Humans are biologically herbivores |
| Carnivores | Omnivores | Herbivores | Humans |
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 ptergoids | 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 long (for defense), 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 | 4-6 times body length | 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 nails |
From The Comparative Anatomy of Eating , by Milton R. Mills, M.D. |