Talk:In reply to: Humans are natural omnivores; we digest meat, have canine teeth, and have front-facing eyes

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
Meta
Context
Purpose
The purpose of this piece is to counter the objection to veganism that humans are natural omnivores because of our eating habits or other traits.
Contributors
Author: Greg Fuller Copy Editor: Isaac Nickerson
Revisions
2018-01-12 First published —glf
• 2018-01-24 Copy editor's first pass —isn