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  • Writer's pictureMeg

But from an Evolutionary Perspective, Aren’t we Omnivores?

Updated: May 31, 2022

“Non-violence leads to the highest ethics, which is the goal of all evolution. Until we stop harming all other living beings, we are still savages.” Thomas A. Edison
2016-03-26 22.33.19

In my experience, the idea that humans are supposed to eat meat is one of the most pervasive justifications for continuing to eat animals, to the detriment of our health and the planet. I read one of the most enlightening articles of my life earlier this year entitled Four Ways People Rationalise Eating Meat. In it Melanie Joy, an incredible Psychologist, Sociologist and author explains how she coined the Three N’s of Justification (3Ns). She proposes that, culturally we tell ourselves that eating meat is: naturalnormal, and necessary.

“Joy argues that through a recurrent process of socialisation people come to believe that eating meat is natural – that eating meat is written in our biology, meat is what we naturally crave, and it is what our species evolved to eat; that eating meat is normal – that it is what most people in civilized society do and what most people expect from us; and that eating meat is necessary – that we need meat for survival or that we need to consume at least some meat to be strong, fully healthy individuals. Joy proposes that the 3Ns are widespread beliefs that are reinforced through various social channels, including family, media, religion, and various private and public organisations. For example, one popular belief related to the necessity of eating meat is the idea that one cannot maintain a diet that contains enough protein without consuming at least some meat. Although scientists, including the American Dietetic Association (ADA), America’s leading organisation of nutritionists, have released numerous publications showing that this is not the case” – SBS News

To test the 3Ns theory, Jared Piazza, a Psychologist at Lancaster University, conducted a study in which two samples of survey respondents (176 UPenn undergrads in the first, 107 American Mechanical Turk workers) were asked in an open-ended way why it’s okay to eat meat. For the study, they added a fourth N, Nicethat eating meat is justified because it tastes nice.

The results, with the first survey (undergrads) on the left and the second on the right (mechanics):


As you can see, in both samples “necessary” — that is, the belief that we need meat for survival or that we need to consume at least some meat to be strong, fully healthy individuals (which is the easiest to disprove empirically) — was the most commonly cited justification for eating meat.

So now we know this bias exists both anecdotally and empirically. This belief manifests itself in so many interactions I've have with non-vegans:

"Why weren’t cave men vegans then?"

"We’re omnivores/carnivores"

"We need meat to survive/thrive/function optimally"

"Well then why do we have that one pointy tooth?"

"You’re pale because you’re vegan"

"Vegans don’t get enough protein/iron"

The idea that humans are omnivores is obviously a deep-seated belief, with extraordinary evidence to the contrary (and people who think humans are carnivores need to revise biology). In previous blogs I’ve discussed at length the health detriment of meat and dairy consumption and the heath benefits of plant-based eating.

Though behaviourally humans are omnivores, anatomically and physiologically they are not, as explained by the following classifications of characteristics offered by William Roberts (MD) and others:

  • Appendages – Carnivores have claws, herbivores have hands and hooves

  • Teeth – Human canines (sometimes referred to as our ‘pointy or ‘streak tooth’…) are blunt, small and not serrated, whereas carnivores are elongated and serrated for killing prey. Human molars are squared and flattened for grinding and crushing, whereas carnivores are sharp.

  • Similarly, oral cavity compared to head size – Carnivores oral cavity is large and wide, with hinge joint jaws and limited side to side motion, whereas herbivores oral cavity is small with a jaw joint above the level of the teeth and a complex range of motion. Herbivores jaws are less stable and strong than that of carnivores. Image trying to bite the rump of a living cow…

  • Intestinal Tract – Carnivores are short, at 3 times the length of body whereas herbivores are long at 12 times the length of body. Human’s intestinal tract is about 10 times the length of their body, which permits the digestion of fibres in plant matter.

  • Digestion – Herbivores chew to disrupt plant cell walls and our saliva contains digestive enzymes, carnivores have no such enzymes.

  • Stomach – A herbivores stomach is about 25% of gastrointestinal tract volume requiring small frequent meals, whereas a carnivores stomach has twice that capacity, about 60-70% of gastrointestinal tract volume, which require large less frequent meals.

  • Stomach Ph – Herbivores have less acidic stomachs with a Ph of about 4-5 with food, whereas carnivores secrete more hydrochloric acid and have an overall more acidic stomach with a ph of about 1 or less with food. Carnivore’s acidic stomach is advantageous to kill bacteria in decaying flesh.

  • Body cooling – Carnivores by panting, herbivores by sweating.

  • Drink fluid – Carnivores by lapping, herbivores by sipping.

  • Vitamin C – Carnivores produce their own, whereas herbivores obtain it through their diet. Humans contract scurvy if they do not obtain vitamin C through eating fruits and vegetables.

  • Artherosclerosis – Affects only herbivores. Dogs, cats and lions can be saturated with fat and cholesterol and atherosclerotic plaques do not develop. Hence, if humans were omnivores heart disease would not exist. As we’re not, it’s the number one preventable disease killing around 1 in every 4 of us.

Therefore, humans have characteristics of herbivores, not carnivores or omnivores. Our closest relative, the chimpanzee is physiologically and anatomically a herbivore, although on occasion enjoys a free-range, grass fed monkey (assumes 2-3% of their diet). It would appear, like us, they are herbivores but behaviourally omnivores (at times).

Thanks for reading,

Meg x

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