No human canines are small compared to the canines. That's a very incorrect argument. The other way is.. if we are meant to be carnivorous we would have huge canines, instead we have well developed molar to chew like bovines. Also our intestines are long whereas carnivores have small intestines to throw out meat quickly before they rot. So that argument given by mullahs is not very scientific. This just proves that evolution is an ongoing process.
Let's not look at us vs them. Religion is a problem when you are talking about culture. If you put a health tax on meat eaters as they would ultimately eat up healthcare resources, like we have a sugar or fat tax, it is secular and will push people to eat healthy irrespective of rwligion.
Yeah. All arguments of Humans being natural meat eaters have been debunked.
Humans are naturally plant-eaters
according to the best evidence: our bodies
by Michael Bluejay • June 2002 • Updated December 2015
A fair look at the evidence shows that humans are optimized for eating mostly or exclusively plant foods, according to the best evidence: our bodies. We're most similar to other plant-eaters, and drastically different from carnivores and true omnivores.1,2,3
Those who insist that humans are omnivores, especially if their argument is based on canine teeth, would do well to look at what the evidence actually shows. We'll cover that below.
I first wrote this article many years ago, but since then Milton Mills, M.D. published
an excellent paper which covers the anatomy of eating, so let's skip right to my table-ized summary of his research:
Humans are biologically herbivorous
Carnivores
Omnivores
Herbivores
Humans
Facial muscles
Reduced to allow wide mouth gape
Reduced
Well-developed
Well-developed
Jaw type
Angle not expanded
Angle not expanded
Expanded angle
Expanded angle
Jaw joint location
On same plane as molar teeth
On same plane as molar teeth
Above the plane of the molars
Above the plane of the molars
Jaw motion
Shearing; minimal side-to-side motion
Shearing; minimal side-to-side motion No shear; good side-to-side, front-to-back
No shear; good side-to-side, front-to-back
Major jaw muscles
Temporalis
Temporalis
Masseter and ptergoids
Masseter and pterygoids
Mouth opening vs. head size
Large
Large
Small
Small
Teeth: Incisors
Short and pointed
Short and pointed
Broad, flattened and spade-shaped
Broad, flattened and spade-shaped
Teeth: Canines
Long, sharp, and curved
Long, sharp and curved
Dull and short or long (for defense), or none
Short and blunted
Teeth: Molars
Sharp, jagged and blade-shaped
Sharp blades and/or flattened
Flattened with cusps vs. complex surface
Flattened with nodular cusps
Chewing
None; swallows food whole
Swallows food whole and/or simple crushing
Extensive chewing necessary
Extensive chewing necessary
Saliva
No digestive enzymes
No digestive enzymes
Carbohydrate digesting enzymes
Carbohydrate digesting enzymes
Stomach type
Simple
Simple
Simple or multiple chambers
Simple
Stomach acidity with food in stomach
≤ pH 1
≤ pH 1
pH 4-5
pH 4-5
Length of small intestine
3-6 times body length
4-6 times body length
10-12+ times body length
10-11 times body length*
Colon
Simple, short, and smooth
Simple, short, and smooth
Long, complex; may be sacculated
Long, sacculated
Liver
Can detoxify vitamin A
Can detoxify vitamin A
Cannot detoxify vitamin A
Cannot detoxify vitamin A
Kidney
Extremely concentrated urine
Extremely concentrated urine
Moderately concentrated urine
Moderately concentrated urine
Nails
Sharp claws
Sharp claws
Flattened nails or blunt hooves
Flattened nails
From
The Comparative Anatomy of Eating, by Milton R. Mills, M.D. | "Body length" measured from neck to anus, as with the other animals
The details are in Mills' paper. The rest of this article covers mostly angles not in that paper.
Summary of this article
- The anatomical evidence tells us that we're optimized for eating mostly or exclusively plant foods. The only way to come to another conclusion is to ignore the bulk of the anatomical evidence. (Critics of this article either use inferior evidence, such as disputed assumptions about the prehistoric diet, or they cherry-pick the anatomical evidence while ignoring the bulk of it.)
- Most plant-eaters eat small amounts of non-plant foods, usually insects (either intentionally or inadvertently). The small non-plant consumption of plant-eating animals doesn't mean that they're "omnivores" in the classical sense, and certainly doesn't justify the idea that humans are adapted to a very mixed diet of plant and non-plant foods.
- "Omnivore" doesn't mean 50% plants and 50% animals. Many of my critics consider chimpanzees to be omnivores but 95-99% of the chimp diet is plants, and most of the remainder isn't meat, it's termites. (see below) If humans are omnivores, then the anatomical evidence suggests that we're the same kind: the kind that eats almost exclusively plant foods.
Chimpanzee: Pretty amazing canines for an animal that's as much as 99% vegetarian (and whose main non-veg food isn't meat, it's termites). (Source:
Creative Commons)
- The animals most similar to us, the other primates, eat an almost exclusively vegan diet.
- Saying we're omnivores because we're capable of eating meat is just silly. We're capable of eating cardboard, too. And by the "capable" argument, then cats are omnivores too, since nearly every commercial cat food has plant ingredients. (Check the label.) Nobody would ever make the argument that cats are omnivores based on what they're capable of eating. But they sure make that argument for humans, enthusiastically.
- Our so-called "canine teeth" are "canine" in name only. Other plant-eaters (like gorillas, horses, and hippos) have "canines", and chimps, who are almost exclusively vegan, have massive canines compared to ours.
- Our early ancestors from at least four million years ago were almost exclusively vegetarian.(source, article #5)
- Among animals, plant-eaters have the longest lifespans, and humans are certainly in that category (and yes, this was true even before modern medicine).
- We sleep about the same amount of time as other herbivores, and less than carnivores and true omnivores.
- The most common cause of choking deaths is eating meat. (source) Real carnivores and omnivores don't have that problem.
- The idea that a switch to meat-eating is what sparked early humans' brain development has no more evidence to support it than the competing theories (such as that it was a switch to cooked foods that did the trick), and certainly doesn't square with what comparative anatomy tells us.
Looking at the evidence fairly
The meat-eating reader already has half a dozen objections to this before s/he's even read the rest of the article, and I will address those objections specifically, but first let me address them generally: It's human nature to want to feel that what we're doing is right, proper, and logical. When we're confronted with something that suggests that our long-held belief might actually be wrong, it's uncomfortable. We can either consider the new evidence fairly, adding to the discomfort about our possible error, or we can reject that premise without truly considering it, which allows us to sidestep any uncomfortable feelings. And we do this by searching our minds for any possible arguments for why the challenge must be wrong, to justify our current beliefs. This practice is so common psychologists have a name for it:
cognitive dissonance.
While we prefer to believe we act on reason, a formidable amount of psychological research shows the opposite: Often to usually, our actions aren't based on our arguments. Rather, our actions
come first and
then we come up with the arguments to try to support those actions. If we were truly logical, we'd consider the evidence
first and
then decide the best course of action. But often we have it in reverse, because it's too difficult to accept that we might have been wrong.
Vegan bodybuilders shatter the myth that vegans are skinny and malnourished.
