I just acquired the following, utterly charming bit of information (well, I think it's utterly charming, but I'm a total geek about things like this) -
Why do Jews traditionally eat gefilte fish on shabbat/holidays? Because according to religious law, you cannot separate the flesh of a fish from its bones during rest days - doing so counts as work, and thus is prohibited. Gefilte fish evolved as a way of allowing observant Jews to serve fish for their festive meals without violating this prohibition.
I am now fascinated by this sort of information. There are sociological, religious, etc. explanations for many, many kinds of dishes. Would you share your favourite story about how a traditional foodstuff, culinary practice, etc. developed??