Well, "yes" and "no" are (or should be) only a part of a more (logically) complete answer that is usually implied and therefore not mentioned. Derived from your

Well, "yes" and "no" are (or should be) only a part of a more (logically) complete answer that is usually implied and therefore not mentioned. Derived from your example: "(Are you) hungry?" - "Yes(, I am hungry)!"/"No(, I am not hungry)!" I assume that the adverbs "yes" and "no" initially occurred as optional parts of an answer (only to later cast their supplementary part of the answer as the optional one). Curious enough, now when I'm thinking about it, I remember utterances with the usage of "yes" in the questions themselves (especially on some immigrants) - like "Hungry, yes?" I wonder what will this evolve into down the road...