It's like trying to find a need... no, not a needle, something smaller than a needle, in a haystack, when you don't even know if you're in the right field.
Madness string 870
So many weird old religious rules started out as trying to keep unenlightened but highly religious groups alive, fed, and disease-free, and somehow we've hung onto so much of it. For another example, check out the origin of sacred cows.