To use terms that are linked to gut morphology, humans are either faunivores [meat-eaters] or frugivores with specific (evolutionary) adaptations for the consumption of animal foods. This, of course, means that humans are not natural vegetarians. A short summary of some of the evidence supporting this follows (the material below was discussed in depth in earlier sections of this paper).

• The fossil record. Approximately 2.5 million years of human omnivory/faunivory are apparent in the record, with genetic adaptation to that diet the inevitable and inescapable outcome of evolution. The supporting evidence here includes isotope analysis of fossils, providing further evidence of consumption of animal foods.

• Comparative anatomy of the human gut. The best scientific evidence available to date on gut morphology--analyzed using two different statistical approaches--shows evidence of adaptations for which the best explanation is the practice of faunivory. (Faunivory as an explanation is also supported by optimal foraging theory in hunter-gatherer tribes.) Further, the human gut morphology is not what might be expected for a strict vegetarian/fruit diet.

• Comparative physiology (metabolism)
  • Intestinal receptors for heme iron. The existence of intestinal receptors for the specific absorption of heme iron is strong evidence of adaptation to animal foods in the diet, as heme iron is found in nutritionally significant amounts only in animal foods (fauna).

  • B-12 an essential nutrient. Similarly, the requirement for vitamin B-12 in human nutrition, and the lack of reliable (year-round) plant sources suggests evolutionary adaptation to animal foods in the human diet.

  • Plant foods are poor sources of EFAs. In general, the EFAs in plant foods are in the "wrong" ratio (with the exception of a very few exotic, expensive oils), and the low synthesis rates of EPA, DHA, and other long-chain fatty acids from plant precursors point to plant foods as an "inferior" source of EFAs. This strongly suggests adaptation to foods that include preformed long-chain fatty acids, i.e., fauna.

  • Taurine synthesis rate. The low rate of taurine synthesis in humans, compared to that in herbivorous animals, suggests human adaptation to food sources of taurine (fauna) in the human diet.

  • Slow conversion of beta-carotene. The sluggish conversion rate of beta-carotene to vitamin A, especially when compared to the conversion rate in herbivorous animals, suggests adaptation to dietary sources of preformed vitamin A (i.e., a diet that includes fauna).

  • Plant foods available in evolution were poor zinc and iron sources. The plant foods available during evolution (fruits, vegetative plant parts, nuts, but no grains or legumes) generally provide low amounts of zinc and iron, two essential minerals. These minerals are provided by grains, but grains are products of agriculture (i.e., were not available during evolution), and contain many antinutrients that inhibit mineral absorption. This suggests that the nutritional requirements for iron and zinc were primarily met via animal foods during human evolution.

  • Bitter taste threshold as a trophic marker. An analysis of the human bitter taste threshold, when compared to the threshold of other mammals, suggests that our sensitivity to the bitter taste is comparable to that of carnivores/omnivores.

• There is no such thing as a veg*n gatherer tribe. And there are no records to indicate that any such tribes ever existed; also no evidence of any vegan societies either.

• The actual diets of all the great apes includes some fauna--animal foods. Even the great apes that are closest to being completely vegetarian, gorillas, deliberately consume insects when available. Chimps and bonobos, our closest relatives, hunt and kill vertebrates and eat occasional meat.

• Many of the ancillary claims made in comparative "proofs" of veg*n diets are logical fallacies:
  • The misinterpretation of animal studies using domesticated or feedlot meats to condemn all omnivore diets.

  • The misinterpretation of clinical studies showing negative results for the SAD/SWD as indicating negative results for all omnivore diets.

  • The misinterpretation of the results of the China Project to claim it "proves" vegan diets are best and all omnivore diets are bad.

Humans are classic examples of omnivores in all relevant anatomical traits. There is no basis in anatomy or physiology for the assumption that humans are pre-adapted to the vegetarian diet. For that reason, the best arguments in support of a meat-free diet remain ecological, ethical, and health concerns.

Note that grains, legumes, and/or dairy are generally not available to hunter-gatherers; such foods are provided in significant quantities only via agriculture, and have been a significant part of the human diet for only about 10,000 years or less. The extent of human genetic adaptation to such foods is a controversial point, but the majority view is that the genetic adaptation that has taken place in the last 10,000 years is quite limited. (See the discussions earlier herein regarding hereditary hemochromatosis, and the carnivore connection hypothesis.) Similarly, modern processed foods have been with us for only a few generations, and genetic adaptation in such a short period is highly unlikely.

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SEE TABLE OF CONTENTS FOR:
PART 1 PART 2 PART 3 PART 4 PART 5 PART 6 PART 7 PART 8 PART 9

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GO TO PART 1 - Brief Overview: What is the Relevance of Comparative Anatomical and Physiological "Proofs"?

GO TO PART 2 - Looking at Ape Diets: Myths, Realities, and Rationalizations

GO TO PART 3 - The Fossil-Record Evidence about Human Diet

GO TO PART 4 - Intelligence, Evolution of the Human Brain, and Diet

GO TO PART 5 - Limitations on Comparative Dietary Proofs

GO TO PART 6 - What Comparative Anatomy Does and Doesn't Tell Us about Human Diet

GO TO PART 7 - Insights about Human Nutrition & Digestion from Comparative Physiology

GO TO PART 8 - Further Issues in the Debate over Omnivorous vs. Vegetarian Diets

GO TO PART 9 - Conclusions: The End, or The Beginning of a New Approach to Your Diet?

Back to Research-Based Appraisals of Alternative Diet Lore