We have already enough evidence to assume that such cliff does not exist. I can recommend the book „How language began“ by Daniel Everett, where he demonstrate

We have already enough evidence to assume that such cliff does not exist. I can recommend the book „How language began“ by Daniel Everett, where he demonstrates convincingly that our path to language, culture and consciousness was not a single switch, but evolutionary process. Recent research of cetaceans shows that their language and culture may overlap in sophistication with our ancestors.