Are humans omnivores or herbivores?

Most humans are behavioral omnivores, but are we naturally so? Are we fit for eating meat and cheese as much as fruits and vegetables? Or are humans natural herbivores?

Definitions

 * Omnivores are animals anatomically and physiologically adapted to eating both plant and animal matter.
 * Herbivores are animals anatomically and physiologically adapted to eating plant material as the main component of their diet.

Pro

 * Humans gain significant nutrition and energy from meat.
 * Humans break down (and decontaminate) meat using fire (cooking) because their stomach cannot do this properly. They also cut meat using tools (knives) because their mostly-flat teeth cannot do this efficiently. The vast majority of humans would never tolerate raw meat but they came up with a clever hack to eat meat despite their body not being designed for it.
 * Humans do sometimes eat raw meat, as evidenced by dishes like sushi and steak tartare, to name a few
 * Sushi is only safe for saltwater fish as the fresh/salt water barrier renders the human body lethal for ocean based bacteria and parasites. Steak tartar is heavily processed, which does not counter the previous example.
 * This objection fails to account for the fact that humans evolved alongside cooking and that our need to cook food before eating it is completely natural for us. Eating cooked food for us is as natural as birds building nests. Our body is designed to ingest cooked food.
 * Humans are not evolutionarily passed down the ability to cook food.
 * Cooking is a learned behavior, passed down culturally
 * Passing down cultural knowledge is not relevant to the Definitions section which states "anatomically and physiologically adapted".
 * Not germane to the premise that humans gain significant nutrition and energy from meat.
 * Not germane to nutrition from cooked meat, but is germane to nutrition from raw meat, which is relevant to structure and function (anatomy and physiology).
 * The human body lacks the capacity to regulate the iron in red meat, and is associated with a higher risk of colorectal cancer, while, anatomical carnivores/omnivores do not develop such issues.
 * This whole point is completely redundant for both arguments, as for cancer as many plants when consumed repeatedly like meat also contain cancer causing agents ( celery, rubarb, many edible mushrooms, Bracken fern(Tea / soup) and can generate higher risk of cancer too the main issue is the levels of intake in modern society where we consume to much of one thing is the issue rather than the consumption itself, in addition the life span of most carnivores is less than then general age most people start to pass away from cancer, so that's why carnivores do not suffer form cancer as they are long gone before this would effect them.  The point with iron is utterly wrong as humans can regulate iron through the point at absorption, utilisation and recycling(the liver plays a key role in this process) its just red meat contains a lot more iron than we can absorb so most is excreted out as excess iron is not controlled by humans, note is also the case for most other animals too.
 * Cancer, especially colorectal cancer has a very well studied pattern of progression, with accumulation of mutations and progressive worsening of dysplasia, a process that takes time and thus a disease that is associated with old age. This makes it not relevant for evolution purposes. In most of humanity’s existence span, getting enough calories, not starving or being killed by predators were the definitin factors for survival, not cancer.
 * Consumption of meat being related to cancer is a myth. Yes, meat contains some carcinogens, but the benefits of eating meat far outweigh the risks, which you should only worry about if you eat excessive amounts of meat.
 * The benefits of eating cooked meat might also be a myth, since it is known to be less healthy than a proper vegan diet or vegetarian diet. In any case, cooked meat isn't relevant to physical structure and function since humans evolved to essentially our present state before cooking meat.
 * This objection contradicts itself. The concession, meat contains carcinogens (cancer-causing agents), contradicts and disproves the premise of meat consumption being related to cancer as a myth.
 * Behavior only tells us what we already know, and we are all acutely aware that meat eating is a common practice. But so is traveling via airplane, and the fact that so many of us do so, doesn't mean we have specific physiological adaptations towards this behavior.
 * Humans have a trophic level of 2.21 (same as anchovy and pigs). Anchovy subsist primarily on zooplankton, and pigs are omnivores. Animals with such a trophic level can subsist on a widely varied diet.
 * Level 2 of the trophic level index includes herbivores, level 3 or higher includes carnivores. A trophic level of 2.21 doesn't imply that humans are omnivores.
 * Our closest evolutionary relatives, chimpanzees and bonobos, are omnivores. As their biology most closely resembles ours, it's more likely that humans are omnivores too.
 * Only a very small portion of the diet of chimpanzees and bonobos comes from meat, they do not appear to have specific physiological adaptations to eating meat. In keeping with that, insectivores are often thought of as distinct from common carnivores, even though insects are still in the kingdom of animalia.
 * Carnivores have also been reported eating plants. They are carnivores nonetheless. The taxonomic classification of omnivore/herbivore/carnivore, is something that biologists have a tendency to make based exclusively on behavior without placing that much weight on anatomy.
 * Humans wean earlier than herbivores, a pattern that matches that of carnivores. Chimpanzees (our closest evolutionary cousin) wean their young on average at around 5 years old and orangutans (the apes closest to our body weight) wean on average at 7.7 years old, which almost no human society does. Meanwhile, the average human weaning age is 2 to 4 years old, which is considerably shorter than in chimpanzees and orangutans, even accounting for cultural differences and individual preferences.
 * Clever human behaviors like weaning as early as is practicable don't speak clearly of structure and function.
 * Bonobos are our closest relatives, not chimpanzees. Human weaning varies by culture which has been determined more by the outcomes of wars than by bodily structure and function.
