When ideas go extinct, we all grow poorer. Half the world’s 7,000 languages now face extinction — a dramatic shift in human intellectual history. Our 21st-century world — replete with wondrous technologies — rests upon the foundation of all humankind’s prior wisdom and creativity. This human knowledge base is durable and, during 99 percent of human history, has been passed solely from mouth to ear. Yet it is fragile, mostly unwritten and vulnerable to forgetting.