Outline:Notes on the notion that humans are natural omnivores; we digest meat, have canine teeth, and have front-facing eyes

• Context
  • Those objecting to veganism often bring up one or more in a series of related complaints: that a vegan diet is not natural, that humans are omnivores and can digest meat, or that canine teeth and front-facing eyes are indications we are predators and not prey.
  • These protests are adequately dismissed with the first point below, which explains why they are not pertinent to the validity of veganism and therefore cannot diminish the case for veganism.
  • Although no further exploration of these claims is necessary once their lack of pertinence is demonstrated, we expound on these claims in case you're interested. It turns out that even if the objections were pertinent, they'd be nevertheless weak.
• The case for veganism does not depend on humans being natural herbivores or having specific physical traits.
  • Vegan diets are beyond sufficient for human health.
    • Even if humans were natural omnivores and our teeth and eye locations supported that assertion, the science is clear that a strictly herbivorous vegan diet is not only adequate but also beneficial to our health.
    • This is confirmed by Harvard Medical School, Mayo Clinic, Cleveland Clinic, Kaiser Permanente, NewYork-Presbyterian, the Academy of Nutrition and Dietetics operating in the United States, the Dietitians of Canada, the British Dietetic Association, the Dietitians Association of Australia, and others.
      • See http://justiceforanimals.org/objections/quote-we-need-animal-products-to-be-healthy/ for statements and citations.
    • These prominent organizations and others could only have made statements declaring the adequacy and salubriousness of a vegan diet if science supported such statements.
    • Cleveland Clinic even explicitly states, "There really are no disadvantages to a herbivorous diet!"
  • The case for veganism has nothing to do with this issue.
    • Simply put, the case for veganism is that it's ethically wrong to cause unnecessary harm to animals. Because it's not necessary to eat animal products for nutrition, any claims that we are natural herbivores are rendered meaningless.
• The evidence is strong that we lean toward being herbivorous.
  • Context
    • The fact that humans are behavioral omnivores and are able to get nutrition from both plants and animals says nothing about what is natural or optimum.
  • Our anatomy and physiology suggest that we are more herbivorous than omnivorous.
    • Context
      • A number of notable people have observed that anatomical and physiological traits of humans closely match herbivores'.
    • Dr. Mills's The Comparative Anatomy of Eating shows we more closely match herbivores in eighteen traits.
      • In all cases, humans more closely match herbivores.
      • A summary of Dr. Mills's traits comparison:
        • Intestines
          • Small intestine
            • Carnivore: 3–6 times body length
            • Omnivore: 4–6 times body length
            • Herbivore: 10–12+ times body length
            • Human: 10–11 times body length
          • Colon
            • Carnivore: Simple, short, and smooth
            • Omnivore: Simple, short, and smooth
            • Herbivore: Long, complex; may be sacculated
            • Human: Long, sacculated
        • Teeth
          • Incisors
            • Carnivore: Short and pointed
            • Omnivore: Short and pointed
            • Herbivore: Broad, flat, and spade shaped
            • Human: Broad, flat, and spade shaped
          • Canines
            • Carnivore: Long, sharp, and curved
            • Omnivore: Long, sharp, and curved
            • Herbivore: Dull and short or long (for defense) or none
            • Human: Short and blunted
          • Molars
            • Carnivore: Sharp, jagged, and blade shaped
            • Omnivore: Sharp blades or flattened
            • Herbivore: Flat with cusps vs. complex surface
            • Human: Flat with nodular cusps
        • Saliva
          • Carnivore: No digestive enzymes
          • Omnivore: No digestive enzymes
          • Herbivore: Carbohydrate-digesting enzymes
          • Human: Carbohydrate-digesting enzymes
        • Stomach
          • Stomach type
            • Carnivore: Simple
            • Omnivore: Simple
            • Herbivore: Simple or with multiple chambers
            • Human: Simple
          • Stomach acidity with food in stomach
            • Carnivore: ≤ pH 1
            • Omnivore: ≤ pH 1
            • Herbivore: pH 4–5
            • Human: pH 4–5
        • Chewing
          • Carnivore: None; swallows food whole
          • Omnivore: Swallows food whole or simple crushing
          • Herbivore: Extensive chewing necessary
          • Human: Extensive chewing necessary
        • Nails
          • Carnivore: Sharp claws
          • Omnivore: Sharp claws
          • Herbivore: Flat nails or blunt hooves
          • Human: Flat nails
        • Jaw
          • Type
            • Carnivore: Angle not expanded
            • Omnivore: Angle not expanded
            • Herbivore: Expanded angle
            • Human: Expanded angle
          • Joint location
            • Carnivore: On the same plane as molar teeth
            • Omnivore: On the same plane as molar teeth
            • Herbivore: Above the plane of the molars
            • Human: Above the plane of the molars
          • Motion
            • Carnivore: Shearing; minimal side-to-side motion
            • Omnivore: Shearing; minimal side-to-side motion
            • Herbivore: No shearing; good side-to-side, front-to-back motion
            • Human: No shearing; good side-to-side, front-to-back motion
          • Major muscles
            • Carnivore: Temporalis
            • Omnivore: Temporalis
            • Herbivore: Masseter and pterygoids
            • Human: Masseter and pterygoids
        • Mouth opening vs. head size
          • Carnivore: Large
          • Omnivore: Large
          • Herbivore: Small
          • Human: Small
        • Facial muscles
          • Carnivore: Reduced to allow wide mouth gape
          • Omnivore: Reduced
          • Herbivore: Well developed
          • Human: Well developed
        • Liver
          • Carnivore: Can detoxify vitamin A
          • Omnivore: Can detoxify vitamin A
          • Herbivore: Cannot detoxify vitamin A
          • Human: Cannot detoxify vitamin A
        • Kidney
          • Carnivore: Extremely concentrated urine
          • Omnivore: Extremely concentrated urine
          • Herbivore: Moderately concentrated urine
          • Human: Moderately concentrated urine
      • Source
      • Michael Bluejay summarized Mills's finding in a convenient chart.
