Health

 

The Comparative Anatomy of Eating

Milton R. Mills, M.D. | 11/21/09

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Read More: anatomy, carnivore, comparative anatomy of eating, herbivore, milton mills, omnivore

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Humans are most often described as "omnivores." This classification is based on the "observation" that humans generally eat a wide variety of plant and animal foods. However, culture, custom and training are confounding variables when looking at human dietary practices. Thus, "observation" is not the best technique to use when trying to identify the most "natural" diet for humans. While most humans are clearly "behavioral" omnivores, the question still remains as to whether humans are anatomically suited for a diet that includes animal as well as plant foods.

A better and more objective technique is to look at human anatomy and physiology. Mammals are anatomically and physiologically adapted to procure and consume particular kinds of diets. (It is common practice when examining fossils of extinct mammals to examine anatomical features to deduce the animal's probable diet.) Therefore, we can look at mammalian carnivores, herbivores (plant-eaters) and omnivores to see which anatomical and physiological features are associated with each kind of diet. Then we can look at human anatomy and physiology to see in which group we belong.

Oral Cavity

Carnivores have a wide mouth opening in relation to their head size. This confers obvious advantages in developing the forces used in seizing, killing and dismembering prey. Facial musculature is reduced since these muscles would hinder a wide gape, and play no part in the animal's preparation of food for swallowing. In all mammalian carnivores, the jaw joint is a simple hinge joint lying in the same plane as the teeth. This type of joint is extremely stable and acts as the pivot point for the "lever arms" formed by the upper and lower jaws. The primary muscle used for operating the jaw in carnivores is the temporalis muscle. This muscle is so massive in carnivores that it accounts for most of the bulk of the sides of the head (when you pet a dog, you are petting its temporalis muscles). The "angle" of the mandible (lower jaw) in carnivores is small. This is because the muscles (masseter and pterygoids) that attach there are of minor importance in these animals. The lower jaw of carnivores cannot move forward, and has very limited side-to-side motion. When the jaw of a carnivore closes, the blade-shaped cheek molars slide past each other to give a slicing motion that is very effective for shearing meat off bone.

The teeth of a carnivore are discretely spaced so as not to trap stringy debris. The incisors are short, pointed and prong-like and are used for grasping and shredding. The canines are greatly elongated and dagger-like for stabbing, tearing and killing prey. The molars (carnassials) are flattened and triangular with jagged edges such that they function like serrated-edged blades. Because of the hinge-type joint, when a carnivore closes its jaw, the cheek teeth come together in a back-to-front fashion giving a smooth cutting motion like the blades on a pair of shears.

The saliva of carnivorous animals does not contain digestive enzymes. When eating, a mammalian carnivore gorges itself rapidly and does not chew its food. Since proteolytic (protein-digesting) enzymes cannot be liberated in the mouth due to the danger of autodigestion (damaging the oral cavity), carnivores do not need to mix their food with saliva; they simply bite off huge chunks of meat and swallow them whole.

According to evolutionary theory, the anatomical features consistent with an herbivorous diet represent a more recently derived condition than that of the carnivore. Herbivorous mammals have well-developed facial musculature, fleshy lips, a relatively small opening into the oral cavity and a thickened, muscular tongue. The lips aid in the movement of food into the mouth and, along with the facial (cheek) musculature and tongue, assist in the chewing of food. In herbivores, the jaw joint has moved to position above the plane of the teeth. Although this type of joint is less stable than the hinge-type joint of the carnivore, it is much more mobile and allows the complex jaw motions needed when chewing plant foods. Additionally, this type of jaw joint allows the upper and lower cheek teeth to come together along the length of the jaw more or less at once when the mouth is closed in order to form grinding platforms. (This type of joint is so important to a plant-eating animal, that it is believed to have evolved at least 15 different times in various plant-eating mammalian species.) The angle of the mandible has expanded to provide a broad area of attachment for the well-developed masseter and pterygoid muscles (these are the major muscles of chewing in plant-eating animals). The temporalis muscle is small and of minor importance. The masseter and pterygoid muscles hold the mandible in a sling-like arrangement and swing the jaw from side-to-side. Accordingly, the lower jaw of plant-eating mammals has a pronounced sideways motion when eating. This lateral movement is necessary for the grinding motion of chewing.

The dentition of herbivores is quite varied depending on the kind of vegetation a particular species is adapted to eat. Although these animals differ in the types and numbers of teeth they posses, the various kinds of teeth when present, share common structural features. The incisors are broad, flattened and spade-like. Canines may be small as in horses, prominent as in hippos, pigs and some primates (these are thought to be used for defense) or absent altogether. The molars, in general, are squared and flattened on top to provide a grinding surface. The molars cannot vertically slide past one another in a shearing/slicing motion, but they do horizontally slide across one another to crush and grind. The surface features of the molars vary depending on the type of plant material the animal eats. The teeth of herbivorous animals are closely grouped so that the incisors form an efficient cropping/biting mechanism, and the upper and lower molars form extended platforms for crushing and grinding. The "walled-in" oral cavity has a lot of potential space that is realized during eating.

