I think it is likely that some genetic adaptation/natural selection has indeed happened in some populations towards gluten tolerance. However, a lot has changed in that last 100 years. The grains we eat have been highly bred and rebred and in many cases, genetically modified, such that they are far from what we spent thousands of years adapting towards. And most populations eat a LOT more than they used to eat. And much of that grain is now processed and bleached which is different from how we originally ate it. Plus we now add tons of sugar, fructose, high fructose corn syrup and other garbage on top of it. Plus the yeast strains we use now in bread are very fast acting and do not have much time to break down toxins like gliadin. Our technological and food production evolution has FAR FAR outstripped our gluten tolerance evolution. And with many people's metabolisms already badly damaged, even small amounts of the new alien grain strains are too much for them.

There is reason to believe that certain people are more adapted to digesting gluten proteins than others to various degree.

Example: celiacs have severe reactions to gluten. They are on the extreme side. I have a reaction that is not acute but is definitely present (after a few days of eating gluten proteins I get serious eczema and other sores). My wife has no visible problems eating gluten. She is of European descent. I am of Asian descent. Asians have not had very long to adapt to gluten since rice does not contain gluten. Europeans have had a longer time adapting to gluten, not to mention many primitive agriculturalists who have developed grain technology (fermentation, etc) that can reduce the toxicity of grain proteins and enzymes. This is typical of primitive agriculturalists. Andes cultures in South America consume very toxic potato varieties after a long and involved processing. In other words, humans have adapted our foods to suit us. In the meantime, we continue to evolve to optimized gluten protein digestion. Its a long process of attrition.

Remember, when humans first made grains a staple in caused brittle bones, tooth decay, greater susceptibility to disease, and stunted growth. That was 15-20,000 years ago. Contrast that with today's grain eating Europeans and Northern Africans. Tall, healthy, strong bones and straight teeth. They have clearly adapted to grains and gluten proteins. Check out images of Weston Price's primitive peoples. Clearly, they eat grains and are very healthy. But they eat grains processed primitively through soaking and fermentation. This is why Weston Price advocates eating grains only if sprouted or fermented.

Hope that sheds some light on the complicated process of human evolution.

It is important to remember that for every human cell that constitutes your body, there are 10-100 microbial cells--this human/microbe partnership, sometimes referred to as the human "superorganism", is part and parcel of evolution. We are only recently beginning to understand and explain the symbioses that stretch at least as far back in time as single-celled organisms themselves. It is widely held that the mitochondria present in all multicellular organisms are descended from a single-celled organism that was "eaten" (but not destroyed) long ago by another microbe--and we and all animals, plants and yeast are the descendants of the resulting organism.

A lot of what we know and are learning about gluten-induced inflammatory conditions indicates a role for our gut microbial ecology. Celiacs, for example, can be "latent" (they have "celiac genes" but don't have symptoms) for many years, until a course of antibiotics or a viral infection prompt some change that we don't understand, after which they begin having classic symptoms and eventually the defining symptom, villous atrophy. A recent letter in Science suggested a model for understanding Crohn's disease involving a complex interaction involving viral infections, irritants, and normal gut bacteria. See here: http://stm.sciencemag.org/content/2/43/43ps39.abstract

We have only begun to understand why gluten may cause problems in some people. To look for an adaptive explanation, especially one that is absent any scientific evidence or inquiry, is premature.

Yours is a well-intentioned question--but to answer it directly is to apply a very narrow model to an extremely complex evolving system, in which, for example, there are basically no "traits" (e.g. "gluten tolerance", "eye color" etc) that can be acted on by selective pressures independently of other traits.

I caution everyone against using facile interpretations of adaptation that amount to "Just So Stories." These tend to amount to unsupported "explanations" of why things are as they are that reinforce hidden cultural/historical/socioeconomic/medical/other established narratives and biases.

It's an understandable and extremely common mistake, but be VERY careful! This is the very same trap the eugenicists fell into, using fallacious and unscientific narratives to justify horrifying crimes against humanity.

These malformed arguments still deform the perspectives of too many scientists and medical researchers and practitioners. Adaptation is attractive because it is such a powerful explanatory tool--but it can only be invoked with scientific credibility after long and careful study, and discussion and debate in the context of academic peer-review. I don't mean to sound elitist, and I hate academic elitism, but it's dangerous to hand-wavingly invoke adaptation as a "scientific explanation" of the way things are.

Further reading: adaptationism, evolutionary constraint (natural limits on the strength of selection), Eugenics, and adaptationist fallacies in evolutionary psychology.

I hope that helps!

A good article delightfully titled "How to keep feces out of your bloodstream" http://www.fourhourworkweek.com/blog/2010/09/19/paleo-diet-solution/ by Tim Ferriss and Robb Wolf graphically describes what happens to your gut when anyone eats this stuff. Obviously everyones mileage will be different but the upshot is no one is immune to its effects irrespective of how many generations you have had to adapt.

I would say that one also needs to consider the wide spread use of pesticides, fungicides, and other chemicals as well as the genetic manipulation of grain seeds. Focusing primarily on gluten has been short cited by the scientific community as a whole.

Give it time. We're in the middle of the evolutionary process. We're just smart and observant enough to notice it happening around us.