"It is language, more than anything else, which makes us feel human," argues Crystal, a linguist. He begins scaling what he describes as "the Mount Everest of subjects", with how we learn language: "Babies pick it all up naturally, like breathing." Astonishingly, three quarters of the babies in the world learn more than one language. As well as how we  "the speaking animal"  master the spoken, written and now texted word, Crystal explores the origins of words and how they evolve. In an enlightening and entertaining celebration of language and linguistics, he also writes passionately about endangered languages. There are about 6,000 languages in the world, but this diversity is dwindling fast: half will be gone by the end of this century. Languages have died out before, but the scale of the current losses is unprecedented. Each one represents a unique embodiment of a people's culture and life-world: "Language allows us to talk about our experience of the world in a way that no other means of communication can."