One ancient language transformed our world. This is its story.

"Star. Stjarna. Stare". Thousands of miles apart, people look up at the night sky and use the same word to describe what they see.

Listen to these English, Icelandic and Iranic words and you can hear echoes of one of the most extraordinary journeys in humanity’s past. All three of these languages – and hundreds more – share a single ancient ancestor.

Five millennia ago, in a mysterious Big Bang of its own, this proto tongue exploded, forming new worlds as it spread east and west. Today, nearly half of humanity speaks an Indo-European language. How did this happen?

In "Proto", acclaimed journalist Laura Spinney sets off to find out. With her we travel the length of the steppe, navigating the Caucasus, the Silk Roads and the Hindu Kush. We follow in the footsteps of nomads and monks, Amazon warriors and lion kings – the ancient peoples who spread these tongues far and wide. In the present, Spinney meets the linguists, archaeologists and geneticists racing to recover this lost world. What they have discovered has vital lessons for our modern age, as people and their languages are on the move again.

"Proto" is a revelatory portrait of world history in its own words.