Short answers, pulled from the story.
The first written evidence of an Indo-European language appears in the 1700s BC with the Anitta text. This fragmentary evidence was found in the administrative records of the Assyrian empire at the Anatolian colony of Kültepe. It contains isolated Hittite words and names embedded in texts written in Akkadian.
Sir William Jones delivered a lecture to the Asiatic Society of Bengal in 1786 declaring that Sanskrit, Greek, and Latin shared a common source. This statement became the foundational moment of historical linguistics. Earlier observations by Thomas Stephens in 1583 and Filippo Sassetti in 1593 failed to spark a movement.
The academic consensus points to the Pontic-Caspian steppe as the geographical origin of the Proto-Indo-European language. This region stretches across what is now Ukraine and Southern Russia. It is associated with the Yamnaya culture and other related archaeological groups during the 4th and early 3rd millennia BC.
The division of the family into ten major branches reflects the historical splitting of the ancestral language into distinct lineages. These branches include Albanian, Armenian, Balto-Slavic, Celtic, Germanic, Hellenic, Indo-Iranian, and Italic. Some branches like the Anatolian languages diverged early while others like the Germanic languages underwent radical sound changes.
Today, the Indo-European language family is spoken by over 3.4 billion people. This represents 42% of the global population, making it the most widely spoken language family in human history. English, Spanish, Portuguese, Russian, Hindi, Bengali, Punjabi, French, and German lead the list of native speakers.