These animals carefully and methodically chew their food, pushing the food back and forth into the grinding teeth with the tongue and cheek muscles. This thorough process is necessary to mechanically disrupt plant cell walls in order to release the digestible intracellular contents and ensure thorough mixing of this material with their saliva. This is important because the saliva of plant-eating mammals often contains carbohydrate-digesting enzymes which begin breaking down food molecules while the food is still in the mouth.

Stomach and Small Intestine

Striking differences between carnivores and herbivores are seen in these organs. Carnivores have a capacious simple (single-chambered) stomach. The stomach volume of a carnivore represents 60-70% of the total capacity of the digestive system. Because meat is relatively easily digested, their small intestines (where absorption of food molecules takes place) are short&151;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 it allows the animals to quickly gorge themselves when eating, taking in as much meat as possible at one time which can then be digested later while resting. Additionally, the ability of the carnivore stomach to secrete hydrochloric acid is exceptional. Carnivores are able to keep their gastric pH down around 1-2 even with food present. This is necessary to facilitate protein breakdown and to kill the abundant dangerous bacteria often found in decaying flesh foods.

Because of the relative difficulty with which various kinds of plant foods are broken down (due to large amounts of indigestible fibers), herbivores have significantly longer and in some cases, far more elaborate guts than carnivores. Herbivorous animals that consume plants containing a high proportion of cellulose must "ferment" (digest by bacterial enzyme action) their food to obtain the nutrient value. They are classified as either "ruminants" (foregut fermenters) or hindgut fermenters. The ruminants are the plant-eating animals with the celebrated multiple-chambered stomachs. 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 small intestine. These animals ferment the difficult-to-digest fibrous portions of their diets in their hindguts (colons). Many of these herbivores increase the sophistication and efficiency of their GI tracts by including carbohydrate-digesting enzymes in their saliva. A multiple-stomach fermentation process in an animal which consumed a diet of soft, pulpy vegetation would be energetically wasteful. Nutrients and calories would be consumed by the fermenting bacteria and protozoa 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 adequate time 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 is approximately the same diameter as the small intestine and, consequently, has a limited capacity to function as a reservoir. The colon is short and non-pouched. The muscle is distributed throughout the wall, giving the colon a smooth cylindrical appearance. Although a bacterial population is present in the colon of carnivores, its activities are essentially putrefactive.

In herbivorous animals, the large intestine tends to be a highly specialized organ involved in water and electrolyte absorption, vitamin production and absorption, and/or fermentation of fibrous plant materials. The colons of herbivores are usually wider than their small intestine and are relatively long. In some plant-eating mammals, the colon has a pouched appearance due to the arrangement of the muscle fibers in the intestinal wall. Additionally, in some herbivores the cecum (the first section of the colon) is quite large and serves 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 which shows some gastrointestinal tract adaptations to an herbivorous diet.

This is exactly the situation we find in the Bear, Raccoon and certain members of the Canine families. (This discussion will be limited to bears because they are, in general, representative of the anatomical omnivores.) Bears are classified 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 plant foods. (The one exception is the Polar bear which lives in the frozen, vegetation poor arctic and feeds primarily on seal blubber.) Bears cannot digest fibrous vegetation well, and therefore, are highly selective feeders. Their diet is dominated by primarily succulent lent herbage, tubers and berries. Many scientists believe the reason bears hibernate is because their chief food (succulent vegetation) not available in the cold northern winters. (Interestingly, Polar bears hibernate during the summer months when seals are unavailable.)

In general, bears exhibit anatomical features consistent with a carnivorous diet. The jaw joint of bears is in the same plane as the molar teeth. The temporalis muscle is massive, and the angle of the mandible is small corresponding to the limited role the pterygoid and masseter muscles play in operating the jaw. The small intestine is short (less than five times body length) like that of the pure carnivores, and the colon is simple, smooth and short. The most prominent adaptation to an herbivorous diet in bears (and other "anatomical" omnivores) is the modification of their dentition. Bears retain the peg-like incisors, large canines and shearing premolars of a carnivore; but the molars have become squared with rounded cusps for crushing and grinding. Bears have not, however, adopted the flattened, blunt nails seen in most herbivores and retain the elongated, pointed claws of a carnivore.

An animal which captures, kills and eats prey must have the physical equipment which makes predation practical and efficient. Since bears include significant amounts of meat in their diet, they must retain the anatomical features that permit them to capture and kill prey animals. Hence, bears have a jaw structure, musculature and dentition which enable them to develop and apply the forces necessary to kill and dismember prey even though the majority of their diet is comprised of plant foods. Although an herbivore-style jaw joint (above the plane of the teeth) is a far more efficient joint for crushing and grinding vegetation and would potentially allow bears to exploit a wider range of plant foods in their diet, it is a much weaker joint than the hinge-style carnivore 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 would it allow the wide gape carnivores need). In the wild, an animal with a dislocated jaw would either soon starve to death or be eaten by something else and would, therefore, be selected against. A given species cannot adopt the weaker but more mobile and efficient herbivore-style joint until it has committed to an essentially plant-food diet test it risk jaw dislocation, death and ultimately, extinction.

