If humanity were fully adapted to eating and digesting nothing but meat, would the differencewith normal humans be visible from the outside?

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    $\begingroup$ That depends on what you mean specifically by "eating and digesting nothing but meat". Anatomically modern humans are adapted to eat and digest cooked food, with some small uncooked supplements consisting of particularly tender fruit, leaves and such. If you mean "adapted to eat uncooked food" (of any kind, vegetable, flesh, fish, doesn't matter) the anatomical differences would be pretty obvious. $\endgroup$
    – AlexP
    Jan 25, 2021 at 12:21
  • $\begingroup$ @AlexP, citation needed. I fail to see why a human with the GI system of, say, a pig, would be "pretty obvious". Maybe dentition, although now we need clarification of "visible from the outside". $\endgroup$
    – Matthew
    Jan 25, 2021 at 13:22
  • $\begingroup$ @Matthew: Our jaws are too small to eat uncooked food -- we simply don't have enough space for muscle attachment points, and the jaw bones are too gracile. Our teeth are also too small, and of the wrong shape. Look at our very close cousins the chipanzees to see how a human-like animal looks when adapted to eat raw food. $\endgroup$
    – AlexP
    Jan 25, 2021 at 13:26
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    $\begingroup$ we already have human populations that eat nothing but meat, native Mongolian and Inuit come to mind. $\endgroup$
    – John
    Jan 25, 2021 at 14:05
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    $\begingroup$ @user6760 Carnivorous-adapted humans should not have this problem as long as they eat organ meats (why wouldn't they?) and do not cook (like the Inuit). It is like saying a snake should have scurvy because it eats no vegetables. But humans, especially in the Western World, tend to only eat muscle and we cook it. They could also possibly regain their ability to produce their own Vitamin C. $\endgroup$
    – DKNguyen
    Jan 25, 2021 at 14:37

3 Answers 3


Likely Not (on some broad assumptions):

Given that humans can adapt their environments around them to their needs, it is quite possible that humans (if they TODAY became obligate carnivores) wouldn't look significantly different. After all, they got there with the equipment they have - tiny mouths and no fangs or claws. Humans don't NEED those things to kill everything in their environment.

I'm not sure what conditions you want to impose to make people carnivores. As John pointed out, there are populations that do this already, and few carnivores are utterly and exclusively carnivore. It's more a line drawn by people, and has a lot more subtlety.

But a human with a gun/bow, a knife, and fire is more than capable of switching to a carnivorous diet. They don't need to look like predators to do so. Most of the meat humans eat today isn't hunted anyway. If you were trying to adapt a herbivore to carnivore behavior, it might be different. But humans already have adaptations to be predators, most critically in our body plan (efficient endurance predator) and our eyes (forward facing/excellent stereoscopic sight).

It's also entirely possible that going forward, carnivore humans might have evolutionary pressures that would shift them in a different direction for digestion (not usually obvious from outside) dentition (whatever is most efficient for chewing cooked meat) or pupil shape (if we become nocturnal or ambush predators). If we stopped being endurance predators, our body shape might shift as well. We might see people undergoing speciation as different hunting niches are filled by humans. Not being gatherers might have (in the long run) unforeseen consequences on what we looked like.

But given a start of modern humans with a small shift to make us obligate carnivores, I think humans would be perfectly adapted. Most of our meat would NOT come from hunting, but animal husbandry. We would continue to gather food for cows, goats, chickens and sheep. There would be a larger emphasis on what parts of animals we ate (to give the best nutrition) but otherwise more meat would just displace the "and potatoes" part of the dinner table. DKNguyen wisely pointed out there are some vitamins damaged by cooking, and our carnivores would likely need to use various compensations to deal with that (fermentation, chemical marinating like with lemon juice/lye [think lutefisk] and supplements) but even cats may potentially eat grass as a source of folic acid, so your carni-humans might season food with plants containing trace nutrients.

  • $\begingroup$ As well as reduced cooking since cooking destroys a lot of the components that are in meat (especially organ meats) that we would otherwise have to eat FRESH fruits and vegetables for. $\endgroup$
    – DKNguyen
    Jan 25, 2021 at 14:35
  • $\begingroup$ @DKNguyen true, although the internal organs tend to be less tough and are probably easier to eat raw than muscle. Never tried raw liver; never personally cared for sweetmeats either. Maybe marinating/pickling? $\endgroup$
    – DWKraus
    Jan 25, 2021 at 14:39
  • $\begingroup$ You know, pickiling never occurred to me but sailors had scurvy from preserved foods so I assume it may have the same effect. Whatever the case, time likely has the same degrading effect no matter what you do. A big reason why we must cook is that we do not eat our food fresh from the kill; We essentially eat a bacteria-ridden corpse killed elsewhere some time ago. That raises a potential farming issue for large populations in an urban environment. $\endgroup$
    – DKNguyen
    Jan 25, 2021 at 14:40
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    $\begingroup$ @DKNguyen The German Navy got vitamin C from fermenting cabbage (sauerkraut) so bacterial activity could be an important nutritional supplement. Some people will hang meat (basically letting it rot for a while) to make it "tender." Sound gross to me, but hey. $\endgroup$
    – DWKraus
    Jan 25, 2021 at 14:43
  • $\begingroup$ I'm going to have to read up on what preservation methods do and do not destroy Vitamin C. Did European sailors just not know to preserve fruits and vegetables? Seems unlikely. Or just super adverse to preserved organ meats? $\endgroup$
    – DKNguyen
    Jan 25, 2021 at 14:45

Tigers, leopard seals and wolves are carnivore.

Let's compare their "smiling devices" with those of a human.

For a tiger this is what they look like

Tiger fangs

These are those of a leopard seal

leopard seal fangs

These are those of a wolf

wolf fangs

And these are those of a human

human teeth

I guess the differences are pretty obvious:

  • bigger canines and incisive
  • teeth intended to cut and lacerate, not to smash
  • jaw intended to have a broader opening to better bite the prey
  • $\begingroup$ Let's also add in that the mouth would likely also have less side-to-side mobility than it does for us and smaller cheeks, as a carnivorous diet usually requires a less flexible jaw more focused on opening and closing movement and on a wider gape $\endgroup$ Jan 25, 2021 at 13:47
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    $\begingroup$ These jaw changes would be required to change Humans into Predators, not to change them into Carnivores. Those jaws are designed to eat raw meat from prey... And to hunt and kill the prey in the first place. OP does not specify hunter. OP does not even specify uncooked. $\endgroup$
    – PcMan
    Jan 25, 2021 at 14:05
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    $\begingroup$ Do notice though that our closest relatives, chimps, have some really big mouths and canine teeth and they are omnivores just like us. Our teeth evolved to be "cuter" because we didn't need to masticate so much after mastering fire and tools. $\endgroup$ Jan 25, 2021 at 15:07

There has been a (mainly) carnivore sub-species, named Neanderthal. While I still learned in school that their physical appearance was because of their meat-only diet, nowadays it is known that neither they only fed on meat, nor was their appearance completely influenced by it. Depending on the scenario, you still can pick some interesting parts. We believed the original "historical facts" for that long probably only because it sounded cool.

You can find some pictures on Google to look at. Below is an example. They had a bit stronger appearance and were larger (for their time).

Neanderthal - reconstruction by Adam Sacco, original source gone