(Pictured: Avi Lehyani, anonymous, Ryan Wilson, Robert Cheeke)
This is particularly true when it comes to vegetarianism. It's easy to identify because the anti-vegetarian arguments are usually so extreme, compared to other kinds of discourse. A person who would never normally suggest something so fantastic as the idea that plants can think and feel pain, will suddenly all but lunge for such an argument if they feel a need to justify their meat-eating. That's psychology for you.
So I challenge you: stop trying to figure out ways that I "must" be wrong even before you've bothered to read the rest of this article. Instead, read it, and actually
consider it rather than reflexively trying to come out with ways to dismiss it out of hand. You can certainly still disagree after you've considered all the evidence—but not
before. (Most of my critics miss that point, emailing me arguments that are already rebutted here in the article, which they didn't bother to actually read.)
Many readers will find it necessary to try to defeat me, at least in their minds, so let's agree that that would mean providing
more and
better evidence for your position. One does not win the argument by making a single point, as most who've written to me seem to think. The evidence favoring a plant-based diet for humans is clear, convincing, and
overwhelming. There is definitely some evidence for the other side, to be sure, but it's simply not nearly as strong. While that ought to be obvious, I mention it because my critics seem to believe that all the evidence I present somehow
vanishes into thin air when they present their one lone argument. As though making a single point and ignoring all other evidence to the contrary wins the day.
In graphical form, it goes like this:
Evidence that humans' anatomy favors a plant-based diet
Evidence to the contrary
Lunging at the minority of evidence in the red box doesn't make the contrary position more compelling. The only way to make the contrary position compelling is to present more and better evidence (making the red box bigger), not to pretend that the green box doesn't exist.
The most common counter-arguments
Chimpanzee: Pretty amazing canines for an animal that's as much as 99% vegetarian (and whose main non-veg food isn't meat, it's termites). (Source:
Creative Commons)
"Humans have canine teeth. End of story."
The truth is our so-called "canine teeth" are canine in
name only. Humans' "canine teeth" are unlike the canine teeth of
actual canines, which are
really long and really pointed. Our teeth are absolutely not like theirs. In fact, other vegetarian animals (like
gorillas,
horses, and
hippos) possess the same so-called "canine" teeth, which are often used for
defensive purposes rather than for eating. Check out the chimpanzee picture at right, and consider that chimps' diets are up to 99% vegetarian (and what little non-vegetarian food they eat usually isn't meat, it's termites). And remember that we're more similar to chimps than to any other animal.
John A. McDougall, M.D., has
a good take on this:
Our dentition evolved for processing starches, fruits, and vegetables, not tearing and masticating flesh. Our oft-cited "canine" teeth are not at all comparable to the sharp teeth of true carnivores. I lecture to over 10,000 dentists, dental hygienists, and oral specialists every year, and I always ask them to show me the “canine” teeth in a person’s mouth – those that resemble a cat’s or dog’s teeth – I am still waiting to be shown the first example of a sharply pointed canine tooth.
If you have any doubt of the truth of this observation then go look in the mirror right now – you may have learned to call your 4 corner front teeth, “canine teeth” – but in no way do they resemble the sharp, jagged, blades of a true carnivore – your corner teeth are short, blunted, and flat on top (or slightly rounded at most). Nor do they ever function in the manner of true canine teeth. Have you ever observed someone purposely favoring these teeth while tearing off a piece of steak or chewing it? Nor have I. The lower jaw of a meat-eating animal has very little side-to-side motion – it is fixed to open and close, which adds strength and stability to its powerful bite. Like other plant-eating animals our jaw can move forwards and backwards, and side-to-side, as well as open and close, for biting off pieces of plant matter, and then grinding them into smaller pieces with our flat molars.
The canine argument is important for what it reveals: The people who make it place
so much importance on it, insisting that humans having canines immediately wins the whole argument, all by itself, case closed! But when they discover that they were wrong, then suddenly the canine issue really
wasn't so important to them after all, and they simply move on to their next misconception, as though their previous argument never happened. That really lays their motivations bare: They were never really interested in evaluating the evidence, they were only interested in being right. But really, if someone thinks that canine teeth are the be-all and end-all of the herbivore vs. omnivore debate, then when they find out that they're wrong about teeth,
that ought to tell them something. But does it ever? Nope. If we needed evidence of bias, there you have it.
"Humans have always eaten meat."
No, we haven't, and I'll provide evidence for that shortly. More importantly, early humans, like modern humans, could have simply acted outside of instinct, and made interesting dietary choices contrary to their anatomy. We really have to look at
our anatomy to get the best evidence for what we're optimized for eating, not what some humans
chose to eat. Otherwise, thousands of years from now anthropologists might conclude that eating McDonald's is natural because humans in the 20th and 21st centuries used to eat a lot of it.
Also, of early humans who did eat meat, they might have eaten it as sparingly as modern chimps do.
"We're capable of eating meat, therefore we're omnivores. Case closed."
Okay, fine, then cats are omnivores, too. ("Case closed.") Commercial cat foods, both wet and dry, contain things like
rice, corn, and wheat. In fact, some people feed their cats
a pure vegan diet with no meat at all.
But of course, cats are true carnivores. We don't call them omnivores just because they'll eat things contrary to what nature intended. That would be silly. No one makes that argument for cats. But they make it for humans, enthusiastically. However, they can't have it both ways: Either we
don't assume humans are omnivores just because we can eat meat, or we apply the same standard to other animals and conclude that cats are omnivores, too. Which is it?
"Humans are omnivores."
"Omnivore" doesn't mean 50% plants and 50% animals. Many consider chimpanzees to be omnivores but 95-99% of their diet is plants, and most of the rest isn't meat, it's termites. If humans are omnivores, then the anatomical evidence suggests that we're the same kind: the kind that eats almost exclusively plant foods. And if an omnivore is an animal that is
capable of eating both plants and animals, and
ever does so, then sure, we're omnivores, but then again, so are cats. (See above.) A
true omnivore would have a body
optimized for eating both plants and animals. With non-humans we can look at what they eat in the wild to figure out their preferred diets, but humans lost our instincts long ago, so we can look only at our anatomy and digestive systems. And
that evidence is compelling.
"You're not a credible source."
You don't have to believe me, you can look at the evidence I cite. My critics talk as though I claim this article to be original research, but really, I'm just reporting on what the science says, citing credible sources along the way.
It's funny, my critics think I'm not allowed to speak without credentials, but somehow they don't need any themselves in order to argue the contrary position. For example, when Internet forums discuss whether meat-eating is natural, someone will undoubtedly lunge at the "canines = meat-eater" argument, then someone else will point them to this article where I explain that other plant-eaters have larger canines than ours, then the canine guy will exclaim, "Bluejay isn't a credible source! He has no formal training!" As though the critic has a Ph.D. in biology. And as though my own lack of credentials means than gorillas, horses, and hippos
don't have large canine teeth. The critics don't think they need any special training to spout off (wrong) pronouncements about human canines, for example, but anyone who dares disagree with their misinformed assumptions had better have multiple advanced degrees and tenure at an Ivy League university.
What matters is the evidence, and I cite my sources. If the critics have better evidence, rather than pulling pronouncements about canine teeth out of the ether, they'd do well to present it, rather than just dismiss evidence they don't like out of hand.
