What happened to drive the explosion of culture in the Upper Paleolithic?

This is a puzzle that may throw light on the emergence of human consciousness. The problem is presented by R. Quinlan nicely here.

One hypothesis is that true symbolic thinking emerged at this time (40,000 years ago), enabling all that cultural creativity. Perhaps here we see an emergence of imagination qua 'metarepresentation' in Baron-Cohen's sense. On my account this would have been associated with the emergence of consciousness. And we see a close link with autonomy and consciousness here. (Perhaps there could be an embodied cognition argument here, connecting these two?) Prior to this time, there was - I propose - no human conscious, rational autonomy, only biological automation. What the data suggests to me is that since cranial size is not correlated with the cultural explosion (see the lower graph), cultural interactions were essential for the emergence of consciousness. Consciousness is not a biological given, but its biological potentiality needs to be teased out through cultural learning, much as a child’s awareness of the world requires cultural learning. So I suppose I’m more in favour of the cultural ‘critical mass’ hypothesis that is mentioned.