It was a period of Megalithic culture, the appearance of the first significant economic stratification, and probably the earliest presence of Indo-European speakers.
The economy of the Chalcolithic, even in the regions where copper was not yet used, was no longer that of peasant communities and tribes: some materials began to be produced in specific locations and distributed to wide regions. Mining of metal and stone was particularly developed in some areas, along with the processing of those materials into valuable goods.
Earlier, from c. 5000 BC to 3000 BCE, use of copper began in the Balkans, Eastern Europe, and Central Europe. From c. 3500 onwards, there was an influx of people into Eastern Europe from the area east of the Volga (Yamnaya culture), creating a plural complex known as Sredny Stog culture. This culture replaced the Dnieper-Donets culture, and migrated towards the Northwest to the Baltic and Denmark, where they mixed with natives (TRBK A and C). This may be correlated with the linguistic fact of the spread of Indo-European languages; see Kurgan hypothesis. Near the end of the period, another branch would leave many traces in the lower Danube area (culture of Cernavodă culture I), in what seems to be another invasion.
Far more work has gone into reconstructing PIE than any other proto-language, and it is by far the best understood of all proto-languages of its age. The vast majority of linguistic work during the 19th century was devoted to the reconstruction of PIE or its daughter proto-languages (such as Proto-Germanic and Proto-Indo-Iranian), and most of the modern techniques of linguistic reconstruction (such as the comparative method) were developed as a result.
PIE is hypothesized to have been spoken as a single language from 4500 BCE to 2500 BCE during the Late Neolithic to Early Bronze Age, though estimates vary by more than a thousand years. According to the prevailing Kurgan hypothesis, the original homeland of the Proto-Indo-Europeans may have been in the Pontic–Caspian steppe of eastern Europe. The linguistic reconstruction of PIE has also provided insight into the culture and religion of its speakers.
As speakers of Proto-Indo-European became isolated from each other through the Indo-European migrations, the regional dialects of Proto-Indo-European spoken by the various groups diverged from each other, as each dialect underwent different shifts in pronunciation (the Indo-European sound laws), morphology, and vocabulary. Thus these dialects slowly but eventually transformed into the known ancient Indo-European languages. From there, further linguistic divergence led to the evolution of their current descendants, the modern Indo-European languages. Today, the descendant languages, or daughter languages, of PIE with the most native speakers are Spanish, English, Portuguese, Hindustani (Hindi and Urdu), Bengali, Russian, Punjabi, German, Persian, French, Marathi, Italian, and Gujarati.
Asterisks are used as a conventional mark of reconstructed words, such as *wódr̥, *ḱwṓ, or *tréyes; these forms are the reconstructed ancestors of the modern English words water, hound, and three, respectively.