By the way, doctors like
John McDougall and
Milton R. Mills (both M.D.'s) believe that human anatomy favors plant foods. I wonder whether the people who send me hate mail about this article and tell me I'm an idiot would feel just as confident in telling these two doctors that the doctors are idiots, too?
"Vitamin B12. End of story."
I'm not joking when I tack on "End of story" to the sample counter-arguments. People actually make them that way, literally. Here again, they think one point invalidates all other evidence. Amazing.
The argument here is that since B12 isn't found in plant foods and modern vegans must supplement, a vegan diet can't be natural. Here's what's wrong with that argument:
- B12 isn't made by animals, it's made by bacteria. (source) It's found in animal foods because they're a hotbed of bacterial activity. It's also found in feces of most species. Historically it was easier for vegans to get B12 because their environment was so dirty. Plants pulled from the ground and not washed scrupulously could have bacterial contamination, and thus B12. (source)
- B12 is also found in lakes, before the water is sanitized. (source)
- Remember that "plant-eaters" aren't exclusively plant-eaters; they eat some small amounts of non-plant foods. For example, of the 1-5% of chimps' diets that aren't plants, most is generally termites, which happen to be loaded with B12. (source)
- We saw that fecal matter contaminating the environment can provide B12. But not taking any chances, many plant-eating animals actually eat their own feces. Prehistoric humans might have done the same. (Human feces is loaded with B12.) (source)
- Because the ability to absorb B12 decreases with age, the Food and Nutrition board says that all people over 50 should eat B12-fortified food or take B12 supplements, not just vegans. (source)
So the idea that our bodies are designed to eat large amounts of meat because of a single vitamin made by bacteria isn't very compelling.
In any event, there's no question that modern vegans must take a B12 supplement, recommended at least weekly. (
source) No plant food is a reliable source, and most fermented products (like tempeh) which list B12 on the Nutrition Facts actually don't have any, because the FDA mandates the wrong test for B12. (
source)
"Other primates eat meat."
Hardly. Various sources (below) say that a chimp's diet is 95-99% plant foods, and the primary non-plant food isn't meat, it's termites. Remember also that primates are intelligent and can make choices outside of instinct, just like humans do, so the tiny amount of meat they might eat could be due to choice, not instinct.
I cover the primate diet in more detail below.
"You're not considering evolution."
How so? However much our species has changed, the end result is that our anatomy still favors a predominantly plant diet.
But haven't humans always eaten a lot of meat?
In a word, no, which we'll discuss in a moment, but first there's something more important: Best evidence is
our anatomy, not what our ancestors ate in the recent or distant past
. Humans act by idea rather than by instinct, so we certainly can and do make choices that go against what's most "natural". Most other animals are programmed to know what their ideal food is. We are not. For us, it's learned behavior. Or in some cases, guessed behavior. We can make choices about what we should eat even if that's contrary to good health, as millions prove every day when they eat at McDonald's. If our ancestors ate meat, they were simply being human and making choices rather than acting on instinct. Think about it: Do you really believe that cavemen were true experts about nutrition? If so, what other major decisions about your life would you like to put in the hands of a caveman?
And in fact, even other primates learn their eating behavior from others:
Just as human travelers often adopt the local cuisine, wild monkeys learn to eat what those around them are eating, new research finds. A study of wild vervet monkeys (Chlorocebus aethiops) in South Africa provides proof that primates other than humans adopt and conform to cultural behaviors. Given a choice between two foods, infant monkeys ate only the foods that their mothers ate. And young males that ventured to other groups soon switched to the local diet, researchers report online today (April 25) in the journal Science. "Some of the ways of learning that we have thought were distinctly human are more broadly shared across nonhuman primates," said study co-author Andrew Whiten, a cognitive biologist at the University of St. Andrews in the United Kingdom. (
Live Science, April 2013)
So the best evidence isn't historical diets, best evidence is our own bodies. If we'd really been eating a lot of meat for a long time, that would be reflected in our anatomy, but it's not. Anyway, let's return to the assumption that our ancestors did eat a lot of meat. I can't think of a better example of a case in which people believe something to be true just because they assume it is. We all grew up thinking that our predecessors were huge meat-eaters, but where did we get that idea? Is it true just because it's part of our collective consciousness? More importantly, what does the evidence say?
John A. McDougall, M.D., perhaps the most knowledgeable expert on the relationship between diet and disease, asserts that our early ancestors from at least four million years ago followed diets almost exclusively of plant foods. (
source, article #5) Many other scientists believe that early humans were largely vegetarian. For example, biologist Robert Dunn, writing in Scientific American, says:
The majority of the food consumed by primates today–and every indication is for the last thirty million years–is vegetable, not animal. Plants are what our apey and even earlier ancestors ate; they were our paleo diet for most of the last thirty million years during which our bodies, and our guts in particular, were evolving. In other words, there is very little evidence that our guts are terribly special and the job of a generalist primate gut is primarily to eat pieces of plants. (
source; see also articles by
Grande & Leckie and
Derek Wall)
Then there's this research:
Robert W. Sussman, Ph.D., professor of anthropology, [spoke at] the American Association for the Advancement of the Science's Annual Meeting....[E]arly man was not an aggressive killer, Sussman argues. He poses a new theory, based on the fossil record and living primate species, that primates have been prey for millions of years, a fact that greatly influenced the evolution of early man.
"Our intelligence, cooperation and many other features we have as modern humans developed from our attempts to out-smart the predator," says Sussman.... The idea of "Man the Hunter" is the generally accepted paradigm of human evolution, says Sussman, "It developed from a basic Judeo-Christian ideology of man being inherently evil, aggressive and a natural killer. In fact, when you really examine the fossil and living non-human primate evidence, that is just not the case."
Sussman's research is based on studying the fossil evidence dating back nearly seven million years. "Most theories on Man the Hunter fail to incorporate this key fossil evidence," Sussman says. "We wanted evidence, not just theory. We thoroughly examined literature available on the skulls, bones, footprints and on environmental evidence, both of our hominid ancestors and the predators that coexisted with them." ...
But what Sussman and Hart discovered is that Australopithecus afarensis was not dentally pre-adapted to eat meat. "It didn't have the sharp shearing blades necessary to retain and cut such foods," Sussman says. "These early humans simply couldn't eat meat. If they couldn't eat meat, why would they hunt?"
It was not possible for early humans to consume a large amount of meat until fire was controlled and cooking was possible. Sussman points out that the first tools didn't appear until two million years ago. And there wasn't good evidence of fire until after 800,000 years ago.
Bio-Medicine.org, 2006
Consider also that the Maasai in Kenya, who still eat a diet high in wild hunted meats, have the worst life expectancy in the world. (
Fuhrman)
In any event, the idea that our ancestors might have decided to mimic other animals and eat more meat isn't a particularly compelling argument that it's natural for us to do so. Given that humans act outside of instinct, looking at historical behavior isn't as convincing as looking at anatomy—as we'll do in a moment.
