The omnivore vs herbivore debate is a common one, and while people can pick and choose particular elements to suit their point in an argument, the only way to properly address this is to lay out and analyse all of the anatomical evidence.
One of the most popular counter-arguments against veganism is that because humans have canine teeth and are able to eat animal flesh, we are therefore omnivores. An important fact that we must not forget is that while humans are capable of eating both plant and animal matter, of the two, we are able to thrive without eating animals—however, if we eat no plants, we die.
Our canine teeth are only that in name—human canine teeth are unlike the canine teeth of actual canines, which are really long and really pointed. Below is a collection of anatomical evidence which shows quite clearly what our features align with.
| FEATURE | CARNIVORE | OMNIVORE | HERBIVORE | HUMAN |
| Facial Muscles | Reduced to allow wide mouth gape | Reduced | Well-developed | Well-developed |
| Jaw Type | Angle not expanded | Angle not expanded | Expanded angle | Expanded angle |
| Jaw Joint Location | On same plane as molar teeth | On same plane as molar teeth | Above the plane of the molars | Above the plane of the molars |
| Jaw Motion | Shearing; minimal side-to-side motion | Shearing; minimal side-to-side motion | No shear; good side-to-side, front-to-back | No shear; good side-to-side, front-to-back |
| Major Jaw Muscles | Temporalis | Temporalis | Masseter and pterygoids | Masseter and pterygoids |
| Mouth Opening vs. Head Size | Large | Large | Small | Small |
| Teeth – Incisors | Short and pointed | Short and pointed | Broad, flattened and spade-shaped | Broad, flattened and spade-shaped |
| Teeth – Canines | Long, sharp and curved | Long, sharp and curved | Dull and short, or are long for defence, or none | Short and blunted |
| Teeth – Molars | Sharp, jagged and blade-shaped | Sharp blades and/or flattened | Flattened with cusps vs. complex surface | Flattened with nodular cusps |
| Chewing | None; swallows food whole | Swallows food whole and/or simple crushing | Extensive chewing necessary | Extensive chewing necessary |
| Saliva | No digestive enzymes | No digestive enzymes | Carbohydrate-digesting enzymes | Carbohydrate-digesting enzymes |
| Stomach Type | Simple | Simple | Simple or multiple chambers | Simple |
| Stomach Acidity (with food in stomach) | < pH 1 | < pH 1 | < pH 4-5 | < pH 4-5 |
| Length of Small Intestine | 3–6 times body length (push through raw flesh & animal protein quickly) |
4–6 times body length (push through raw flesh & animal protein quickly) |
10–12+ times body length | 10–11 times body length* |
| Colon | Simple, short, and smooth | Simple, short, and smooth | Long, complex; may be sacculated | Long, sacculated |
| Liver |
Can detoxify vitamin A | Can detoxify vitamin A | Cannot detoxify vitamin A | Cannot detoxify vitamin A |
| Kidney |
Extremely concentrated urine | Extremely concentrated urine | Moderately concentrated urine | Moderately concentrated urine |
| Nails | Sharp claws | Sharp claws | Flattened nails or blunt hooves | Flattened |
* “Body length” measured from neck to anus, as with the other animals.
Do Our Anatomical Features Align With the Omnivore or Herbivore?
A fair look at the evidence shows that humans are optimised for eating plant foods, according to the best evidence: our bodies. We’re most similar to other plant-eaters, and drastically different from carnivores and true omnivores. Those who insist that humans are omnivores, especially if their argument is based on canine teeth, would do well to look at what the evidence actually shows.
- The anatomical evidence tells us that we’re optimised for eating plant foods. The only way to come to another conclusion is to ignore the bulk of the anatomical evidence.
- Most plant-eaters eat small amounts of non-plant foods, usually insects (either intentionally or inadvertently). The small non-plant consumption of plant-eating animals doesn’t mean that they’re “omnivores” in the classical sense, and certainly doesn’t justify the idea that humans are adapted to a very mixed diet of plant and non-plant foods.
- “Omnivore” doesn’t mean 50% plants and 50% animals. Many of my critics consider chimpanzees to be omnivores but 95-99% of the chimp diet is plants, and most of the remainder isn’t meat, it’s termites. If humans are omnivores, then the anatomical evidence suggests that we’re the same kind: the kind that eats almost exclusively plant foods.
- The animals most similar to us, the other primates, eat an almost exclusively plant-based diet.
- Saying we’re omnivores because we’re capable of eating meat is just silly. We’re capable of eating cardboard, too. And by the “capable” argument, then cats are omnivores too, since nearly every commercial cat food has plant ingredients. Nobody would ever make the argument that cats are omnivores based on what they’re capable of eating, but they sure make that argument for humans, enthusiastically.
- Our so-called “canine teeth” are “canine” in name only. Other plant-eaters (like gorillas, horses, and hippos) have “canines”, and chimps, who are almost exclusively vegan, have massive canines compared to ours.
- Our early ancestors from at least four million years ago were almost exclusively vegetarian (source, article #5).
- Among animals, plant-eaters have the longest lifespans, and humans are certainly in that category (and yes, this was true even before modern medicine).
- We sleep about the same amount of time as other herbivores, and less than carnivores and true omnivores.
- The most common cause of choking deaths is eating meat (source). Real carnivores and omnivores don’t have that problem.
- The idea that a switch to meat-eating is what sparked early humans’ brain development has no more evidence to support it than the competing theories (such as that it was a switch to cooked foods that did the trick), and certainly doesn’t square with what comparative anatomy tells us.