What About Me?

The human gastrointestinal tract features the anatomical modifications consistent with an herbivorous diet. Humans have 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 agile tongue essential for eating, has adapted to use in speech and other things. The mandibular joint is flattened by a cartilaginous plate and is located well above the plane of the teeth. The temporalis muscle is reduced. The characteristic "square jaw" of adult males reflects the expanded angular process of the mandible and the enlarged masseter/pterygoid muscle group. The human mandible can move forward to engage the incisors, and side-to-side to crush and grind.

Human teeth are also similar to those found in other herbivores with the exception of the canines (the canines of some of the apes are elongated and are thought to be used for display and/or defense). Our teeth are rather large and usually abut against one another. The incisors are flat and spade-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 nodular, and used for crushing, grinding and pulping noncoarse foods.

Human saliva contains the carbohydrate-digesting enzyme, salivary amylase. This enzyme is responsible for the 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 choking in humans.

Man's stomach is single-chambered, but only moderately acidic. (Clinically, a person presenting with a gastric pH less than 4-5 when there is food in the stomach is cause for concern.) The stomach volume represents about 21-27% of the total volume of the human GI tract. The stomach serves as a mixing and storage chamber, mixing and liquefying ingested foodstuffs and regulating their entry into the small intestine. The human small intestine is long, averaging from 10 to 11 times the body length. (Our small intestine averages 22 to 30 feet in length. Human body size is measured from the top of the head to end of the spine and averages between two to three feet in length in normal-sized individuals.)

The human colon demonstrates the pouched structure peculiar to herbivores. The distensible large intestine is larger in cross-section than the small intestine, and is relatively long. Man's colon is responsible for water and electrolyte absorption and vitamin production and absorption. There is also extensive bacterial fermentation of fibrous plant materials, with the production and absorption of significant amounts 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 takes place in the human colon has only recently begun to be investigated.

In conclusion, we see that human beings have the gastrointestinal tract structure of a "committed" herbivore. Humankind does not show the mixed structural features one expects and finds in anatomical omnivores such as bears and raccoons. Thus, from comparing the gastrointestinal tract of humans to that of carnivores, herbivores and omnivores we must conclude that humankind's GI tract is designed for a purely plant-food diet.

SUMMARY

Facial Muscles
Carnivore Reduced to allow wide mouth gape
Herbivore Well-developed
Omnivore Reduced
Human Well-developed
 
Jaw Type
Carnivore Angle not expanded
Herbivore Expanded angle
Omnivore Angle not expanded
Human Expanded angle
 
Jaw Joint Location
Carnivore On same plane as molar teeth
Herbivore Above the plane of the molars
Omnivore On same plane as molar teeth
Human Above the plane of the molars
 
Jaw Motion
Carnivore Shearing; minimal side-to-side motion
Herbivore No shear; good side-to-side, front-to-back
Omnivore Shearing; minimal side-to-side
Human No shear; good side-to-side, front-to-back
 
Major Jaw Muscles
Carnivore Temporalis
Herbivore Masseter and pterygoids
Omnivore Temporalis
Human Masseter and pterygoids
 
Mouth Opening vs. Head Size
Carnivore Large
Herbivore Small
Omnivore Large
Human Small
 
Teeth (Incisors)
Carnivore Short and pointed
Herbivore Broad, flattened and spade shaped
Omnivore Short and pointed
Human Broad, flattened and spade shaped
 
Teeth (Canines)
Carnivore Long, sharp and curved
Herbivore Dull and short or long (for defense), or none
Omnivore Long, sharp and curved
Human Short and blunted
 
Teeth (Molars)
Carnivore Sharp, jagged and blade shaped
Herbivore Flattened with cusps vs complex surface
Omnivore Sharp blades and/or flattened
Human Flattened with nodular cusps
 
Chewing
Carnivore None; swallows food whole
Herbivore Extensive chewing necessary
Omnivore Swallows food whole and/or simple crushing
Human Extensive chewing necessary
 
Saliva
Carnivore No digestive enzymes
Herbivore Carbohydrate digesting enzymes
Omnivore No digestive enzymes
Human Carbohydrate digesting enzymes
 
Stomach Type
Carnivore Simple
Herbivore Simple or multiple chambers
Omnivore Simple
Human Simple
 
Stomach Acidity
Carnivore Less than or equal to pH 1 with food in stomach
Herbivore pH 4 to 5 with food in stomach
Omnivore Less than or equal to pH 1 with food in stomach
Human pH 4 to 5 with food in stomach
 
Stomach Capacity
Carnivore 60% to 70% of total volume of digestive tract
Herbivore Less than 30% of total volume of digestive tract
Omnivore 60% to 70% of total volume of digestive tract
Human 21% to 27% of total volume of digestive tract
 
