Historically, grains were a much poorer source of gluten than they are now. Through selective breeding and through milling processes that refine flour, wheat flour is now 13 to 23% gluten, depending on a number of factors, with whole grain flour being nearer the lower end of that range.

In addition, wheat generally and gluten specifically have become ubiquitous in the foods we eat. For example, soy sauce, which can easily be made gluten free, is often mainly wheat nowadays, especially the Japanese varieties of soy sauce. In the past, a person's gluten exposure was probably comparatively low and, combined with shorter life expectancies, gluten allergies were not as problematic.

Today, with wheat being in all sorts of foodstuffs, gluten allergies are becoming increasingly common, especially among middle-aged and elderly people. Our systems simply become so overwhelmed with gluten that the allergic inflammatory responses become a source of serious illness in some people. When coupled with the malabsoprtion syndrome that accompanies it, since an inflamed, damaged intestinal system absorbs poorly, vitamin deficiencies (especially vitamins E, D and K) gluten allergies cause real illness in many people. (italics mine - rjs)

Such illnesses probably remained sub-clinical in people in previous centuries but now, aided by enhanced severity, we better understand what's happening and we are better able to diagnose the trouble.

As for peanuts, just think of how peanuts have become readily available the world over and how they are contained in all sorts of foods, now. Historically, peanuts were a local food that formed a small part of the diet for people in areas near where they were found. In ways similar to what I mentioned above, peanut allergies are much more common and much more severe than ever before.

written by user "duh P3rf3ss3r" on slashdot.