A recent study has led some researchers to think that the possibly modern phenomenon of allergies has been created by something humans living in the last 100 years lack that almost every human being in previous centuries has had plenty of:
That's right, there is a hypothesis being tossed around that in species that evolve with constant contact with a common parasite, the parasite and host species may evolve a body chemistry that actually needs both organisms present to function properly.
In other words, last week when my sinuses were manufacturing enough mucus to supply the entirety of the third world, and my throat was threatening to shred under the constant traffic of postnasal drip, all I needed was a good case of hookworms. The modern obesity epidemic? A lack of tape worms. Overpopulation on the Indian subcontinent? Eradication of the malaria parasite. The domination of east African athletes in long-distance running? A deficit of guinea worm infections.
Actually, the evidence suggesting that allergies could be caused by a missing parasite is interesting, but I wouldn't go out and get myself infected just yet. After all, even if we are missing some parasite that completes the part of our body chemistry needed for a perfectly functioning immune system, we'd have to decide if allergies (including the increasingly common killer reactions like those some have to peanuts) are worse than whatever the worms do to us. After all, we got rid of the worms way back when for some reason. I just don't know what that reason is. I've never actually had them to really understand it.