Length of Small Intestine
Carnivore 3 to 6 times body length
Herbivore 10 to more than 12 times body length
Omnivore 4 to 6 times body length
Human 10 to 11 times body length
 
Colon
Carnivore Simple, short and smooth
Herbivore Long, complex; may be sacculated
Omnivore Simple, short and smooth
Human Long, sacculated
 
Liver
Carnivore Can detoxify vitamin A
Herbivore Cannot detoxify vitamin A
Omnivore Can detoxify vitamin A
Human Cannot detoxify vitamin A
 
Kidney
Carnivore Extremely concentrated urine
Herbivore Moderately concentrated urine
Omnivore Extremely concentrated urine
Human Moderately concentrated urine
 
Nails
Carnivore Sharp claws
Herbivore Flattened nails or blunt hooves
Omnivore Sharp claws
Human Flattened nails

 

TO SEE A SUMMARY OF THE ABOVE CHARTS IN ONE PAGE, CLICK HERE.



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21 Comments

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I think the arguments presented here very interesting, however to use evolutionary theory and homology as a means to infer that humans are in fact meant to be herbivores seems like a specious argument.
One could just as easily theorize that humans were once carnivorous in some way as well but once they evolved opposing thumbs their need to chase their prey down and immobilize it, kill with bare hands and mouth, and tear the flesh off became of tens of millions of years much less important. This of ourselves is because they could use a spear, I imagine lots easier than chasing down a will boar on fool and lurching after it. And create knives fashioned from obsidian to scalp, and filet the beast. The end is result is that over evolutionary time the skeletal artifacts of became nothing more than vestigial remnants.
Survival of the fittest right? Adaptation, natural selection. If in fact evolutionary theory is true, then no one can possibly argue that eating flesh of any sort is wrong because the blind random chance of the evolutionary mechanism gave homo sapiens the ability to procure food of various types and in myriad ways.

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All valid comparative points, however. Humans started out vegetarian and moved in an omnivorous direction. Bears and Racoons started carnivorous and moved in an omnivorous direction. Based on their disparate starting points, of course Bears and Racoons have better meat eating capacity and poorer vegetarian capacity than Humans.

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"Humans started out vegetarian and moved in an omnivorous direction."

And your proof for that is what? If evolution is true we all started from precisely the same origin: primordial soup.

I believe you missed my point. I will state it as a couple of syllogisms.

If evolution is true
All living things evolved
Humans are living things
Therefore Human beings evolved

If something is random or chance driven it has no moral or intelligent cause
Evolution has no purpose/design (it is just random chance and mutation)
How living things evolve are a function of random chance/mutation
Therefore, a function of a living thing (e.g. eating meat) cannot not be argued on moral grounds or intellectual grounds since chance produced the function

Ultimately we can't argue as Vegans that eating meat is "wrong" if we also contend that evolution is true (as this author does). Since from an evolutionary standpoint there is no right or wrong just chance, therefore we can't even argue that humans are "designed" to be herbivores since evolution can't *design* anything. It is like assigning certain lego blocks to a numeric value and rolling a 20-sided dice to pick which blocks to put together. Would you call the resulting object a designed thing?


