The Human "Omnivore": a mythological beast
One of the most ridiculous and persistent false claims made by armchair nutritionists, meatarian propagandists, and even academics, who really should know better, is that the human species is an "omnivore"; that is, it should eat both plant and animal matter.
In general, this error is based on the accidental, or perhaps intentional, confusing of the verbs "to be" and "to do". If the human "is" a natural omnivore, then we should have ALL the physical and biochemical equipment that is NECESSARY to run down, kill with our bare hands, tear asunder, eat, and properly digest, RAW animal prey, just as ALL natural omnivores, or carnivores, do. Just looking at our bodies will conclusively prove that we do not have the claws or talons necessary to catch and hold animal prey, and we do not have the sharp, shearing teeth necessary to tear, not chew, animal flesh. We are not fast enough to outrun and catch animals. Natural omnivores or carnivores do NOT chew their eaten flesh, they tear it into chunks and swallow them whole. We do not have the "constant tendency for the last upper premolar and the first lower molar to engage and form long longitudinal opposed shearing blades (the carnassials)", which are a common characteristic of natural carnivores and omnivores.
No human cultural-carnivore kills its animal prey with his/her natural equipment, nor do they eat their animal prey raw. I have challenged countless meatarians to do so in the past 30 years, and NONE have shown the courage of their conceptual convictions and done so. Why? Simply because we are NOT an "omnivore". In fact, we have strong anti-killing instincts. Try to kill an animal with your bare hands to demonstrate this.
Any second-grader could differentiate between the verbs "be" and "do", yet this important distinction is totally ignored by cultural carnivores, and even academics with PhD's, who foolishly claim that because humans have been DOing cultural-carnivorism for a long time, that somehow (never explained) magically, we ARE "omnivores". They want to believe that DOing modifies BEing. They fail to understand the profound difference between Nature, and inviolable Natural Laws, and silly, self-destructive local cultural customs. By their absurd and faulty logic: because some humans DO murder, and because murder has existed throughout human history, ALL humans ARE born murderers.
If one wanted
to produce a logical test to see if the human was a natural omnivore,
the procedure would be:
Of course, this quite obvious test mechanism has not been established, and any unsupported references to human "omnivores", regardless of the source, are confirmations that only cultural whims are being reported, certainly NOT the imperative physiological and biochemical attributes.
For more detailed analysis of the human "omnivore" mythology, and the bizarre distortions of fact and logic necessary to make this false claim, we can look to the always-amusing, misologistic BeyondVeg website. This site is produced by a crackpot who, apparently failing in his personal efforts to become a raw-fooder, has stolen the title of one of my articles for his web domain name, and has gone on a rampage to attempt to discredit plant-based diets in general by applied pseudo-science. His state of mental dysfunction is demonstrated by his repeatedly claiming in a vegetarian/vegan discussion list that he could read my "emotions" with his modem, and his bizarre claims that John Coleman and I are really the same person. This is quite a feat, as John lives in England, and I live in Florida. Co-location, perhaps?
One hears hollow claims that since "Paleolithic man" ate flesh, that modern humans are somehow "adapted" to do so. In fact, a Paleolithic diet cult is being developed.
The "Paleolithic argument" runs something like this: The proto-human was indeed a frugivore (eating primarily fruit, such as modern chimps) 50 million years ago (MYA) to 2 MYA, when the "appearance of stone tools and cultures at this time" coincided with "increased meat-eating"[W1]. Well, that's the end of the argument, as its fatal flaw is revealed: the fact is that "increased meat-eating" occurred ONLY because of tool use, and since tools, including fire, are a product of culture, not Nature, cultural practices, such as those powerful self-destructive cultural practices of today, are totally unrelated to our natural nutritional needs, which are programmed at the genetic level.
