- largest language family by number of speakers: ~3.2 billion
- branches: Germanic (English, German, Dutch), Romance (Spanish, French, Italian, Portuguese), Slavic (Russian, Polish, Ukrainian), Indo-Iranian (Hindi, Urdu, Persian, Bengali), Celtic, Greek, Armenian, Albanian, Baltic
- proto-Indo-European spoken ~4500-2500 BCE, likely in the Pontic-Caspian steppe
- spread through migration, horse domestication, and the wheel during the Bronze Age
- reconstructed through comparative linguistics: shared roots for kinship, animals, agriculture, numerals
- the Hittite, Sanskrit, Greek, and Latin literary traditions are all Indo-European
- English, the dominant language of the Information Age, belongs to the Germanic branch
- understanding language families reveals deep structure in human knowledge transmission