Us modern humans, Homo sapiens, have walked the earth some 200,000 years. Our upright, bipedal, large-brained, and social hunter-gatherer predecessors, Homo erectus, walked the earth for nearly 10-fold longer, bridging the era when humans first began to eat animal flesh, whether via scavenging or hunting, and the relatively recent (500,000-700,000 years ago) harnessing of fire.
Before these two forms of Homo, we were preceded by Homo habilis (the “toolmaker”), believed to be the first to wield tools (remember the monolith scene in 2001: A Space Odyssey?), and by the varieties of Australopithecus, harking back to a creature more ape-like, with longer, curved fingers and toes, less of an opposable thumb, brains that were much smaller, vertically longer pelvises, and longer arms and shorter legs than more recent versions of Homo. All these forms of human and pre-human now reach back 10+ million years.
When was grain consumption, including wheat, added to the diet of humans? It wasn’t during the time of Austropithecus, nor was it during the reign of Homo habilis. Although the long-successful Homo erectus learned how to scavenge/hunt animal flesh, they did not eat any wild growing grains.
It wasn’t until the last 5% of time since modern Homo sapiens appeared that they learned how to first harvest wild, then cultivate, wheat–einkorn, of course. If we include the time of Homo erectus, then humans have consumed grains for around 0.5% of the time they’ve walked the earth.
My point: Given the relatively slow process of evolution, we need only look at the 2 millions years of eating habits of Homo erectus and the first 190,000 or so years of Homo sapiens to recognize that consumption of grains like wheat is a very recent change to the dietary habits of humans. For millions of years, humans evolved and survived without grains in any form.
Yes, harvesting of wild, then cultivated, grains provided the impetus for creating non-nomadic society and occupational specialization, a source of calories to supplement calories from animal products and plants. But is there any evolutionary or biologically plausible reason that we are now told that 60% or more of our calories should come from grains like wheat?