I suggested other reasons than exchanged foods - it is because the dexterity is already present in those muscles due to talking and chewing in my opinion. I don't think the dexterity of your mouth muscles have evolved significantly in the last century. It is an ability that is a indirect benefit from other evolved traits.

Insight obtained from introspection or evolution in the 100 year scale will be mostly psychological/cultural. If you want to understand the big picture including physical justification you need to look at the large time scale perspective because it takes much longer for those changes, psychological and cultural justifications are dependant on the physical. Maybe that's too "booky or sciency" of a perspective, but I don't think so.