Considering the other primates
Our closest animal relatives are, of course, the other primates. They provide clues about our natural diet since our anatomy is so similar to theirs. Very few of them eat any significant amount of animals, and those who do typically mostly stick to things like insects, not cows, pigs, and chickens. Jane Goodall, famous for her extensive study of apes while living with them, found that it was very rare for the primates she saw to eat other animals. Critics lunge all over the fact that Goodall discovered that primates
occasionally eat meat. But the key word here is
occasionally. If we ate meat is infrequently as the other primates did, our health would certainly be a lot better. Goodall herself apparently wasn't impressed by primates' occasional eating of meat:
Jane Goodall herself is a vegetarian.
Chimpanzee: Eats 95-99% plants, and most of the rest is termites (not meat). (Source:
Creative Commons)
How slight is the other primates' animal consumption? This
article on primate eating habits from Harvard has a bar graph of all the things that chimps and monkeys eat (Fig. 3), and meat isn't even in the chart. What they
do eat is fruit, seeds, leaves, flowers, and pith. There
is a category called "Miscellaneous", which for most species amounts to less than 5% of their diet, and for chimps and redtail monkeys less than 1%. The
Honolulu Zoo gives a slightly higher figure, saying that non-plant consumption is 5% of a chimp's diet, but this includes their main non-plant food, termites. (
Termites are a good source of vitamin B12, by the way). Craig B. Stanford, Ph.D. says, "Chimpanzees are largely fruit eaters, and meat composes only about 3% of the time they spent eating overall, less than in nearly all human societies." (
source) Biologist
Rob Dunn says that chimps eat meat "on average, nine days a year".
Any way you slice it, the chimp diet is at least 95-99% plants.
Which brings up another point: The people who hysterically scream at me that chimps are omnivores, besides ignoring that chimps' meat consumption is so small as to be virtually non-existent, never acknowledge that the non-plant foods chimps eat
are not the same things humans eat. Chimps do
not eat cattle and chickens. And humans don't eat termites. The idea that the meat-laden American diet can be justified because chimps may eat a whopping 5% of non-plant foods, none of it cattle or chickens, and much of it termites, is rather silly.
Let's do the math to see what 1% of a diet as non-plant foods actually looks like. If all of that 1% were beef—which for chimps, it is not—how much beef would that be? For an adult human, it's a mere
8 grams a day (about 1/3 of an ounce, or just 0.02 pounds). That's about
1/9th of a medium carrot. Go get a carrot, cut it into
nine pieces, and each piece then represents the amount of meat (or termites) you could eat every day to have your diet match that of a chimp. Yes, there you have chimps' overwhelming "omnivorism".
Here's how another writer put it:
"Meat makes up only 1.4% of [chimps'] diet which in any statistical study or analysis would be considered as quantitatively unimportant. In longitudinal studies it has been found that 90% of all kills were by males and as the females rarely hunt they receive a share in return by begging only after she allows him to mate with her.... On rare occasions chimps do eat and kill a baby chimp. So if you follow this argument to its conclusion, humans should kill and eat their babies, meat should only make up 1.4% of the human diet, [and] females should only receive meat by begging for it and allowing the giver to mate with her!" (
source)
Consider also that even though primates eat meat sparingly, there again it's likely because they're intelligent and like humans are able to make choices to act outside of instinct. As
other writers put it, "While chimpanzees are known to kill, this behaviour is not necessarily dietary but ritualistic." In 2006 the journal
Nature published research about how chimpanzees have culture—behaviors copied from peers rather than being genetic. (See "
Case Closed: Apes Got Culture".)
Eugene Khutoryansky who does believe that eating meat is natural, still cautions that the implications of chimps' killing should give us pause:
Eating meat is indeed natural in the sense that other animals do it as well. In fact, it is even done on occasion by our closest living relatives, the chimpanzees. However, there are many other things which are also natural. For example, chimpanzee males sometimes rape the females in their tribe. Chimpanzees sometimes engage in organized warfare against other tribes with which they compete for territory. A chimpanzee male, in a moment of rage, sometimes picks up a nearby infant, and crushes his skull against a rock. And chimpanzees do on occasion eat meat, and they do on occasion engage in cannibalism, in spite of the fact that there is a plentiful supply of food from other sources.
So eating meat is indeed absolutely natural. However, the fact that it is natural does not imply that it is ethically permissible. If we believed that eating meat was ethically permissible simply because other animals did it as well, then this would imply that there is nothing wrong with rape, cannibalism, or infanticide, all of which routinely occurs throughout the animal kingdom. (
source)
What it means to be an omnivore
There is no question that humans are capable of eating meat. But that certainly doesn't mean it's ideal for us. As I mentioned earlier, commercial cat foods typically contain rice, corn, and wheat. But of course, cats are true carnivores. We don't call them omnivores just because they'll eat things contrary to what nature intended. That would be silly. No one makes that argument for cats. But they make it for humans, enthusiastically.
McDougall explains how the ability to digest animal foods didn't hurt our survival as a race, although it takes a toll on our lifespan:
"Undoubtedly, all of these [meat-containing] diets were adequate to support growth and life to an age of successful reproduction. To bear and raise offspring you only need to live for 20 to 30 years, and fortuitously, the average life expectancy for these people was just that. The few populations of hunter-gatherers surviving into the 21st Century are confined to the most remote regions of our planet—like the Arctic and the jungles of South America and Africa—some of the most challenging places to manage to survive. Their life expectancy is also limited to 25 to 30 years and infant mortality is 40% to 50%. Hunter-gatherer societies fortunately did survive, but considering their arduous struggle and short lifespan, I would not rank them among successful societies."
The problem with the term "omnivore" is that it's used in different ways. Many folks assert that if a primate
ever eats any meat at all, no matter how small or insignificant, then bam! — they're an omnivore. But cats eat copious amounts of rice, corn, and wheat in commercial cat food, and have far more plants in their diet than meat in primates' diets. So why do these people insist that the piddling, insignificant amount of animal foods consumed by primates makes them omnivores, while cats are carnivores no matter how much plant food they eat?
And once they (think) they've shown that primates are omnivores, they then use this "fact" to justify the
huge amount of meat that people eat today. This of course is ridiculous.
A more reasonable definition would be that a true omnivore would routinely eat large quantities of both plants and animals. A creature consuming less than 5% of its calories from animals just doesn't seem very omnivorous to me. (This includes other primates, our ancestors, and traditional Okinawans.) But for the record, if you insist that such creatures are omnivores, then I'll agree with you — as long as you agree that humans should also eat less than 5% of our calories from animals, just like the other creatures you're basing our "omnivorism" on. And that cats are omnivores, too.
Humans lack a desire to eat whole animals
True carnivores (and omnivores) salivate about the idea of eating whole prey animals when they see them. Humans do not. We're interested in eating the body parts only because they've been removed from the original animal and processed, and because we grew up eating them, making it seem perfectly normal. It's amazing how much of a disconnect we've been able to learn about the difference between animals and food. As
GoVeg puts it:
While carnivores take pleasure in killing animals and eating their raw flesh, any human who killed an animal with his or her bare hands and dug into the raw corpse would be considered deranged. Carnivorous animals are aroused by the scent of blood and the thrill of the chase. Most humans, on the other hand, are revolted by the sight of raw flesh and cannot tolerate hearing the screams of animals being ripped apart and killed. The bloody reality of eating animals is innately repulsive to us, more proof that we were not designed to eat meat.
