My intuition tells me that human evolution grokked language. Maybe like GPT it very quickly went from being complete gibberish to freakishly coherent. A handful of words and grammar rules leads to remarkable complexity. But that's a guess.
A bunch of workers from various countries are thrown together on a ship or some other international workplace and they develop a pigeon dialect of all their different predominate languages mashed together.
That pigeon develops and gets used for workplace needs but then these workers have families and their kids pick up that same pigeon language to talk with their friends except they need to talk about everything not just workplace stuff so they develop and advance the pigeon language and it goes from a basic rudimentary language into a full featured and complex language in a single generation even with just a few hundred speakers.