the pentatonic scale: fundamental to all humans?

Bobby McFerrin gives a demonstration showing how an audience will naturally sing the pentatonic scale:



Or do they? Certainly, the scale they sing is the pentatonic. But McFerrin gives his audience three of the five tones, and the other two are merely whole steps from the previous tone. If he had let the audience continue up the scale on their own after he gave the first two notes, would they have sung the pentatonic, or would they have sung a diatonic scale? I don't think it's clear that the pentatonic would have naturally emerged without McFerrin's guidance.

But on another level, perhaps McFerrin has a point. Everywhere he goes, he says, people "get" the pentatonic scale. No other scale is globally recognized. Is the pentatonic hardwired into the human brain?

Hat tip to Good Math, Bad Math, which has a great discussion in the comments.