Ask yourself: When you see dead animals on the side of the road, are you tempted to stop for a snack? Does the sight of a dead bird make you salivate? Do you daydream about killing cows with your bare hands and eating them raw? If you answered "no" to all of these questions, congratulations--you're a normal human herbivore--like it or not. Humans were simply not designed to eat meat. Humans lack both the physical characteristics of carnivores and the instinct that drives them to kill animals and devour their raw carcasses.
And here's one of my favorite passages by
John A. McDougall, M.D.:
Cats are obligate carnivores (they must live on a diet primarily of meat) and their taste buds reflect this by having abandoned the tongue sensors that respond to sweet-tasting carbohydrates. Dogs are omnivores (they have retained both kinds of taste buds) those enjoying carbohydrates and amino acids. Humans tongues respond pleasurably to sweet (carbohydrates), but have lost the taste for amino acids, placing us undeniably in the category of herbivores (plant eaters).
Many of your friends and family are confused, thinking people are omnivores, needing both meat and plants in their diet. We only appear to be omnivorous because we have the ability to "doctor up" meat with salt and sauces (barbecue, sweet and sour, marinara, etc.) sufficiently enough to make it palatable. Prove this for yourself.
The next person you meet head-on who claims meat is "tasty," stop him in his tracks and insist that he eat a large plate of plain, unseasoned, boiled beef or boiled chicken in front of you; note their displeasure. Then offer that same meal to the dog or cat and note how eagerly this critter devours the meat. You would be hard-pressed to find a person who did not enjoy a bowl of perfect, ripe bananas, but try to get your cat to eat this sweet food. I have a Rottweiler dog named Bodega who is a true omnivore and enjoys bananas as much as meat. A careful observer notices that an animal's taste buds are no mistake of nature—they clearly define the proper diet that the animal should eat.
Comparing humans to other animals
Human physiology is strikingly similar to that of other plant-eaters, and quite unlike that of carnivores. It is telling that in none of the missives that readers have sent in to argue with me do they ever deny the data in the following table. They simply think that by making some other point (e.g., that humans possess canine teeth) that somehow obliterates the more convincing data in the table. This is the same table presented at the beginning, but it's important enough that it bears repeating.
Humans are biologically herbivores
Carnivores
Omnivores
Herbivores
Humans
Facial muscles
Reduced to allow wide mouth gape
Reduced
Well-developed
Well-developed
Jaw type
Angle not expanded
Angle not expanded
Expanded angle
Expanded angle
Jaw joint location
On same plane as molar teeth
On same plane as molar teeth
Above the plane of the molars
Above the plane of the molars
Jaw motion
Shearing; minimal side-to-side motion
Shearing; minimal side-to-side motion No shear; good side-to-side, front-to-back
No shear; good side-to-side, front-to-back
Major jaw muscles
Temporalis
Temporalis
Masseter and ptergoids
Masseter and pterygoids
Mouth opening vs. head size
Large
Large
Small
Small
Teeth: Incisors
Short and pointed
Short and pointed
Broad, flattened and spade-shaped
Broad, flattened and spade-shaped
Teeth: Canines
Long, sharp, and curved
Long, sharp and curved
Dull and short or long (for defense), or none
Short and blunted
Teeth: Molars
Sharp, jagged and blade-shaped
Sharp blades and/or flattened
Flattened with cusps vs. complex surface
Flattened with nodular cusps
Chewing
None; swallows food whole
Swallows food whole and/or simple crushing
Extensive chewing necessary
Extensive chewing necessary
Saliva
No digestive enzymes
No digestive enzymes
Carbohydrate digesting enzymes
Carbohydrate digesting enzymes
Stomach type
Simple
Simple
Simple or multiple chambers
Simple
Stomach acidity with food in stomach
≤ pH 1
≤ pH 1
pH 4-5
pH 4-5
Length of small intestine
3-6 times body length
4-6 times body length
10-12+ times body length
10-11 times body length
Colon
Simple, short, and smooth
Simple, short, and smooth
Long, complex; may be sacculated
Long, sacculated
Liver
Can detoxify vitamin A
Can detoxify vitamin A
Cannot detoxify vitamin A
Cannot detoxify vitamin A
Kidney
Extremely concentrated urine
Extremely concentrated urine
Moderately concentrated urine
Moderately concentrated urine
Nails
Sharp claws
Sharp claws
Flattened nails or blunt hooves
Flattened nails
From
The Comparative Anatomy of Eating, by Milton R. Mills, M.D. * "Body length" measured from neck to anus, as with the other animals
As another writer said, "The human body was not designed to catch or eat animals. You have no claws. Your teeth do not rend flesh. Your mouth can not seriously wound nor is it made to really get a good bite into a struggling victim like true carnivores can. You are not fit to run fast to catch prey. Meat-eaters have fast enough reflexes to ambush or overtake a victim. You do not. Try catching a pig or a chicken with your bare hands; see what happens."
Plant-eaters have the longest lifespans
In general,
plant-eating creatures have the longest lifespans. Elephants, horses, and chimpanzees are at the top of the list while lions, tigers, and wolves are about half that. Humans' lifespans are even longer than the elephants etc. (even before modern medicine), providing more evidence that we're in the plant-eating camp.
Omnivores
Herbivores (least sleep)
Carnivores (most sleep)
We sleep like herbivores
Carnivores sleep the most, herbivores the least, and omnivores in the middle. Guess which group our own sleep correlates to. Here are some charts from
an article in Nature (PDF). They have arbitrarily stuck us (and other primates) in the omnivore group, because that's what everyone assumes we are, but notice that we're at the extreme end of that chart, with nearly every other single omnivore sleeping more than we do. We fit nicely in the herbivore chart, and I added a prominent dot for us in that one so you can see how we fit in at eight hours a night. If we use a figure of 6-7 hours a night (suggested as natural by
longevity research), our placement in the chart becomes even more compelling.
"But what about canine teeth and binocular vision?"
It's part of our collective consciousness that we have "canine teeth" and that this "proves" that we're meat eaters. But the truth is that this argument couldn't be weaker.
Canine teeth are canine in name only.Humans' so-called "canine teeth" are unlike the canine teeth of
actual canines, which are
really long and really pointed. Our teeth are absolutely not like theirs. In fact,
other vegetarian animals (like gorillas and horses) possess the same so-called "canine" teeth.
Overall, our teeth resemble those of plant-eaters much more than meat-eaters. For example, we have molar teeth (plant-eaters do, carnivores don't). Try to find a human-type molar inside your cat's mouth. Our teeth can also move side to side to grind, just like the other plant-eaters, and completely unlike the carnivores. Their jaws go only up and down.
My favorite counter to someone trying the canine rationalization on a message board:
"Hey Julia--we evolved with canine teeth? I'd like to see you tackle a steer and tear it apart with those ferocious incisors."
What's funny to me is how the teeth argument is
so important to meat proponents when they make their point about canine teeth, and then as soon as they find out that our teeth are much more similar to those of herbivores than of carnivores, and therefore consideration of our teeth suggests that we're designed to be plant eaters -- suddenly what kind of teeth we have is not so important to them after all.
