Evolutionary science has long viewed language as, basically, a fortunate accident--a crossing of wires that happened to be extraordinarily useful, setting humans apart from other animals and onto a trajectory that would see their brains (and the products of those brains) become increasingly complex.

But as Michael C. Corballis shows in The Truth about Language, it's time to reconsider those assumptions. Language, he argues, is not the product of some "big bang" 60,000 years ago, but rather the result of a typically slow process of evolution with roots in elements of grammatical...