 * Many herbivores wean earlier than humans, such as cattle and sheep.
 * Herbivores, such as cattle and sheep, have additional anatomical structures that enable digestion of a strictly vegetarian diet.
 * Herbivores having additional anatomical structures has no clear (un-implied) relevance, pro nor con, to the timing of weaning being meaningful.
 * Cattle and sheep have been domesticated by humans to wean earlier than they used to because separating them is profitable and often times so is their milk.
 * Humans wean before herbivores because we adapted to drinking milk from domestic animals. Originally drinking milk from other species made us sick, this remains in some people and is known as lactose intolerance.
 * Lactose intolerance is not due to animal milk. This fact happens due to the deficiency of the lactase enzyme. If milk is consumed regularly, the body will produce the necessary lactose again (depending on the case).
 * People can be intolerant as a baby without ever having taken animal milk.
 * Humans, like many predators, have forward-facing eyes rather than eyes on the side of our head as prey would. This would imply that we are designed to hunt and eat other species.
 * Forward facing eyes is related to how cluttered your environment is, an open environment leads to side facing eyes. Due to humans living in forests we needed forward facing eyes, which are correlated with a more cluttered environment.
 * Many mammals live in the forest without this adaptation.
 * The validity of one animal developing forward-facing eyes to deal with clutter (such as due to their niche or their habit of brachiation) doesn't necessitate that every animal in every niche with every locomotive modality in cluttered environment must do likewise.
 * Many predators don't have forward-facing eyes, and many herbivores have forward-facing eyes.
 * No land predator (except Dinosaurs [extinct reptile]) have side head eye. Only know non extinct predators with side eye are whales & sharks (water based animal). Also a substantial number of herbivores likely have side-facing eyes with few exceptions.
 * The exceptions stated in the objection invalidate the objection, because the the exceptions cannot be disregarded merely due to being less common or to being extinct.
 * Humans descend from tree-dwelling animals, that needed precise forward-looking binocular vision to avoid falling when leaping and moving around.
 * The vast majority of humans practice an omnivorous diet and have been doing so for hundreds of thousands of years, and many live long, healthy lives.
 * This debate is about the anatomy and physiology of humans, not about what they have been doing through will power. The same way, if all humans on the planet decided today to start eating exclusively vegetables, this would not make them more herbivores. Only their physiology would answer this question, not the habits they acquired out of sheer willpower. Humans decided (willpower) to burn meat using a tool (fire) in order to digest what they could not otherwise digest. Fire, an external pre-processing tool, became a hack giving them the ability to eat what their stomach could not otherwise break down due to weak hydrochloric acid. A group of humans suddenly deciding to live in the waters would not instantly become water creatures until they start developing fins through thousands of years of evolution. Therefore, physiology is the only element that should be considered in this question.
 * Humans who eat a vegetarian or vegan diet tend to live longer and are less prone to various diseases and conditions.
 * The first half of this statement is compliantly wrong as historically before modern transportation and the current availability of food people ate what was available to us which to 99.9% of people was a combination of both plant and animal. It was impossible for vegans to exist in the world as the plants in most regions will not provide all the different nutrients we need to be healthy and survive many vegans in current modern day take supplements in order to remain healthy these did not exist before modern times. The main area where historical vegans existed were limited parts of china and india where there was enough plant species that provided the nutritional variety needed to support a vegan diet.
 * This statement is false. As the simplest example, rice and lentils alone provide a nearly complete nutrient suite. It is both reasonable, and supported by various aboriginal studies, that when locally available nuts, roots, vegetables, grains, and fruits are considered, it is entirely possible to subsist, particularly in warmer and more plentiful regions of the world.
 * This does not describe the physiology of humans but only their will. This logic would mean that if all humans decide to eat exclusively meat, they would be carnivores, and if they decide to eat exclusively vegetables, they are now herbivores.
 * For the most part, "omnivore", "carnivore" and "herbivore" have historically been defined by behavioural measures. Numerous species that have previously been defined as herbivores, including hippopotamus, sheeps and cattle,  and many others , have been shown through behavioral observation, or through fecal and stomach content analysis (both the result of behavior) to deliberately consume meat and carrion, even predating small animals. These findings cause scientists to rethink the categorization from herbivore to omnivore, or at the very least "partially omnivorous". If other species are defined by their behavioral diet, then so must humans.
 * This entire line of logic is irrelevant to this wiki page. If behavior was allowed to determine the answer, then the answer would be an entirely foregone conclusion obviating the existence of the page because the only relevant Objection to herbivore diagnosis would be simply "Humans eat meat". This page is about being "anatomically and physiologically adapted" to eating meat.
 * Omnivorous behavior in humans is a cultural universal (with few exceptions like Jains, Amish and Hindus). Such cultural universals can be attributed to our genetics, and in turn to our physiology.
 * Exceptions cannot be disregarded. Such cultural pseudo-universals can be explained easily by big-brain genetics whereas this wiki is about the structure and function of eating meat. For example, it could be true that any herbivorous species which isn't a strict herbivore, upon gaining sentience, would use fire to unlock nutrition from meat, and therefore habitually misidentify themselves as omnivores adapted physiologically to meat eating, and make a wiki about it.