Anthropologists' fantasies that humans commonly 'scavenged' dead, putrefying flesh left to rot by natural carnivores, or produced by the natural death of animals, are totally absurd. I would challenge any such confused academics to test their own theory by actually eating some rotting road-kill, raw, with their bare hands. With this simple test, said academic would immediately be forced to face reality instead of being hopelessly lost in vague, unsupportable, academic speculation. Let a group of academics who propagate this silly theory actually go to the field and fight off a pack of wild dogs or lions to get their leftovers, or chow down on a putrefying corpse crawling with maggots. Yummy!! The human is programmed at the genetic level to vigorously avoid rotting protein, and is particularly sensitive to such repulsive odors which produce instantaneous, powerful, gag and nausea reflexes in even the most stalwart meatarian. Yet, even 'educated' academics with PhD's can not deal with this simple and overwhelmingly obvious fact in their boundless zeal to reconstruct a long-lost past from infinitesimally small amounts of data; and worse, massage this virtually nonexistent data with their local culture's conditioned belief systems to produce wildly imaginative, yet obviously false, claims about the human being.
Although some cultural human may have, post-tool, consumed rotting animal flesh intentionally, the inherent repulsiveness of which was masked by the destructive, pyrolytic effects of fire, the fact is that the natural human would not have left any lingering evidence of its natural diet, just as the modern chimp does not leave any trace of its existence. Eat some fruit, drop the seeds on the ground, eat some leaves, eat some nuts -- where is the physical evidence that lingers for 10's or 100's of thousands of years?? None! So, all so-called Paleolithic "evidence" of human flesh-eating is merely a collection of self-selected, statistically-insignificant cultural artifacts, totally unrelated to our species' true nutritional needs.
Further, such physical evidence of human flesh-eating, such as tool-scarred bones or ancient fire pits, is found only in northern areas which are well outside of the natural ecological niche for our tropical ape species; thus, any evidence of cultural diets so remote from our proper ecological niche is totally irrelevant to any understanding of what the natural diet for our species is. This ecologically-relevant, and crucially-important fact is universally, and conveniently, ignored in any discussions of Paleolithic humans. Paleolithic (tool using) humans are not natural humans and are just as irrelevant as any modern cultural group and their modern self-destructive dietary practices.
Further, "Because of the considerably harsher conditions and seasonal variation in food supply, hunting became more important to bridge the seasonal gaps, as well as the ability to store nonperishable items such as nuts, bulbs, and tubers for the winter when the edible plants withered in the autumn. All of these factors, along with clothing (and also perhaps fire), helped enable colonization of the less hospitable environment." clearly admits that such humans were well outside of their natural ecological niche which would provide the proper nutrition for our species, thus they were forced to consume highly foreign, non-natural "foods" just to survive. So, it is obvious that any claims as to the applicability of the Paleolithic diet to any understanding of the natural diet for our species are totally, and unavoidably, bogus. They are shams firmly based on lies and intentional distortions. They are merely other examples of how "curiosity killed the cat". See the movie: The Quest For Fire for a little insight into the perils created by abandoning our ecological niche.
If one can get a meatarian propagandist to actually admit that these incredibly recent, human flesh-eating practices are only a cultural artifact, then the ruse becomes: "Yes, it is not natural, but we 'adapted' or 'evolved' to eating animal flesh and products". This is another blatant, yet annoyingly popular, lie, and it can not be supported by current evolutionary theory. Where, indeed, are our claws, fangs, beaks, or talons?
Evolution happens because of small, infrequent, random mutations in the genetic material: most mutations are neutral and are never expressed, some very small number may be "beneficial" in that they allow better functioning in the environment, and some very small number may be deleterious, such as those that produce "genetic diseases". There must also be some "selective mechanism" to produce more survival success in those with the "beneficial" mutation, or it will not propagate throughout the species to produce a species-wide "adaptation". So, what are the "selective pressures" or "selective mechanism" that would cause the numerous and large-scale changes in dozens of separate biochemical pathways involved in human digestion, transport, and assimilation of a diet so radically different in chemistry as an alleged "adaptation" from plant chemistry to flesh chemistry? Note that dozens of biochemical pathways must change simultaneously in the same individual for such an "adaptation" to occur. There are none. Because a faulty diet does not kill its proponents outright BEFORE reproductive age, there is simply no way to "adapt" to a diet radically different in chemistry from the natural one for that species, even IF the dozens of required changes magically occurred in one individual. This is admitted in the BeyondVeg site: "The foods that humanity originally evolved to eat and those we now eat in modern civilization are in many cases significantly different--yet our basic underlying genetic inheritance remains basically the same as it was before, and has evolved only very slightly since then. Thus, many of the foods we now eat are discordant with our genetic inheritance."[W2]
Not surprisingly, all such claims as to the unsupported human 'evolution' from frugivores to omnivores conveniently do not mention the fact that neither the necessary sharp tools (teeth, claws), digestive biochemistry, fleetness of foot, nor animal-killing instincts have co-evolved with the alleged 'evolution' to omnivore. Why did the concomitant, and quite necessary, tools NOT co-evolve? People distorting evolutionary theory to make the evolutionary omnivore argument fall silent on those points.