Others have argued that predators have eyes on the front of their heads for binocular vision, while prey animals have eyes on the sides, indicating that we fall into the predator camp. This ignores the fact that the animals that we're
most similar to -- the other primates -- have eyes on the front of their heads, and are almost exclusively vegetarian. It's also important to remember what I said at the top of this article: There is certainly evidence on both sides of this debate, but the
preponderance of evidence clearly shows that we're suited to eating plants almost exclusively.
Does the unhealthfulness of meat mean that it's not natural?
The medical evidence is overwhelming: The more animal foods we eat, the more heart disease, cancer, diabetes, and other degenerative disease we suffer. This has been exhaustively demonstrated beyond any doubt. Dean Ornish, M.D. showed that
heart disease can be reversed, and he did so by feeding his patients a vegetarian diet.
John McDougall, M.D. has also written extensively about how the overwhelming scientific evidence shows that animal foods cause disease, and how for 25 years he's helped patients regain their health by eating unprocessed vegan foods instead. The science journals are filled with articles that come to the same conclusion: more plants means better health, more animal foods means more illness. And as mentioned earlier, the Maasai in Kenya, who still eat a diet high in wild hunted meats, have the worst life expectancy in the world. (
Fuhrman)
But is this evidence that meat-eating is unnatural? Maybe so, but maybe not. On the one hand we expect that's what's natural for us to eat should keep us in the best health (and that would discount meat, at least in the amounts it would take to make us true omnivores). But on the other hand, people can certainly live well beyond their reproductive years on a mixed animal-plant diet, which is mostly what evolution cares about. So it's hard to say whether the unhealthfulness of meat is evidence that we're naturally plant-eaters, but then again, we have other, better evidence anyway. The best evidence that we're supposed to eat primarily plants is the obvious one: our anatomy.
Human performance on meat-free diets
Not only do vegetarians and vegans easily build muscle, they often excel as athletes too, winning Olympic gold medals and world championships. In fact, some of the most famous bodybuilders in history were vegetarian. Here's a list of vegan and vegetarian athletes.
Examples of successful vegetarian and vegan athletes
(Note: As of July 2012, I've stopped adding to this list, because I've made my point that there are numerous vegans who among the top athletes in their sports. The number of vegetarian and vegan athletes is growing rapidly now and there's no way I'll be able to keep up with all the new ones. By the way, not all these athletes were/are exclusively veg*n for their entire athletic careers, the point is that they were/are successful as athletes even when veg*n.)
Vegan Bodybuilders
Some sites for vegan bodybuilders:
Vegan bodybuilders shatter the myth that vegans are skinny and malnourished.
(Pictured: Avi Lehyani, anonymous, Ryan Wilson, Robert Cheeke)
Vegan Powerlifters
- Noah Hannibal. Gold medal, heavyweight division of the Australian National Bench Press Championships
- Pat Reeves. 12-time British Masters Powerlifting champion
- Bill Mannetti. 1st place in division, Connecticut State Powerlifting Championship
- Joy Bush. 1st place in division, Connecticut State Powerlifting Championship
- Andrew Clark. 1st place in division, Global One IPF
- Joel Kirkilis. 1st place in division, Global One IPF and ANB Victorian Championships
- Patrick Virtue. 2nd place in division, Global One IPF
Other Vegan Athletes
- Carl Lewis (track) 2 Olympic gold medals as a vegan
- Scott Jurek (ultramarathoner) 7 consecutive wins at Western States 100 Mile Endurance Run, numerous other first place finishes and records
- Matt Frazier (ultramarathoner), runs NoMeatAthlete.com
- Scott Spitz (runner) Numerous 1st place finishes
- Tim VanOrden (runner) Numerous 1st place finishes
- Fiona Oakes (runner) 1st place woman and 2nd overall in a 2011 marathon
- Brendan Brazier (Ironman triathlete). Won the National 50km Ultra Marathon Championships
- Ruth Heidrich, (triathlete and marathoner) More than 900 first-place trophies and set several performance records. Named One of the 10 Fittest Women in North America.
- Dave Scott (Ironman triathlete) Six-time Ironman champion
Vegetarian Athletes
- Billy Simmonds (bodybuilder) Natural Universe champion
- Bill Pearl (bodybuilder) Mr. Universe (3 times), World's Best Built Man, Mr. America, Mr. California, numerous Halls of Fame
- Roy Hilligenn (bodybuilder) Mr. South Africa (4x), Mr. America, Olympic lifter
- Ricky Williams (football) Miami Dolphins
Amateur Vegan Athletes of note (except vegetarian where noted)
- Vegan Bodybuilders: Ryan Wilson, Ivan, Mike Mahler, Marvin Whittred, Jon Hinds, Charlie Abel, Mike Mahler: "Becoming a vegan had a profound effect on my training. … [M]y bench press excelled past 315 pounds...and I put on 10 pounds of lean muscle in a few months."
- Dan Attanasio (extreme calisthenics)
- Mike Eves (IKFF certified kettlebell trainer)
- Jeanie & Chelsea Ward-Waller, Stephanie Palmer. Bicycled coast-to-coast across the U.S. in 2012 to support safe bicycle routes in cities. They mentioned that they're vegetarian in a presentation I attended in March 2012.
- Jane Ward, M.D. Described herself as mostly vegan at a presentation I attended in March 2012. At age 60 in 2012, in the last four years she completed over 10 triathlons including a Half-Ironman, and is also a veteran of over 8 marathons and the 24 hour/50 mile Caledonian Challenge in Scotland.
- Michael Bluejay. I'm listing myself not because I'm an elite athlete (I'm not), but just to show that I put my money where my mouth is. As a vegan, I used to run marathons, and before a knee injury ruined my running career, my half-marathon time put me in the top 22% of male runners my age. After my injury, I started doing handcycle marathons. I won the handcycle division of the 2012 Austin Marathon, but there were no other entrants in my division. I hope to win next year's race against actual competition.
In this video, McDougall notes that
Roman gladiators were vegan.
The research on veg vs. non-veg athletes is fairly sparse, but what does exist has failed to show any clear performance benefit for meat-eaters. (See my separate article,
Protein and Strength.)
Summary
- Human anatomy is much more similar to herbivores than carnivores.
- If humans are omnivores because we're capable of eating meat, then so are cats, since most cats eat plant foods every day. If we're supposed to eat animal foods, the evidence suggests it's a tiny part of our diets, not a large one.
