On that - DH's gastroenterologist has said there's interesting stuff coming out about nut allergies (and coeliac disease and other IBDs) that suggests that the same part of the immune system that causes them is the one that used to deal with intestinal parasites like worms and nasty bacteria. Because of our love affair with triclosan and other antibacterials, these have been wiped out, but that part of the immune system remains. It's effectively sitting around bored, so starts to attack what it decides are foreign proteins, and this frequently happens to be nuts, eggs and shellfish. And THAT'S why it didn't occur in our generations - we weren't as obsessively clean.