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I stumbled upon this page today, and I felt I should sign in and express my disagreement with the interpretations of the data. This article does a very good job of breaking down some of the differences between common herbivores and carnivores, and touches on what it is to be an omnivore. My disagreement is with the conclusions of the data and its interpretation with evolution.
The aspect of human evolution that is ignored in this article is that of intelligence. Once intelligence comes into play as an evolutionary factor then the possibility of intelligence solving a problem more quickly than evolution comes into play. What I mean by that is this. Bears hibernating was mentioned alot, so we can start with that. Bears tend to hibernate when their food sources are most scarce, and that is because that through the long period of time bears have been around all the bears who didn't hibernate and conserve energy when food ran low all died. Death is what drives evolution, not how well you do anything or digest this or that, but death. Now, for humans, if we were vegetarian, and there is far less plant matter available in the winter, one way we could have dealt with the problem of less plant material available would be to wait the thousands of generations it takes to kill off all of those people who couldn't hibernate. But with a long life, and intelligence, we gain the knowledge of the season to come, perhaps observing animals that put away caches of food for winter and stay awake, and so that is what we did instead of developing the ability to hibernate. That or we went south, or down into the valley, or whatever we did other than hibernate. Intelligence messed it all up, because it gave us an alternative to the massive death it takes to make an evolutionary change in a species. An interesting point also is that most industrialization and knowledge gain really got going in places that had a winter, but most old civilizations developed in places that had better weather than that. But thats for another arguement.
The adaptations required for intelligence itself affect things as well. For instance, ever wonder why we don't have a big bone ridge down the middle of our skull? Its because we have genetically weakened jaw muscles. A gorilla, which eats a majority of plant material, has a huge ridge down the middle of its skull, so that it can have all those muscles for chowing down on some plant material. That ridge is necessary for the strong muscles it needs to constantly chew food, because as a herbivore you need to chew alot of plant material to get by. Humans don't have that kind of chewing capacity, because we gave up those super strong jaw muscles in order to be able to keep expanding our brain case for a couple decades to fit all the knowledge and brain material we grow. With that intelligence increase we were able to cook food,hunt things, ferment stuff (woo hoo), and thereby eat a wider range of things without destroying our teeth, or if you don't want to jump into cooking, lets say "utilize a wider variety of food materials in different ways to gain nutrition". And to me that sounds like a good definition of omnivory. Every animal is a test of little tweeks and new things within the species. Humans, as a species, are brand new, and constantly expanding into new territories with new resources. Our intelligence is unlocking those resources faster than our bodies, through the process of genes and mutations, can keep up. Thats why only certain populations can eat dairy. I'm sick of people going on about how dairy is bad. I can eat dairy all day because I have the genes for it, and I don't care if you don't have them! The Inuit were the answer to a bad bad situation as well. Nature doesn't care if you die at 35 if you pop out your kids and raise them.
In fact, we have a tendency as a species to select for neotany, which basically means we are attracted to the characteristics of youth. Young girls don't dream of sex with some 85 year old man because his genes are so good they've lasted that long. The selection in both male and female selection has been towards adults who look like babies in most human societies. But I'm already realizing this is not organized enough to convince folks.
So let me say this. The rise of intelligence as an evolutionary factor is what this article is ignoring. I am not some religious nut talking about us being designed. I am talking about the fact that humans are intelligent and we are animals. To talk about a few omnivores that are/were predators and compare them to us who used to be mostly herbivores and are now omnivores is pointless because we took a different path. We took the path of developing our intelligence and are still paying the price for it. Other animals didn't do that as well as us, so it is difficult to make a comparison. Evolutionarily we are still "trying to decide what we are" for lack of a better term. We are undifferentiated omnivores. We have chosen to eat meat because we can, but we don't have all the adaptations of a carnivore that has been eating potentially the same meat source for 2 million plus years because that is not the selection force upon us.
A human with knowledge knows that there are not always plants about, but that there are almost always animals that can be eaten. Plants have much better chemical defenses against being eaten than animals. And as long as we know that we can eat something, then we will. And any vegetarian who is faced with the choice of feeding themselves and their offspring with the flesh of the formerly living, and chooses to not eat of the flesh and dies along with their children will ultimately not add as much to the human race genetically as myself and my kind. We know we will always choose to eat the flesh because we always have chosen to for as long as we were intelligent enough to be able to choose. Evolutionarily, limiting the range of potential foods is not the way to go. Unless you eat termites or ants or wood or something that is everywhere like that. And if you think that the world isn't going to reach the point where everyone is hungry, then don't worry, just keep eating only plants. But I for one will keep my options open. I am an omnivore by choice in an uncertain world.

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Responding to Unconvinced369. You are absolutely right that our intelligence changes everything. We have used our intelligence to create horrible environmental disasters, to create devastating high tech ways to cause mass destruction of other human beings, to create nutrition free "edible foodlike substances" and (as you are doing) to ignore the preponderance of evidence from the vast wealth of nutritional research over the past 40 years that shows direct connections between consumption of animal products and heart disease, cancer, diabetes and stroke. Diseases that are the main killers of Americans, but decrease in inverse ratio with the decrease of animal foods to where they are extremely rare in countries and among populations that eat little or no flesh, dairy or eggs.

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Steeve I agree with you 100%. Unconvinced369 It's about survival in the now, today, not back in the day. What is happening today is factory farming, pollution, pesticeds, antibiotics in food, GMO's, the list goes on....all in the name of profit and greed. So if it is about procuring the survival of humanity, than an organic vegan diet with superfoods and supplimitation would be the best way to not die from everything Steeve said, cancer, diabetes, heart disease etc...My proof is research, i have read a lot of books, medical journals, and watched documentaries...oh, and excercise. The best way to survive is too get up and move.

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There is nothing natural about our evolution in the last 10,000 years. Everything changed and NATURAL evolution stopped when farming was developed 10,000 years ago. It started with the herding of goats and the use of goat’s milk. We are the only species on earth that drinks another species milk. Furthermore we are the only species that drinks milk after nursing. Humans mimicked the large predators when they became smart enough to invent tools and weapons. Other than a turtle, name one animal a human can chase down and catch with their bare hands without weapons? Our own intelligence is killing us. We are the only species with artery disease (other than our pets we are now we are killing them too with our food). This article needs to be expanded to reveal that predators don't have clogged arteries. Tigers, lions, sharks, and all the other large predators don't have heart disease. A tiger will eat 100# of meat in one sitting and doesn't have heart disease. Their bodies are made to not absorb fat into their blood stream because they are true carnivores. 50% of all US deaths are related to heart disease, this is because our bodies are not designed to eat meat and the saturated fats from these meats are clogging our arteries. This is all amplified by the large portions we are trained to consume and all the antibiotics, steroids, growth hormones etc. that the animals we eat are fed. You are talking to a guy who spent his whole career as an Executive Chef. I have probably eaten worse than anyone you know. I used to drive 40 miles to get a great sausage and pepperoni pizza. But the scientific evidence is over whelming now. We stopped eating all meat except some seafood and cut out 99% of all dairy products and have lost 17# in 4 months. We haven’t even exercised yet.

