I think the "It's a blunder" view is simplistic, but so is, "It's wonderfully adaptive!" I think like the sensation of pain, or itch, it can be both. When it's

I think the "It's a blunder" view is simplistic, but so is, "It's wonderfully adaptive!" I think like the sensation of pain, or itch, it can be both. When it's working well, in moderation, and your environment is stable, you're going to be ok. If one of those elements goes awry, then bang. Being slightly allergic to something noxious makes sense, but being violently, potentially fatally allergic to a foodstuff? No...