@davep
We don't really know, do we?
From that publication, all we know it's that they make the rocking world go round.
We should take note of the word 'rocking' here. Is that to denote another world, or is it perhaps a previous version of the world? One without fat bottom girls perhaps.
In the latter case, FBGs might be considered a type of lubricant, which prevent the world from coming to a screeching halt.
More research is necessary to determine this.