- Making one contrary point does not magically invalidate all the other evidence as soon as it's made.
http://michaelbluejay.com/veg/natural.html
much more mobile and allows the complex jaw motionsneeded when chewing plant foods. Additionally, this typeof jaw joint allows the upper and lower cheek teeth to cometogether along the length of the jaw more or less at once when the mouth is closed in order to form grinding plat-forms. (This type of joint is so important to a plant-eatinganimal, that it is believed to have evolved at least 15 differ-ent times in various plant-eating mammalian species.) Theangle of the mandible has expanded to provide a broadarea of attachment for the well-developed masseter andpterygoid muscles (these are the major muscles of chewingin plant-eating animals). The temporalis muscle is small andof minor importance. The masseter and pterygoid muscleshold the mandible in a sling-like arrangement and swing thejaw from side-to-side. Accordingly, the lower jaw of plant-eating mammals has a pronounced sideways motion wheneating. This lateral movement is necessary for the grindingmotion of chewing.The dentition of herbivores is quite varied dependingon the kind of vegetation a particular species is adapted toeat. Although these animals differ in the types and numbersof teeth they possess, the various kinds of teeth when pre-sent, share common structural features. The incisors arebroad, flattened and spade-like. Canines may be small as inhorses, prominent as in hippos, pigs and some primates(these are thought to be used for defense) or absent alto-gether. The molars, in general, are squared and flattened ontop to provide a grinding surface. The molars cannot verti-cally slide past one another in a shearing/slicing motion, butthey do horizontally slide across one another to crush andgrind. The surface features of the molars vary depending onthe type of plant material the animal eats. The teeth of her-bivorous animals are closely grouped so that the incisorsform an efficient cropping/biting mechanism, and the upperand lower molars form extended platforms for crushing andgrinding. The “walled-in” oral cavity has a lot of potentialspace that is realized during eating.These animals carefully and methodically chew theirfood, pushing the food back and forth into the grindingteeth with the tongue and cheek muscles. This thoroughprocess is necessary to mechanically disrupt plant cell wallsin order to release the digestible intracellular contents andensure thorough mixing of this material with their saliva.This is important because the saliva of plant-eating mam-mals often contains carbohydrate-digesting enzymes whichbegin breaking down food molecules while the food is stillin the mouth.
Stomach and Small Intestine
Striking differences between carnivores and herbivores areseen in these organs. Carnivores have a capacious simple(single-chambered) stomach. The stomach volume of a car-nivore represents 60-70% of the total capacity of the diges-tive system. Because meat is relatively easily digested, theirsmall intestines (where absorption of food molecules takesplace) are short—about three to five or six times the body length. Since these animals average a kill only about once a week, a large stomach volume is advantageous because itallows the animals to quickly gorge themselves when eat-ing, taking in as much meat as possible at one time whichcan then be digested later while resting. Additionally, theability of the carnivore stomach to secrete hydrochloric acidis exceptional. Carnivores are able to keep their gastric pHdown around 1-2 even with food present. This is necessary to facilitate protein breakdown and to kill the abundantdangerous bacteria often found in decaying flesh foods.Because of the relative difficulty with which variouskinds of plant foods are broken down (due to largeamounts of indigestible fibers), herbivores have significant-ly longer and in some cases, far more elaborate guts thancarnivores. Herbivorous animals that consume plants con-taining a high proportion of cellulose must “ferment” (digestby bacterial enzyme action) their food to obtain the nutrient value. They are classified as either “ruminants” (foregut fer-menters) or hindgut fermenters. The ruminants are the
The saliva of carnivorous animalsdoes not contain digestive enzymes.Human saliva contains the carbohy-drate–digesting enzyme, salivary amylase. This enzyme is responsiblefor the majority of starch digestion.
”“
plant-eating animals with the celebrated multiple-chamberedstomachs. Herbivorous animals that eat a diet of relatively soft vegetation do not need a multiple-chambered stomach.They typically have a simple stomach, and a long smallintestine. These animals ferment the difficult-to-digestfibrous portions of their diets in their hindguts (colons).Many of these herbivores increase the sophistication andefficiency of their GI tracts by including carbohydrate-digest-ing enzymes in their saliva. A multiple-stomach fermentationprocess in an animal which consumed a diet of soft, pulpy vegetation would be energetically wasteful. Nutrients andcalories would be consumed by the fermenting bacteria andprotozoa before reaching the small intestine for absorption.The small intestine of plant-eating animals tends to be very long (greater than 10 times body length) to allow adequatetime and space for absorption of the nutrients.
Colon
The large intestine (colon) of carnivores is simple and very short, as its only purposes are to absorb salt and water. It isapproximately the same diameter as the small intestine and,consequently, has a limited capacity to function as a reser- voir. The colon is short and non-pouched. The muscle is dis-tributed throughout the wall, giving the colon a smoothcylindrical appearance. Although a bacterial population ispresent in the colon of carnivores, its activities are essen-tially putrefactive.In herbivorous animals, the large intestine tends to be ahighly specialized organ involved in water and electrolyteabsorption, vitamin production and absorption, and/or fer-mentation of fibrous plant materials. The colons of herbi- vores are usually wider than their small intestine and are rel-atively long. In some plant-eating mammals, the colon has apouched appearance due to the arrangement of the musclefibers in the intestinal wall. Additionally, in some herbivoresthe cecum (the first section of the colon) is quite large andserves as the primary or accessory fermentation site.
What About Omnivores?
One would expect an omnivore to show anatomical features which equip it to eat both animal and plant foods. According to evolutionary theory, carnivore gut structure|is more primitive than herbivorous adaptations. Thus,an omnivore might be expected to be a carnivore whichshows some gastrointestinal tract adaptations to an herbivo-rous diet.This is exactly the situation we find in the Bear,Raccoon and certain members of the Canine families. (Thisdiscussion will be limited to bears because they are, in gen-eral, representative of the anatomical omnivores.) Bears areclassified as carnivores but are classic anatomical omnivores. Although they eat some animal foods, bears are primarily herbivorous with 70-80% of their diet comprised of plantfoods. (The one exception is the Polar bear which lives inthe frozen, vegetation poor arctic and feeds primarily on sealblubber.) Bears cannot digest fibrous vegetation well, andtherefore, are highly selective feeders. Their diet is dominat-ed by primarily succulent lent herbage, tubers and berries.Many scientists believe the reason bears hibernate isbecause their chief food (succulent vegetation) not availablein the cold northern winters. (Interestingly, Polar bearshibernate during the summer months when seals areunavailable.)In general, bears exhibit anatomical features consistent with a carnivorous diet. The jaw joint of bears is in the sameplane as the molar teeth. The temporalis muscle is massive,and the angle of the mandible is small corresponding to thelimited role the pterygoid and masseter muscles play inoperating the jaw. The small intestine is short ( less than fivetimes body length) like that of the pure carnivores, and thecolon is simple, smooth and short. The most prominentadaptation to an herbivorous diet in bears (and other“anatomical” omnivores) is the modification of their denti-tion. Bears retain the peg-like incisors, large canines andshearing premolars of a carnivore; but the molars havebecome squared with rounded cusps for crushing and grind-ing. Bears have not, however, adopted the flattened, bluntnails seen in most herbivores and retain the elongated,pointed claws of a carnivore. An animal which captures, kills and eats prey must havethe physical equipment which makes predation practicaland efficient. Since bears include significant amounts of meat in their diet, they must retain the anatomical featuresthat permit them to capture and kill prey animals. Hence,bears have a jaw structure, musculature and dentition whichenable them to develop and apply the forces necessary tokill and dismember prey even though the majority of theirdiet is comprised of plant foods. Although an herbivore-stylejaw joint (above the plane of the teeth) is a far more efficientjoint for crushing and grinding vegetation and would poten-tially allow bears to exploit a wider range of plant foods intheir diet, it is a much weaker joint than the hinge-style car-nivore joint. The herbivore-style jaw joint is relatively easily dislocated and would not hold up well under the stresses of
subduing struggling prey and/or crushing bones (nor wouldit allow the wide gape carnivores need). In the wild, an ani-mal with a dislocated jaw would either soon starve to deathor be eaten by something else and would, therefore, beselected against. A given species cannot adopt the weakerbut more mobile and efficient herbivore-style joint until ithas committed to an essentially plant-food diet test it riskjaw dislocation, death and ultimately, extinction.