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i thought that herbivores are animals that eat grasses, such as buffalo. while frugivores are more like primates such as chimps or bonobos, who eat mostly fruits and greens. and certainly it seems that humans do are not grass eaters. i think the author of this article is wanting to suggest that we are frugivores. which may very well be true. but let us not forget that both bonobos and chimps do occasionally eat meat.

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We are the only species with artery disease (other than our pets we are now we are killing them too with our food). This article needs to be expanded to reveal that predators don't have clogged arteries. Tigers, lions, sharks, and all the other large predators don't have heart disease. A tiger will eat 100# of meat in one sitting and doesn't have heart disease. Their bodies are made to not absorb fat into their blood stream because they are true carnivores. 50% of all US deaths are related to heart disease, this is because our bodies are not designed to eat meat and the saturated fats from these meats are clogging our arteries.

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Complete and absolute BS. There are no traditional societies that don't depend on meat for essential nutrients not contained in adequate quanitities in plant based diets. Plant based diets are ONLY possible in highly industrialized situtations.

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Although Unconvinced369 provides an interesting perspective on the inclusion of intelligence as rationale for the history of human diets that have tended to include animal protein, this argument hinges on the fact that it is an opportunistic survival behavior, adapted in the context of need to fulfill food shortage gaps. Intelligence may have very well led to this, but it fails to dismiss the reality of whether or not human diets are DESIGNED to include animal protein. Whether or not we are able to consume animal protein as part of our diet is obviously not the point of this article, human beings obviously continue to do so regardless. It simply points out by comparative analysis that our digestive system etc. has been adapted to a plant based diet more than one based on meat. The inclusion of the term herbivorous does not necessarily preclude any consumption of meat (chimps, gorillas primarily plant based). It does however demarcate meat as a less efficient food source in terms of compatibility with our evolution, and as mentioned by many previous commentators, is a significant contributor to the number one killer in America, Heart Disease

Based on this comparison, one sees that a plant based diet is more aligned with the realities of our anatomical evolution, regardless if humans have learned to incorporate meat into their diet. In this meat is more of a quick fix solution than one that is meant to become our primary nutritional input.

@tmgibs34 What do you mean by traditional societies? Societies untouched by the agricultural revolution? (virtually none) Hunter gatherers? (not salient to your argument of industrialized situations) The agricultural revolution was a convergent human social evolution, which allowed for the production of foodstuffs that allowed animal husbandry to flourish. This was by no means a physical evolutionary adaptation to include meat in the diet. Hunter-gather societies depended chiefly on a fruit, nut, root and herb diet, interspersed with meat (when available). All human consumption of meat today is by choice, habit or convenience in industrialized countries. All meat consumption in non-industrialized countries is a mix of theses along with specialized necessity based on the ecosystem in which they choose to live. We have no authority to argue what should or should not be eaten based on traditional societies, because traditional societies have still been shaped in the context of human social advancements in the last 10,000 years. Oh and biology 101 shows that "essential" nutrients that meat has are a result of the bio-accumulation effect from the animal's diet which includes the oh so tiresome argument brought out by meat-eaters about Omega-3 in meat, especially fish (Omega fatty acids in fish are a bio-accumulated source based on uptake of plankton, phytoplankton and algae either directly by directly or by those lower R-selected species in the food chain). All of the nutrients that come from meat come from plants, but become concentrated in herbivorous animals, which is why simpler food webs show that most carnivores do not make prey of other carnivores ( this is only in complex food webs)

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Although Unconvinced369 provides an interesting perspective on the inclusion of intelligence as rationale for the history of human diets that have tended to include animal protein, this argument hinges on the fact that it is an opportunistic survival behavior, adapted in the context of need to fulfill food shortage gaps. Intelligence may have very well led to this, but it fails to dismiss the reality of whether or not human diets are DESIGNED to include animal protein. Whether or not we are able to consume animal protein as part of our diet is obviously not the point of this article, human beings obviously continue to do so regardless. It simply points out by comparative analysis that our digestive system etc. has been adapted to a plant based diet more than one based on meat. The inclusion of the term herbivorous does not necessarily preclude any consumption of meat (chimps, gorillas primarily plant based). It does however demarcate meat as a less efficient food source in terms of compatibility with our evolution, and as mentioned by many previous commentators, is a significant contributor to the number one killer in America, Heart Disease

Based on this comparison, one sees that a plant based diet is more aligned with the realities of our anatomical evolution, regardless if humans have learned to incorporate meat into their diet. In this meat is more of a quick fix solution than one that is meant to become our primary nutritional input.