 * Omnivorous behavior in humans should be considered cultural or technological, not physiological. Basic human physiology is NOT well equipped to eat or obtain meat (other than perhaps insects or grubs), even though humans are able to eat/obtain meat once they develop tools/technologies towards this (which could take generations to reliably develop). Creating and drinking alcohol is also very widespread in human cultures, but this does not mean that humans are genetically or physiologically designed to do so - alcohol consumption is a cultural and technological development, and not due to a basic physiological need to consume alcohol.
 * A number of non-human species may deliberately consume psychoactive substances, including mushrooms like amanita muscaria and rotten fruit containing alcohol.
 * Humans need micronutrients like vitamin K2, taurine, creatine, DHA, carnitine and carnosine within our diet which are more difficult to obtain from plant based foods. The bioavailability of nutrients in meat makes it also much easier for the human body to obtain them than from plant-based foods.
 * Those nutrients are not essential for human health.
 * Don't forget about B12.
 * The human need for B12 is low, and most primates in the wild are able to get this from supplementing a mostly herbivorous or frugivorous diet with insects (e.g. termites, ants, etc.).
 * The human need for B12 is low, and most primates in the wild are able to get this from supplementing a mostly herbivorous or frugivorous diet with insects (e.g. termites, ants, etc.).
 * The human need for B12 is low, and most primates in the wild are able to get this from supplementing a mostly herbivorous or frugivorous diet with insects (e.g. termites, ants, etc.).
 * B12 is produced by a bacteria found in soil. Before large scale farming and pesticides, humans and animals got their B12 from plants grown in soil. However, due to soil desertification and mineral depletion, B12 is no longer found in most of the soil that we grow our food in. This means that even people who eat meat should be taking a supplement, as it is now one of the most common deficiencies.
 * Yes they are.
 * If humans are not omnivores, why are we attracted to the physical properties of meat?
 * Largely speaking, humans are not attracted to the physical properties of meat. Just the opposite. Almost any human is repulsed by attempting to eat almost any kind of raw meat as it is found in nature. Humans are attracted to only the most plant-like meat, such as cooked meat, sushi, and steak tar-tar, which is to say, grind-able with molars.
 * To feel attracted is not an argument. It is likely that eating meat started largely due to the scarcity of calories from any source, plant or animal.
 * A human baby is not attracted to kill a small animal when shown one. On the other hand, the desire to hunt is so deeply embedded in a kitten that they will chase mice instantly.
 * Being omnivores or carnivores does not require being hunters of the type that overwhelm prey in an instant. Humans have poor ability to hear or smell prey (as opposed to predators), but exceptional ability to detect if meat is rotting by smelling it, and very intense gag reflexes when trying to eat it, which fits an opportunistic scavenger (as opposed to an outright carrion feeder) and is thus in line with humans being omnivorous, even before persistence hunting by endurance running or even hunting with tools developed. With regards to persistence hunting, humans experience the sunk cost fallacy, which keeps them fixated on their current prey individual specifically (in line with persistence hunting), whereas most predators use their overwhelming physical prowess and switch the specific individual they prey on until they get lucky.
 * Human babies (even though humans are commonly called hunter-gatherers) are not keen to search for, collect and gather things, either; as a matter of fact, human babies are virtually helpless (in comparison to most mammals), and have virtually no inborn instincts of complex behaviours (in comparison to most mammals). This is illustrated with overwhelming clarity when comparing how typical (of that kind of animal) the behaviour of any non-human mammal will be, even when it grew up isolated from it's species; this is true even for primates, who often adapt to live with their kind with relative ease. However, humans who grew up in isolation from other humans (feral children) will to a large degree continue to behave like the non-human animals they grew up with for their entire lifetime. Humans who grow up in total isolation (not even the company of animals like feral children) die with almost absolute certainty because they don't know what to eat, and more importantly, what not to eat; that is to say: even to be herbivores, humans need to mimic and learn from their kind for the first few years, or they will die. This shows that human instincts and human behaviour are learned for the most part (mostly nurture, little nature). Once this is understood, it comes at no surprise that humans who grew up in a hunting culture frequently develop a strong instinct and intense desire to hunt as well. Given that humans have been hunting for millennia, given that hunting/fishing is a normal, common activity in all primitive cultures and remained common in almost all developed cultures (except for a few places with religious or legal restrictions) until modern vegetarian/vegan diets, and given that humans depend on mimicking and learning from their kind to develop into behavioural humans (as opposed to merely being physically human but behaving like, eg, a dog, as is seen in feral children), this renders the argument void that "kittens have a desire to hunt, but human babies don't".
 * Human babies do in fact exhibit gathering instincts which explains the wide phenomena of them seeking and consuming shiny objects such as marbles and coins. Said objects resemble commonly gathered food like berries. While it’s true that humans are helpless our first few years of life, we’ve evolved to subsist on our mother’s milk until we reach an age where we can stand up straight and thus gain the ability to gather fruit, nuts and seeds. This is a similar natural progression to our relative primates. Contrast this with children being completely reliant on their parents to cook meat for them, a trait that no other omnivore presents.

