One of the most ridiculous and persistent false claims made by armchair nutritionists, meatarian propagandists, and even academics, who really should know better, is that the human species is an "omnivore"; that is, it should eat both plant and animal matter.
In general, this error is based on the accidental, or perhaps intentional, confusing of the verbs "to be" and "to do". If the human "is" a natural omnivore, then we should have ALL the physical and biochemical equipment that is NECESSARY to run down, kill with our bare hands, tear asunder, eat, and properly digest, RAW animal prey, just as ALL natural omnivores, or carnivores, do. Just looking at our bodies will conclusively prove that we do not have the claws or talons necessary to catch and hold animal prey, and we do not have the sharp, shearing teeth necessary to tear, not chew, animal flesh. We are not fast enough to outrun and catch animals. Natural omnivores or carnivores do NOT chew their eaten flesh, they tear it into chunks and swallow them whole. We do not have the "constant tendency for the last upper premolar and the first lower molar to engage and form long longitudinal opposed shearing blades (the carnassials)", which are a common characteristic of natural carnivores and omnivores.
No human cultural-carnivore kills its animal prey with his/her natural equipment, nor do they eat their animal prey raw. I have challenged countless meatarians to do so in the past 30 years, and NONE have shown the courage of their conceptual convictions and done so. Why? Simply because we are NOT an "omnivore". In fact, we have strong anti-killing instincts. Try to kill an animal with your bare hands to demonstrate this.
Any second-grader could differentiate between the verbs "be" and "do", yet this important distinction is totally ignored by cultural carnivores, and even academics with PhD's, who foolishly claim that because humans have been DOing cultural-carnivorism for a long time, that somehow (never explained) magically, we ARE "omnivores". They want to believe that DOing modifies BEing. They fail to understand the profound difference between Nature, and inviolable Natural Laws, and silly, self-destructive local cultural customs. By their absurd and faulty logic: because some humans DO murder, and because murder has existed throughout human history, ALL humans ARE born murderers.
http://ecologos.org/omni.htm