Why have allergies (especially severe ones) not been wiped out by natural selection?
In: Biology
you would need 3 things for that: allergies would need to be caused by genes, you would need to let all people die (before fertility) from allergies, and you would need to wait many many generations.
Allergies have become much more common in the last 50 years, but almost only in developed countries. We don’t quite know why that is the case, but the change happened much too quick for it to be purely genetic. This is therefore strong evidence that being allergic mainly isn’t a genetic precondition but has an environmental or lifestyle trigger(s). One theory is that our good hygiene today makes the immune system “bored” and trigger happy.
The immune system has to find a delicate balance: It has to be very aggressive to get rid of pathogens very quickly, but it must not be so aggressive that the immune response does more damage than the stuff that caused it (as is the case in severe allergies). The optimal aggressiveness of the immune system might still include some “false alarms”. If the sensitivity of the immune system were reduced so far that allergies (“false alarms”) never happened, perhaps many more people would die of infections than would be saved by not dying of allergic reactions.
Modern medicine is why. Natural selection isn’t as much of a determining factor on the passing of genes as it used to be.
Because humans with severe allergies can survive long enough to reproduce. Natural selection isn’t a mechanism it’s an explanation for why some traits survive and others dont
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