I would assume that it was largely due to sexual selection. Once you have a primitive form of language and culture through imitation, the ones best at imitating others and best at entertaining, problem-solving etc. become the leader of the social group, and higher status means higher chance to mate. The reason I think it's sexual selection is that brain size more than tripled within some 3 million years or so in human evolution. And if there is a runaway process with huge (even exponential) growth, the answer is very often sexual selection (i.e. the peacock's tail).
Another crucial factor is that once a certain threshhold was passed, our brains became inhabited by memes. Imagine them like a certain configuration of wiring and neuron activity (level of weightedness) in the brain that somehow convey 'meaning'. A meme is a unit of information, the foundation for culture. Gene is to evolution as meme is to culture so to speak. And because memes don't need to wait for the next generation but can spread through means of language, books or now radio and the internet, we have another runaway process: culture. Thus our knowledge grows exponentially.
This led to the fact that our knowledge actually 'did catch up'. We don't need myths anymore, we can give sound answers, or sketches of such answers, to most philosophical questions that philosophers have failed to answer for millennia.