Re: History of Black Belt?
Well maybe the question doesn't quite fit the history - as it assumes that a "black belt" meant to recognize commitment. Perhaps, way back when (whenever that might be), commitment wasn't in so much need of recognition - it just was (unlike today where it comes with all kinds of conveniences and all kinds of considerations). I think you might want to be asking, "When did the black belt get the meaning of 'expert'?" That probably happened right from its inception or right near there - when its existence made it possible to mark those who do not have one as "less skilled."
Or a better question might be: "When does a 'black belt' come to mean more about commitment and less about expertise?" Answer: When you mature enough in your training to realize the color of your belt and the title of your rank don't mean crap.