Language started with emotional signaling. That's the thesis of a new book, The First Idea: How Symbols, Language, And Intelligence Evolved From Our Primate Ancestors To Modern Humans, by Stanley I. Greenspan and Stuart G. Shanker.
Lived emotional experience is key to language learning, the authors suggest. "Mathematicians and physicists may manipulate abstruse symbols representing space, time, and quantity, but they first understood those entities as tiny children wanting a far-away toy, or waiting for juice, or counting cookies. The grown-up genius, like the adventurous child, forms ideas through playful explorations in the imagination, only later translated into the rigor of mathematics."The book is very ambitious, and I don't think we'll ever know where language came from, but this sounds like a more fruitful line of thinking than Chomsky's deus ex machina "language gene" mutation.