@tmgibs34 What do you mean by traditional societies? Societies untouched by the agricultural revolution? (virtually none) Hunter gatherers? (not salient to your argument of industrialized situations) The agricultural revolution was a convergent human social evolution, which allowed for the production of foodstuffs that allowed animal husbandry to flourish. This was by no means a physical evolutionary adaptation to include meat in the diet. Hunter-gather societies depended chiefly on a fruit, nut, root and herb diet, interspersed with meat (when available). All human consumption of meat today is by choice, habit or convenience in industrialized countries. All meat consumption in non-industrialized countries is a mix of theses along with specialized necessity based on the ecosystem in which they choose to live. We have no authority to argue what should or should not be eaten based on traditional societies, because traditional societies have still been shaped in the context of human social advancements in the last 10,000 years. Oh and biology 101 shows that "essential" nutrients that meat has are a result of the bio-accumulation effect from the animal's diet which includes the oh so tiresome argument brought out by meat-eaters about Omega-3 in meat, especially fish (Omega fatty acids in fish are a bio-accumulated source based on uptake of plankton, phytoplankton and algae either directly by directly or by those lower R-selected species in the food chain). All of the nutrients that come from meat come from plants, but become concentrated in herbivorous animals, which is why simpler food webs show that most carnivores do not make prey of other carnivores ( this is only in complex food webs)

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Although Unconvinced369 provides an interesting perspective on the inclusion of intelligence as rationale for the history of human diets that have tended to include animal protein, this argument hinges on the fact that it is an opportunistic survival behavior, adapted in the context of need to fulfill food shortage gaps. Intelligence may have very well led to this, but it fails to dismiss the reality of whether or not human diets are DESIGNED to include animal protein. Whether or not we are able to consume animal protein as part of our diet is obviously not the point of this article, human beings obviously continue to do so regardless. It simply points out by comparative analysis that our digestive system etc. has been adapted to a plant based diet more than one based on meat. The inclusion of the term herbivorous does not necessarily preclude any consumption of meat (chimps, gorillas primarily plant based). It does however demarcate meat as a less efficient food source in terms of compatibility with our evolution, and as mentioned by many previous commentators, is a significant contributor to the number one killer in America, Heart Disease

Based on this comparison, one sees that a plant based diet is more aligned with the realities of our anatomical evolution, regardless if humans have learned to incorporate meat into their diet. In this meat is more of a quick fix solution than one that is meant to become our primary nutritional input.

@tmgibs34 What do you mean by traditional societies? Societies untouched by the agricultural revolution? (virtually none) Hunter gatherers? (not salient to your argument of industrialized situations) The agricultural revolution was a convergent human social evolution, which allowed for the production of foodstuffs that allowed animal husbandry to flourish. This was by no means a physical evolutionary adaptation to include meat in the diet. Hunter-gather societies depended chiefly on a fruit, nut, root and herb diet, interspersed with meat (when available). All human consumption of meat today is by choice, habit or convenience in industrialized countries. All meat consumption in non-industrialized countries is a mix of theses along with specialized necessity based on the ecosystem in which they choose to live. We have no authority to argue what should or should not be eaten based on traditional societies, because traditional societies have still been shaped in the context of human social advancements in the last 10,000 years. Oh and biology 101 shows that "essential" nutrients that meat has are a result of the bio-accumulation effect from the animal's diet which includes the oh so tiresome argument brought out by meat-eaters about Omega-3 in meat, especially fish (Omega fatty acids in fish are a bio-accumulated source based on uptake of plankton, phytoplankton and algae either directly by directly or by those lower R-selected species in the food chain). All of the nutrients that come from meat come from plants, but become concentrated in herbivorous animals, which is why simpler food webs show that most carnivores do not make prey of other carnivores (this is only in complex food webs)

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Sorry for the three postings, page timeout and all that made refreshing the culprit here ;-)

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Very interesting facts, I think that more people should be aware of this.

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I'm sorry, but the logic behind the reasoning in this article is severely flawed. For a start, humans are primates and almost all primates are omnivores. The only primate I can think of offhand that is an herbivore is a gorilla. Chimpanzees hunt, kill, and eat other primates, and smaller primates are insectivores and frugivores. Primates have evolved brains and dextrous hands as weapons, and these allow them to work together in groups to hunt prey or use tools to extract insects from confined places. It's a different evolutionary strategy to animals of the carnivora order, such as lions and leopards, who need their mouths both to kill prey and to grip and tear meat because they don't have hands.

The author of the article seems to be focusing solely on the carnivora order to make its observations about omnivores and carnivores. Bears belong to the carnivora order, but not all bears are carnivores. Pandas are largely herbivorous, whereas polar bears are carnivorous, and other kinds of bear eat both meat and plant matter. Other omnivores from different orders include rats and mice and pigs.

Herbivores do not always have 'flattened nails or blunt hooves'. Rabbits and guinea pigs are herbivores, and they have claws similar to a dog's. Similarly, chimpanzees have nails and they are omnivores. Additionally, pure herbivores lack the vomiting reflex -- which humans share with other meat-eating animals such as cats and dogs. The vomit reflex evolved as a protective measure for when the animal ingests spoiled meat.

