The now-extinct Tocharian language on a scrap of parchmentSakkmesterke/Alamy Proto Laura Spinney (HarperCollins (UK) Bloomsbury Publishing (US, 13 May)) A new book by Laura Spinney is rather tantalisingly called Proto, begging the question: proto-what? Prototype, the earliest version of a technology? Protoplasm, the stuff of our cells? Or even protoplanet, a small hunk of space rock with a big future ahead? The answer, in fact, sits above and across those words: Proto-Indo-European. This is the great original language from which English, among many other tongues, both alive and dead, derives. As Spinney puts it: “Almost every second person on…