Evidence of Humans as Omnivores
Archeological Record
As far back as it can be traced, clearly the archeological record indicates an omnivorous diet for humans that included meat. Our ancestry is among the hunter/gatherers from the beginning. Once domestication of food sources began, it included both animals and plants.
Cell Types
Relative number and distribution of cell types, as well as structural specializations, are more important than overall length of the intestine to determining a typical diet. Dogs are typical carnivores, but their intestinal characteristics have more in common with omnivores. Wolves eat quite a lot of plant material.
Fermenting Vats
Nearly all plant eaters have fermenting vats (enlarged chambers where foods sits and microbes attack it). Ruminants like cattle and deer have forward sacs derived from remodeled esophagus and stomach. Horses, rhinos, and colobine monkeys have posterior, hindgut sacs. Humans have no such specializations.
Jaws
Although evidence on the structure and function of human hands and jaws, behavior, and evolutionary history also either support an omnivorous diet or fail to support strict vegetarianism, the best evidence comes from our teeth.
The short canines in humans are a functional consequence of the enlarged cranium and associated reduction of the size of the jaws. In primates, canines function as both defense weapons and visual threat devices. Interestingly, the primates with the largest canines (gorillas and gelada baboons) both have basically vegetarian diets. In archeological sites, broken human molars are most often confused with broken premolars and molars of pigs, a classic omnivore. On the other hand, some herbivores have well-developed incisors that are often mistaken for those of human teeth when found in archeological excavations.
Salivary Glands
These indicate we could be omnivores. Saliva and urine data vary, depending on diet, not taxonomic group.
Intestines
Intestinal absorption is a surface area, not linear problem. Dogs (which are carnivores) have intestinal specializations more characteristic of omnivores than carnivores such as cats. The relative number of crypts and cell types is a better indication of diet than simple length. We are intermediate between the two groups.
Conclusion
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.
[Dr. McArdle is a vegetarian and currently Scientific Advisor to The American Anti-Vivisection Society. He is an anatomist and a primatologist.]