What About Me?
The human gastrointestinal tract features the anatomicalmodifications consistent with an herbivorous diet. Humanshave muscular lips and a small opening into the oral cavity.Many of the so-called “muscles of expression” are actually the muscles used in chewing. The muscular and agiletongue essential for eating, has adapted to use in speechand other things. The mandibular joint is flattened by a car-tilaginous plate and is located well above the plane of theteeth. The temporalis muscle is reduced. The characteristic“square jaw” of adult males reflects the expanded angularprocess of the mandible and the enlarged masseter/ptery-goid muscle group. The human mandible can move forwardto engage the incisors, and side-to-side to crush and grind.Human teeth are also similar to those found in otherherbivores with the exception of the canines (the canines of some of the apes are elongated and are thought to be usedfor display and/or defense). Our teeth are rather large andusually abut against one another. The incisors are flat andspade-like, useful for peeling, snipping and biting relatively soft materials. The canines are neither serrated nor conical,but are flattened, blunt and small and function Like incisors.The premolars and molars are squarish, flattened and nodu-lar, and used for crushing, grinding and pulping non-coarsefoods.Human saliva contains the carbohydrate-digestingenzyme, salivary amylase. This enzyme is responsible forthe majority of starch digestion. The esophagus is narrow and suited to small, soft balls of thoroughly chewed food.Eating quickly, attempting to swallow a large amount of food or swallowing fibrous and/or poorly chewed food(meat is the most frequent culprit) often results in chokingin humans.Man’s stomach is single-chambered, but only moder-ately acidic. (Clinically, a person presenting with a gastricpH less than 4-5 when there is food in the stomach is causefor concern.) The stomach volume represents about 21-27%of the total volume of the human GI tract. The stomachserves as a mixing and storage chamber, mixing and lique-fying ingested foodstuffs and regulating their entry into thesmall intestine. The human small intestine is long, averagingfrom 10 to 11 times the body length. (Our small intestineaverages 22 to 30 feet in length. Human body size is mea-sured from the top of the head to end of the spine and aver-ages between two to three feet in length in normal-sizedindividuals.)The human colon demonstrates the pouched structurepeculiar to herbivores. The distensible large intestine is larg-er in cross-section than the small intestine, and is relatively long. Man’s colon is responsible for water and electrolyteabsorption and vitamin production and absorption. There isalso extensive bacterial fermentation of fibrous plant mate-rials, with the production and absorption of significantamounts of food energy (volatile short-chain fatty acids)depending upon the fiber content of the diet. The extent to which the fermentation and absorption of metabolites takesplace in the human colon has only recently begun to beinvestigated.In conclusion, we see that human beings have the gas-trointestinal tract structure of a “committed” herbivore.Humankind does not show the mixed structural featuresone expects and finds in anatomical omnivores such asbears and raccoons. Thus, from comparing the gastroin-testinal tract of humans to that of carnivores, herbivores andomnivores we must conclude that humankind’s GI tract isdesigned for a purely plant-food diet.
The large intestine (colon) of carni- vores is simple and very short…thecolons of herbivores are usually wider than their small intestine andare relatively long.
”“
FACIAL MUSCLES
CarnivoreReduced to allow wide mouth gapeHerbivoreWell-developedOmnivoreReducedHumanWell-developed
JAW TYPE
CarnivoreAngle not expandedHerbivoreExpanded angleOmnivoreAngle not expandedHumanExpanded angle
JAW JOINT LOCATION
CarnivoreOn same plane as molar teethHerbivoreAbove the plane of the molarsOmnivoreOn same plane as molar teethHumanAbove the plane of the molars
JAW MOTION
CarnivoreShearing; minimal side-to-side motionHerbivoreNo shear; good side-to-side, front-to-back OmnivoreShearing; minimal side-to-sideHumanNo shear; good side-to-side, front-to-back
MAJOR JAW MUSCLES
CarnivoreTemporalisHerbivoreMasseter and pterygoidsOmnivoreTemporalisHumanMasseter and pterygoids
MOUTH OPENING vs. HEAD SIZE
CarnivoreLargeHerbivoreSmallOmnivoreLargeHumanSmall
TEETH (INCISORS)
CarnivoreShort and pointedHerbivoreBroad, flattened and spade shapedOmnivoreShort and pointedHumanBroad, flattened and spade shaped
TEETH (CANINES)
CarnivoreLong, sharp and curvedHerbivoreDull and short or long (for defense), or noneOmnivoreLong, sharp and curvedHumanShort and blunted
TEETH (MOLARS)
CarnivoreSharp, jagged and blade shapedHerbivoreFlattened with cusps vs complex surfaceOmnivoreSharp blades and/or flattenedHumanFlattened with nodular cusps
CHEWING
CarnivoreNone; swallows food wholeHerbivoreExtensive chewing necessary OmnivoreSwallows food whole and/or simple crushingHumanExtensive chewing necessary
Summary
SALIVA
CarnivoreNo digestive enzymesHerbivoreCarbohydrate digesting enzymesOmnivoreNo digestive enzymesHumanCarbohydrate digesting enzymes
STOMACH TYPE
CarnivoreSimpleHerbivoreSimple or multiple chambersOmnivoreSimpleHumanSimple
STOMACH ACIDITY
CarnivoreLess than or equal to pH 1 with food in stomachHerbivorepH 4 to 5 with food in stomachOmnivoreLess than or equal to pH 1 with food in stomachHumanpH 4 to 5 with food in stomach
STOMACH CAPACITY
Carnivore60% to 70% of total volume of digestive tract HerbivoreLess than 30% of total volume of digestive tract Omnivore60% to 70% of total volume of digestive tract Human21% to 27% of total volume of digestive tract
LENGTH OF SMALL INTESTINE
Carnivore3 to 6 times body lengthHerbivore10 to more than 12 times body lengthOmnivore4 to 6 times body lengthHuman10 to 11 times body length
COLON
CarnivoreSimple, short and smoothHerbivoreLong, complex; may be sacculatedOmnivoreSimple, short and smoothHumanLong, sacculated
LIVER
CarnivoreCan detoxify vitamin AHerbivoreCannot detoxify vitamin AOmnivoreCan detoxify vitamin AHumanCannot detoxify vitamin A
KIDNEY
CarnivoreExtremely concentrated urineHerbivoreModerately concentrated urineOmnivoreExtremely concentrated urineHumanModerately concentrated urine
NAILS
CarnivoreSharp clawsHerbivoreFlattened nails or blunt hoovesOmnivoreSharp clawsHumanFlattened nails
https://www.scribd.com/doc/94656/The-Comparative-Anatomy-of-Eating
