Short answers, pulled from the story.
Mainstream scholars place the Proto-Indo-Europeans in the Pontic-Caspian steppe during the Late Neolithic period. This region extends from northeastern Bulgaria and southeastern Romania through Moldova and southern Ukraine into the Northern Caucasus of southern Russia and reaches the Lower Volga region of western Kazakhstan.
Migrations occurred during the third millennium BCE coinciding with the taming of the horse. A modified form by J. P. Mallory dates migrations to around 3500 BCE without insisting on violent nature.
Ancient DNA studies have identified haplogroups R1a and R1b as markers of steppe population expansions. All Yamnaya individuals sampled by Haak et al. belonged to the Y-haplogroup R1b, while a large study published in 2014 by Underhill et al. analyzed over 16,000 individuals across 126 populations.
T. V. Gamkrelidze and V. V. Ivanov published work in March 1990 supporting this view that Proto-Indo-European was spoken during the fourth millennium BC in the Armenian Highland. David Reich argued in 2018 that the most likely location might be south of the Caucasus Mountains.
Philologist Martin L. West once stated that if an Indo-European language existed, a people who spoke it must have followed. Scholars analyze ancient languages like Latin and Sanskrit to deduce features of the original tongue and identify terms for domesticated cattle, horses, and dogs within the reconstructed vocabulary.