I am not 100% sure that is accurate. I think the time frame you are referring to is relative to "cultivated" grains and legumes. I would suppose in the hunter/gatherer aspect of life there had to be plenty of opportunity to gather all sorts of seeds, including grains and legumes. It was only when people learned to cultivate such things effectively that they were able to reduce the nomadic lifestyle and be able to stay put. At that point they had an effective food source and animal proteins could punctuate the diet rather than be the mainstay. I believe neanderthal had a major meat diet, and a good 5000 calorie daily requirement. Talk about an expensive lifestyle. Brain activity is predicated on sugar, in theory having access to a lot of caloric staples probably allowed lots of intelligence gains.BTW: the grains were added to the human diet only 10K years ago - basically yesterday.
This raises a valid question, do the grains and beans even belong in the proper human diet?
Very well one can argue that the grains/beans don't even properly belong in our daily eat.
As well, one can argue that most modern deceases come from the excessive consumption of grain-based foods (ESPECIALLY refined grain-based foods. This is abnormal per the very basic human biology - human body is not really tuned well to consume lots of grain products.
What gets most interesting is the choices we have made in cultivated foods vs "weeds". I don't remember if it was in "Stalking The Wild Asparagus" or possibly one of his other books that Euell Gibbons discusses just these aspects of how some things we consider weeds are as healthy if not more so that the foodstuffs that we chose to propagate for our chosen foods. So many things grow in the wild that could have become cultivars, but most of them very few people (Except maybe Bear Grills) will even ever know what they taste like.
In general, I have to believe you about refined grain, and most processed foods in general. The farther away from what it looked like when it was alive the less valuable it is to you. Originally, much of processing was to facilitate storage. Also leading to some dietary freedom because you didn't have to gather food for today's meals today. And later, for transportation, so you could sail the ocean and not have to grow and grind your food on the ship, or live on fish alone.
Interesting thing, however, white enriched flour. Since white bread became such a staple of the diet, flour was chosen as the vehicle for folic acid. This was done specifically so that the folates necessary to prevent neural tube defects in infants could be included in the diet. When the health conscious started eschewing white bread in favor of whole grain goodness (not required to be enriched) or avoiding white flour at all... has raised some issues with increasing instances of such things and how to get folic acid specifically back into the diets of modern women. Similarly we have iodine in our salt, quite necessary for thyroid function, and necessary for the thyroid hormones... but guess what all of the sudden they are demonizing salt, and people stop eating salt.
Anyway, such dietary issues, and the failures of the "we know better than you do" nanny state and their silly food pyramids and so forth are always a favorite topic of mine. Imagine that, you would think I would practice a much healthier diet than I do, and not have nearly the amount of avoidable issues..