Why have allergies (especially severe ones) not been wiped out by natural selection?
In: Biology
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.
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