Why after thousands of years of consuming alcohol and bread there are still people who are allergic or intolerant to alcohol and gluten?
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The environment hasn’t produced the conditions where one set of genes would be fitter than another in the context of consuming alcohol and gluten.
In an extreme case, let’s say the only viable food source was gluten bread – that is, that is the only food in the whole world that we can consume. Over time, those who can more easily digest gluten bread are more likely to live longer and reproduce, thus carrying their generic disposition to process gluten.
But in the real world, people can and will consume gluten bread. More importantly, they *also eat other foods*. You can survive without bread, and many cultures don’t eat bread as a staple. Thus, we’re not going to see a genetic shift to reduce intolerance to specific foods because they will live long and prosper by simply not consuming the foods they cannot eat.
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