    • Percy Bysshe Shelley wrote an entire book on the subject.
      • Shelley was a poet, not a scientist, but it's interesting to note that he wrote an entire book, A Vindication of Natural Diet, published in 1884, that drew on comparative anatomy to argue that humans were best suited to a vegetable diet.
        • Source
        • This predates Dr. Milton Mills's work, discussed above, by over 100 years.
  • Evolution and anthropology may support the contention that we are more herbivorous.
    • Biologist Rob Dunn declares in Scientific American that "human ancestors were nearly all vegetarians." In making that assertion, and in questioning the validity of paleo claims, he deems it important to look at the diets of our ancestors at the time our guts were evolving. He states that for primates, a group to which humans belong, plants "were our paleo diet for most of the last thirty million years during which our bodies, and our guts in particular, were evolving. In other words, there is very little evidence that our guts are terribly special and the job of a generalist primate gut is primarily to eat pieces of plants."
    • Dr. Colin Barras, a paleontologist and science writer, believes that "archaeologists tend to emphasise the role of meat in ancient human diets, largely because the butchered bones of wild animals are so likely to be preserved at dig sites. Edible plants may have been overlooked simply because their remains don’t survive so well."
  • Our inability to kill and eat animals and process meat without sophisticated tools is telling.
    • Omnivores and carnivores who eat animals have the athletic prowess and anatomical features necessary to not only catch and kill their prey but also to tear and rip apart the carcass and process it for eating.
    • Humans lack these features and must use sophisticated tools, such as spears and knives, to accomplish these tasks.
  • The adverse effects of eating animal products suggest that we are more herbivorous.
    • Supporting the contention that our evolution and physiology are herbivorous is the overwhelming scientific evidence that eating animal products contributes to all manner of health problems, including increased risk for obesity, high blood pressure, diabetes, heart disease, and cancer.
  • Extra
    • Widely reported but unverified quote:
      • The following quote will only be incorporated into the Article Tab and Clipboard Tab if an original source is found.
      • "Most of mankind for most of human history has lived on vegetarian or near-vegetarian diets.” —American Dietetic Association, now the Academy of Nutrition and Dietetics
• The notion of a natural diet is problematic.
  • The concept of a natural diet might make some sense in the context of gatherers and hunters. But since the invention of agriculture, with its selective breeding of both plant and animal species, the label loses its meaning.
  • To make the claim that humans are natural omnivores, one needs to define what is meant by "natural" in this context.
    • If by "natural" you are referring to the ability to obtain nutrients, then humans are omnivores, as we can digest both plants and meat. But, as shown earlier, that still cannot negate the case for veganism.
    • If you mean it's natural because it's nutritionally the best diet for humans, then you are on shaky ground. There's an increasingly large body of research, as mentioned and cited above, supporting the contention that the closer we are to a varied herbivorous diet, the greater our general health and the lower our risk for a multitude of chronic diseases.
  • The claim that humans are natural omnivores can be thought of as an example of the naturalistic fallacy. That is to say, being natural doesn't make something ethically or nutritionally sound.
• Canine teeth are not indicators of dietary requirements.
  • Context
    • As elaborated on earlier, the argument for veganism does not depend on humans having any specific physical traits.
  • Hippopotamuses, gorillas, camels, and saber-toothed deer all have sizable canines, and all are herbivorous.
  • Sizable canines in herbivores are often used as much for defense as for eating.
  • The relatively short, blunted canines in humans can assist in biting into hard, crunchy plants (such as apples) and ripping vegetable matter, preparing the food for grinding by the other teeth.
  • Our canines are not adequate to kill animals or tear raw flesh for eating.
• Front-facing eyes are not necessarily indicative of predator status.
  • Context
    • As elaborated on earlier, the argument for veganism does not depend on humans have any specific physical traits.
  • The claim is made that since many prey animals have eyes on the side of the head and many predator animals have eyes on the front of the head, it follows that humans, who have eyes on the front of the head, are designed to eat copious amounts of meat.
  • The point is made moot, however, not only by the fact that the argument for veganism does not depend on physical traits but also by the fact that our closest relatives in the animal kingdom, the primates, have eyes in the front of the head.
    • At least three advantages of frontal eyes for primates have been proposed:
      • Binocular vision is crucial for the manipulation of plant foods.
        • A study titled "Binocularity and brain evolution in primates," published by the National Academy of Sciences, concludes that "fine-grained stereopsis [binocular vision] is likely to be critical for the visually guided, delicate manipulation of plant foods."
      • The ability to "see through" foliage.
        • Theoretical neurobiologist Mark Changizi proposes in the Journal of Theoretical Biology the "X-ray vision" hypothesis. According to Changizi, front-facing eyes gave our ancestors the advantage of being able to "see through" the cluttered foliage in the forest. You can see this effect, he states, by placing a finger in front of your eyes and noting that the finger does not block the view of anything behind it.
      • Arboreal locomotion requires accurate depth and distance perception.
        • The depth and distance perception afforded by front-facing eyes was useful to our ancestors in jumping from branch to branch and tree to tree.
        • This idea was proposed in 1922 by Edward Collins and has subsequently been expanded and refined.
        • Source