For instance Spaniards (ethnic Visigoths) have near-total immunity to bad pork, whereas Jews (Jewish Diaspora, ethnic Jews) are very vulnerable.
Think of it this way: if there was a public service announcement by the early Jews, where would they write it down?
Visigoths probably drunk much more alcohol than Jews, which is a good disinfectant. In the old times it was even part of the soldier rations in some armies.
Some Visigoths converted to Islam and migrated to Morocco, but even after their conversion they still had a reputation of heavy drinkers.
For 10 years I was a pescetarian, until one time I tasted a beef carpaccio, and it was both edible and tasty (before that I wasn't even thinking about meat as a food). So I started eating raw meat dishes like steak tartar, but I always drunk a shot of something strong for safety, until one day I understood that it's unnecessary.
But like a Spaniard eating nearly raw pork doesn't die. Extrapolate for bad pork, he'll spit it out if it's bad.
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And since when does your one-cent Google search trump my traveling to Spain in person?
I'm afraid I don't see the connection between innate immunity and service anouncements or writing things down, but its probably me being thick even though I'd like to understand.
In America it's irrelevant, the bacon is pre-cooked to high standards and comes from good sources. Partly because secular Jews eat that pork having no cultural norms around it, just driven by it being forbidden. They're vulnerable.
It's genetic, just like a certain tribe of Pacific Islander developed a partial immunity to prions, because they sometimes ate human central nervous system. It's genetic.
Survival of the fittest.