O. Their descendants walked all the 15,000km way to Tierra del Fuego over the next 10,000 years. Schleicher was the first person to think of representing relationships among languages as a family tree - a technique we use all the time to compare the sequence of genes and proteins.
Schleicher and subsequent PIE researchers have deduced the location of the original PIEs from the words that all the descendant languages have in common. Many of these were gathered together into what has become known as Schleicher's Fable:
Are you sitting comfortably?
Avis akvāsas ka
Avis, jasmin varnā na ā ast, dadarka akvams, tam, vāgham garum
vaghantam, tam, bhāram magham, tam, manum āku bharantam. Avis akvabhjams
ā vavakat: kard aghnutai mai vidanti manum akvams agantam. Akvāsas ā
vavakant: krudhi avai, kard aghnutai vividvant-svas: manus patis varnām
avisāms karnauti svabhjam gharmam vastram avibhjams ka varnā na asti.
Tat kukruvants avis agram ā bhugat.
Which being translated goes:
The Sheep and the Horses (Oves Equos-que in Latin)
[On a hill,] a sheep that had no wool saw horses, one of them
pulling a heavy wagon, one carrying a big load, and one carrying a man
quickly. The sheep said to the horses: "My heart pains me, seeing a man
driving horses." The horses said: "Listen, sheep, our hearts pain us
when we see this: a man, the master, makes the wool of the sheep into a
warm garment for himself. And the sheep has no wool." Having heard this,
the sheep fled into the plain.