Pretty simple question. I can't figure out why even an infinitesimal ability to consume gluten without inflammatory effects would not have been present and selected for once gluten became part of a regular diet. Could somebody clear this up for me?
I guess the way I'm seeing it is that when people started eating grains, even though they may not have had really deleterious effects until post-reproductive periods, those humans who experienced less severe deleterious effects would have been able to care better for their kids, or have more kids (well, men, since they don't pass out of the reproductive period), or what have you.
And, for the response that gluten has an impact "later in life," I have a question.
Do you contend that absolutely zero effects manifest themselves before reproductive age? That would be counter to what I'd expect, given the success stories of people who stopped eating gluten prior to being reproductively inept. Further, even if this impact occured after reproductive activity ended, you'd still be able to do things (gather food, care for young), so that those effected by gluten, and therefore unable to aid their families, would be less likely to see their genes spread.
Anyway, throw me some insight please.
Just about everyone can digest gluten well enough. Digestion is not the issue.
Gluten intolerance is an inflammatory, sometimes auto-immune response to the proteins that make up gluten. If you are celiac, you're having an auto-immune response, if you're just sensitive, your small intestine is being irritated by gluten proteins as they are broken down. That irritation can cause all sorts of systemic problems - people sometimes report allergies, random inflammatory diseases and other problems clearing up once they eliminate grains.
Unless you are celiac or severely sensitive to gluten, you will live and reproduce just fine. Even if you are celiac or severely sensitive, you might survive. There are plenty of people who find out later in life that they are celiac or gluten intolerant, after decades of dealing with the attendant gastro-intestinal issues. You don't need to be perfectly adapted to gluten to generate offspring, you just need to not get sick enough that you become unsuitable for mating (through death or general ill health). Just about everyone can swing that.
So it's not clear that gluten tolerance would be strongly selected for. Clearly celiacs and severely intolerant people might be selected out, but people who were just mildly sensitive and whose only symptom was a digestive problem would probably do just fine relative to their non-gluten sensitive compatriots.
edit in response to edit:
I wouldn't say that there would be ZERO effects - people would exhibit the same spectrum of issues that they do today, probably, with one end being complete inability to function while eating bread, and the other being either completely fine or with such minor issues that they simply don't crop up until heart attack age. Unless you are seriously intolerant or celiac, gluten will not cause acute problems. A lot of people see improvements in random problems when they drop gluten grains, but note how those people tend not to be dead or completely incapacitated - they're functional members of society who just have some minor chronic illness like allergies or digestive problems.
It's important to note that people prior to the past few generations generally endured a great deal more physical hardship as a matter of course. I can't find it now, but I read an article outlining the physical problems present in the American population around the time of the Civil War - they found cases of people working in the fields with huge hernias they were holding in with corset-like stomach wrappings. In the face of a pain tolerance like that, I doubt that the sniffles or the shits would really make that much of an impact.
All that said, it's entirely possible that gluten tolerance IS spreading around the population, something like lactose tolerance spread pretty quickly when it developed. Undoubtedly, there are some people who have better tolerance for gluten proteins than others.
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.
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.
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