Also, several groups of people, most notably the Inuits, eat a largely carnivorous diet (and mostly raw). If humans were not adapted to this diet, Inuit people would be malnourished, have a severely shortened lifespan, and probably be unable to breed, and I have never seen any evidence presented to this effect. Much of the modern Western diet is supported by grains, i.e. processed food that is inedible in its natural unprocessed form. Without cooking, the only realistic sources of food for humans would be fruits, tubers, and raw meat. It would be extremely difficult not to become malnourished as a wild animal on this diet if no meat was available.

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@turdburger Do you have more evidence than your statement "almost all primates are omnivores." or are you guessing?
I did a tertiary search and found that you can now add:
Bonobos
Gelada baboons
Howler monkeys - Leaf eaters
black-and-white colobuses - Leaf eaters
sportive lemurs - Leaf eaters
Mantled guereza
Marmosets - gum eaters
Gelada - primarily feeds on grass

...to your herbivore list with Gorillas.

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Bonobos have been observed hunting and eating meat (and also other bonobos) in the wild. It is not known how frequently they do this, simply because they have not been studied enough. Marmosets eat a variety of food from both plant and animal sources, and howler monkeys, while they mainly specialise in leaves, have been observed eating eggs. Geladas (which have been included twice in the list) despite being mainly grazers will eat insects if they are available.

While people like to try to classify things tidily into categories, there are not that many species who have evolved to specialise in only animal or plant sources of food, and rather more who fall somewhere between these two extremes. The argument in the original post uses data that doesn't really mean anything in order to impart an appearance of scientific credulity. I've seen the same argument on dog food advertising to claim that dogs and wolves are carnivores (which technically they aren't as they are observed to eat plant material in the wild). The lines dividing them are not that clear.

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Everyone on here trying to talk about the history of man's diet needs to do some serious fact checking! For thousands of years around the world the biggest component of our diet as been starch based PLANTS! Rice in Asia, barley in the Middle East, Wheat in Egypt, millet in Africa, maize in the Americas ect.. The only people who ate meat were royalty and they were just as diseased as the rest of you omnivores, they've found hardened arteries in most of the mummies in Egypt because they were wealthy and powerful enough to have a meat based diet! If you want to be really strong and healthy take a page out of the history books roman legionnaires, gladiators, the infantry men of Genghis Khan, Attila the Hun, and Alexander the Great all lived and thrived on a starch based diet.

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Hello,
I think your article is excellent and feel it proves via one method of analysis that humans are not carnivores. However, I do not feel it proves we are meant to consume a vegan diet. In other words, it still does not prove we are meant for no animal food at all, just that we are not necessarily meant to consume animal foods in the way carnivores do, and also that much of our animal-related nutrient should come from the types of animals that do no require the anatomical features of say a lion to consume them. My point is this- one would be hard-pressed to find a logical, clinically oriented physician recommending a vegan diet, who does not also recommend a B-12 supplement. Even T. Colin Campbell takes B-12. Why? We need it and can't get it from a vegan diet. Some vegans argue that we would get it all if our food wasn't sterile and still ate the bugs that came along with food when procured in nature. What is a bug? An animal. Does eating a bug require massive temporalis muscles, etc? No. The second part of my argument is that even though we are not designed to eat meat the way a carnivore does, it does not prove we are designed to NOT eat meat, just to NOT eat meat that way. In essence, we are designed to eat bugs and....cooked meat. Humans are adapted to eating cooked food. We do not share exact anatomical features of an omnivore, a carnivore or an herbivore in the wild, we are completely unique. Why? Because we are the ONLY animals on the planet adapted to eating cooked foods. Our need to consume B-12 proves our need to consume foods that contain it, ie animal foods. Our lack of exact correlation to omnivores, carnivores and herbivores proves we are not exactly like any of them. Our closeness in design to omnivores and herbivores proves we are designed for that type of food, but not ONLY that type of food.

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Isn't it funny how you can use information to get whatever results you like. The website www.second-opinions.co.uk/carn_herb_comparison4.html also uses anatomical features to compare man, dog and sheep to conclude that we are carnivores and shouldn't eat any veggies! But when you read down the list, some of the evidence includes that we don't need to chew our food and that it is impossible to survive without animal protein. No wonder they had putrefactive bacteria and small firm faeces (sorry, have to look at that site to know what i am talking about)
I like the conclusions on this site much better because they promote vegetarianism, but it would be great if there was a link to some of the raw data- like the actual lengths of the intestines of different animals, their stomach pH etc.
Nearly always when I hear about evolution it is from the past to the present, but doesn't consider the future. Even if humans were meat eaters in the past or present, we are still in the process of evolution. Just look around and compare the "meat head" mentality and intelligence level with the radiance of people who eat a balanced plant based diet with plenty of raw foods. Which direction to we want to be heading in? I think the yogis were onto something when they categorized foods according to their effect on the mind.