Homo evolved from the Australopithecines in eastern Africa, east of the Great Rift Valley. Some 4 million years ago, 4-foot tall Australopithecines, with prognathic snouts, small 450 cc brains, but the first bipedal (upright) primate, started spending less time in the trees and more on the ground, consuming a nearly pure vegetarian diet, existing on a wide variety of wild plants. They likely had large colons and smaller small intestines to accommodate the large quantity of bowel flora required to digest the otherwise indigestible polysaccharide fibers of their diet.
The first hominid that most anthropologists regard as the first Homo species was Homo habilis with slightly larger brains than Australopithecus, upright bipedal gait, a probable scavenger of animals. They likely observed the true predators, the ones with big canine teeth and claws like lions and leopards, tackle other animals, successfully killing and consuming them. After these predators were sated, Homo habilis noticed that the skull containing the brain and the bones containing edible marrow remained, along with whatever other fragments remained. Our Homo ancestors therefore scavenged what the true predators left behind. We learned that stones were useful tools to crack open the skull to access the brain, or to get the marrow in the bones.
Consuming animal flesh and learning to use tools as hammers, then knife edges, spears, and hatchets, allowed us to hunt and kill our own game. The bigger the game, the greater the danger, the greater the advantage of communication, which led to the development of language and the uniquely human vocal apparatus. The next Homo species in the evolutionary sequence was Homo erectus, a wonderfully successful strain of hominids who became masters of stone tools and the methods of the hunt, including trapping and herding, with the capacity for group hunt, cooperation, and communication.
In the evolutionary sequence of the Homo species, consumption of animal flesh, the development of tools, and the need for communication and collaboration all led to the progressive growth of brain size. As brain size increased, pelvic size could not keep pace and Homo newborns were born incompletely developed, requiring an extended time after delivery before achieving independence, much longer than other primates. The prolonged nature of human child rearing enhanced the enculturation process.
The sequence continues with the evolution of Neandertalensis and Cro Magnon, the latter being the first of the Homo sapiens, the forerunners of modern humans, appearing some 180,000 years ago. Brains volumes reached a height of around 1600 cc, teeth were virtually free of decay and deformity, with consistent evidence for nutritional adequacy with absence of signs, for instance, of iron deficiency or malnutrition. (The Wikipedia image at left shows the largest brained Homo that ever lived, Cro Magnon.) While life for early Homo certainly had its challenges, such as nematode infestation from poorly-cooked fish, or traumatic injury (leg fractures were uniformly fatal), malnutrition was not generally a problem for Homo. Pre-Neolithic life was, from a nutritional viewpoint, quite good . . .
That is, until around 10,000 years ago when Homo sapiens first added grains. The hunter-gatherer cultures of the Fertile Crescent added wild einkorn and emmer wheat. The inhabitants of southeast Asia added rice that grew wild. The Native Americans living in the southeastern coastal North America, MesoAmerica, and the west coast of south America added maize. The inhabitants of central Africa added millet and sorghum. (Of course, the timeline of grain incorporation is not quite as clean as this. Maize, for instance, gathered and then cultivated in what is now modern Peru something like 4000 years ago. For the sake of simplicity, we will call it roughtly 10,000 years Before Present.) What happened to Homo sapiens who added grains? The anthropologists tell us that grain-consuming Homo:
- Experienced an explosion of tooth decay. While tooth decay was rare among scavenger-hunter-gatherers, it became commonplace in grain consuming humans. Tooth decay was accompanied by tooth abscess and tooth loss.
- Shrinkage of the face and jaw - The gruel or porridge that grains commonly yielded meant less dependence on vigorous mastication. As the face and jaw shrunk, teeth also shrunk but did so inadequately, commonly leading to tooth crowding (thus braces in kids today).
- Iron deficiency - Anthropologists look for porotic hyperostosis or cribra orbitalia, skull evidence of inadequate iron intake or overexposure to blockers of iron absorption (e.g., phytates in grains). (Nematode infestation can add to the effect.)
- Malnutrition - Evidenced by horizontal ridges in the incisors and canine teeth.
- Reduction in stature - Height was reduced by several centimeters. Bone diameter (e.g., femur diameter) was likewise reduced, what the anthropologists call reduced "robusticity."
- Reduction in brain size - While the cause-effect connection is uncertain, roughly coincident with grain consumption, brain size decreased by 11% - a first in the evolution of Homo.
(Interestingly, the only exception to the above observations are southeast Asian cultures who consumed rice, arguing that rice is somehow different.)
That's as much as can be inferred from the remains of humans dating back that far. We unfortunately cannot reconstruct soft tissue diseases like colon cancer, heart disease, or dementia. Nonetheless, one pattern is clear: When humans first incorporated grains into their diet 10,000 years ago, corresponding to less than 0.4% of the time Homo species have walked the earth, we suffered substantial downturns in health evidenced by tooth decay, deformity, and deficiencies.
Ancient grains were an expedient, a convenience, a dietary patch in times of deprivation, or the means to increased accessibility that permitted social differentiation away from an egalitarian society. Of course, these humans consumed wild grains, not the modern grains that we have today, courtesy of agribusiness. It's much worse for us.
Comment: While we cannot attest the veracity of Dr. Davis' evolutionary theory, it is true that prior to the Agricultural Revolution, humanity hardly knew any dental or modern health problems. For more information, read our forum discussion Life Without Bread.