Dante, the Italian author, was sort of a linguistic Darwin. He held a heretical theory. Europe’s languages, he thought, had not been made in a single moment, in a biblical Babel, but had evolved. With the care of a Victorian naturalist, he thus split Europe’s languages into families by their words for "yes": those who lived in southern France and said "oc" spoke a "Langue d’oc". 

    He was spot-on. Four centuries later, a British judge and polyglot called Sir William Jones arrived in Calcutta and was struck by the similarities between Latin and Sanskrit words for terms such as house (domus, dam) and god (deus, deva). Clearly they had "sprung from some common source, which, perhaps, no longer exists". The world’s languages were not a Babel but a brotherhood. 

    Proto, a new book by Laura Spinney, a journalist, offers a biography of that brotherhood—or rather its parent. For Jones’s "common source" now has a name: "Proto-Indo-European" (PIE). It was first spoken by as little as a few dozen people around the Black Sea then, roughly 5,000 years ago, spread with rapidity "from Ireland to India". Today, its offshoots include Irish, Hindi—and more or less everything in between. Almost half of the world’s population speaks a descendant of it. 

    PIE is long dead, but traces of it remain caught, like insects in amber, in modern languages, allowing academics to bring it back to life. Scholars know, for example, its speakers found visitors irritating: the PIE word "ghostis" gives English not just "guest" but "ghost", and Latin its word for "host" but also "enemy". 

Internet: <https://www.economist.com>(Adapted)