In bizarre self-contradiction, BeyondVeg uses this evolutionary analysis to claim that modern grains and legumes are not a suitable food, with which I firmly agree, but it simultaneously, and perhaps intentionally, does not apply this understanding to the obvious fact that the human simply has not "evolved" to successfully consume animal flesh or other animal products. The epidemiological evidence that eating animal products causes all the currently popular "degenerative diseases" is conveniently overlooked in the presentation.[E1, E2, E3, E4] It gets even more amusing: "humans ... are in a transitional state from omnivory to obligate carnivory."[W3] This foolishly claims that humans are 'evolving' from frugivores, through cultural (not natural) omnivores to pure (obligate) carnivores, like the cat, dog, eagle, or alligator! This by a PhD, who most certainly does not kill and eat his/her animal prey raw and with his own natural physiological equipment; but, perhaps, has the initial appearances of claws and fangs, and is indeed on the cutting edge of 'evolution', such as to have such remarkable insight?
On the B-12 issue, the self-contradictions continue. "Cats can neither synthesize B-12 nor absorb it from their gut; consequently they have become wholly dependent upon animal flesh as their source for this essential nutrient."[ibid] Let's see, they can't absorb it from their gut, but eat flesh and then absorb it from their gut?
There is hope for the vegetarian/vegan, however: "Regarding possible B-12 synthesis in the small intestine above the ileum, the consensus of scientific literature indicates any amounts that may potentially be produced are not significant or reliable enough to serve as a dependable or sole source for most individuals.[ibid] MOST individuals? That means SOME individuals do produce and absorb their own B-12; could it be that the cause in the ones who can not is based on the fact that their intestines are ravaged by the toxic byproducts of putrefying meat, and that a healthy intestinal system in a healthy human is a reliable source of B-12? The practical solution to any concerns about B-12 is a simple and inexpensive supplement; which, given the precipitously declining quality of commercial produce, would be useful insurance anyway. The claim: "...demonstrate the human metabolic need for animal-based foods" ignores the fact that B-12 producing bacteria are abundant in the exogenous environment.[E5]
Interestingly, "In one study of vegans ... the [source of B-12] was due to eating unwashed vegetables that had been grown in gardens containing intentionally manured soils, from which the B-12 came. Ironically, the manure in this case was their own excrement, which as pointed out above harbors bacteria that produce B-12 in the human colon--where B-12 cannot be absorbed. Not unless, of course, it is reingested as in the unintentional coprophagy occurring in this instance, so that it can pass back through the small intestine again to the ileum where B-12 is actually absorbed."[ibid] Of course, it is unknown just how this study differentiated between the B-12 molecules coming from bacteria in the human colon and the B-12 coming from bacteria in the soil. It also ignores the fact, know by olfactory experience among vegetarians/vegans who are not eating huge excesses of protein, and totally unknown among meatarians who are eating huge excesses of indigestible proteins, that vegetarian/vegan feces is devoid of the common, malodorous, toxic amino compounds commonly found in meatarian feces: indole, skatole, putrescine, and cadaverine.
"In summary, the absence of the ability of humans to absorb bacterially produced B-12 in the colon, and the evidence that strictly behaving vegans will show negative TCII-carried B-12 balance even when total serum levels are in the normal range, is indicative of the long evolutionary history of animal-based foods in our diet."[ibid] Actually, it is more likely an indication of the rather recent deadly cultural practice of dousing commercial food with boundless amounts of toxic pesticides and herbicides which will kill the normal B-12-producing bacteria, and everything else, in the soil, coupled with the rather recent cultural sanitary hysteria which, also, will eliminate exogenous B-12 from food.
 McGrawHill Concise Encyclopedia of Science and Technology, 2nd ed., p. 323.