Herbivore | Omnivore | Carnivore
This made me think of humanities place within this potential contrast.
For example a Panda bear exclusively eats bamboo (Herbivore) and a Polar Bear exclusively eats Meat - they can probably eat some vegetables (saw them eating carrots in a zoo) as well but their natural diet is almost all meat. A Panda could also probably eat some meat but the idea is they are definitely more one or the other. Another dividing factors isn't just "will eat meat" but will actually hunt or kill an animal to get it. There are a lot of animals that could or would eat meat if it was in front of them but wouldn't ever kill for it. Dears - pigs - cows are examples. There are cases where people have seen dear eating dead animals but dears don't and wouldn't hunt for it.
With birds a parrot is exclusively a seed/ fruit/ vegetable eater where as Eagles only eat meat.
Most lizards are carnivores but Iguanas and some others are exclusive herbivores.
You can notice the refinement of the features in the carnivore in this example. They can swim a lot faster - are a lot smarter - and have additional senses like echo-location. Dolphins are an interesting example because while they eat fish - the fish themselves are more like plants in a way. An Orca (Large dolphin) is probably a better example because they will eat sharks, other mammals - seals and even other dolphins or whales. There is a difference between eating a seal and some small fish - both physically and mentally and especially behaviorally.
I think like a lot of things it comes down to Location. If humans are in the Arctic - like the polar bears - there are not any plants to eat so to live there you have to eat other animals - so they become almost exclusive hunters. As you move more south and there are more plants - we become more omnivorous. When we get to places that are an abundant supply of plants to eat - we become even more herbivores - sometimes - like the gorilla - exclusively so.
I'm thinking that maybe it was the humans that migrated north - and had to survive an ice age that developed into becoming almost exclusive carnivores - aka hunters - and it was from them that we inherited a lot of different characteristics, behaviors, and especially technologies. If you imagine the difference between a dolphin and a manatee - you can also imagine the difference between a gorilla and a social hunter. Like a wolf pack - we developed co-operative communication to take down large prey - because in the super cold places we needed large prey - larger than us - to sustain us. That requires co-op hunting eg. One lion can't do much but a pride can take down almost anything.
So humans became the "Apex" predator - similar to an Elephant becoming the Apex herbivore - who's size kept them out of reach from almost all predators - it was our brains that grew in response to predatory requirements for survival. In the far North (and south) there are not any other options.
I think another interesting aspect to this is that different groups of humans would evolve to suite their diets creating types of humans that broached both sides of the carnivore/ herbivore divide. To be able to migrate away from fugitive areas requires the ability to hunt or fish - because it's almost impossible to travel and carry enough vegetable food to sustain the trip - especially when you don't know where you are going or what is there to eat. What this means is that it was carnivore-inclined humans that spread throughout the world leaving behind their propensities and predatory refined genetics to areas that could enable - especially with agriculture - vegetarian diets.
Given the option a plant based diet is superior as most cancer and disease is caused by diet - especially from catching these from the meat we eat and the keeping of the animals used. Not only that but the idea that meat has a higher calorie to amount eaten ratio is quickly ruined by the amount of food required to feed the animals to be slaughtered.
If you had an apple tree that provided enough food for your entire family - to live perpetually healthily and peacefully. Would you cut it down to make spears and firewood to kill and eat some animals - who would then run away or go extinct - being left without an apple tree or anything else to eat? Forbidden fruit and the knowledge of "good and evil" could easily be an analogy of this.
The evidence of cannibalism and the interactions between neanderthals and early humans also show the behavior of carnivores.
In a world where the only advantage of eating meat, to our health and the environment - not to mention the morality of it - is the "taste" -is selfish - dogmatic - and retarded.
That being said It would be pretty cool to see, (not in person) a carnivore horse or elephant.