Con

 * If humans were meant to eat meat, why would nature dictate that we have to cook or cure to make it safe for consumption?
 * Cooking meat has far more to do with our brains than our inability to eat raw meat. Which we can do, in fact. Cooking meat before eating it releases far more calories and nutrients than raw meat, which allowed our ancestors to evolve larger and more complex brains.
 * What really allowed our brains to evolve to be larger was the cooking and consumption of roots. As seen by many hunter gatherer groups eating tubers and roots that are calorically dense, but can only be digested when cooked.
 * there is no individual factor with this that is correct as the combination of both the higher level of nutrition from cooked meat needed for brain development combined with the increased energy cooked starchy roots allowed brain development as neither would work with out the other as having the nutrients from meet to have a larger brain would be a disadvantage if you didn't consume enough calories to and likewise having the calories but not having the components needed to generate and maintain a larger brain mass would end just as badly.
 * The formulation... *nutrients* (potentially with calories being irrelevant) from meat *for* brain development (potentially without aiding higher level of energy) versus *calories* (potentially with nutrients being irrelevant) from roots *for* higher level of energy (potentially without aiding brain development) ...while aesthetically compelling, isn't clearly the correct formulation.
 * Humans can and actually do consume raw meat. However, cooking has a huge advantage as it increases food use efficiency. Cooking makes the nutrients more accessible, which allowed our ancestors to spend less time foraging, chewing and digesting. Thus, humans developed a smaller, more efficient digestive tract, which combined with the more nutritionally accessible food and consequent energy surplus, enabled larger brain growth. While humans can still digest raw meat, our digestive tracts is now adapted to digesting cooked food.
 * No humans can and actually do consume raw meat in a meaningful quantity.
 * Only anatomical herbivores develop atherosclerosis when exposed to high levels of saturated fat and cholesterol. Animals with sufficient physiological adaptations to eat meat do not share this trait. We can cook vegetables and eat them without negative effects on our health, the fact that there are well documented negatives effects from meat consumption (which persist even after cooking) mean it is just not what's best for our anatomy.
 * many meats are fine for consumption and the level of negative effects are similar levels to a lot of plants that also contain there own series of negative effects, however these effects only impact people after the main active/ reproductive life of people while during them meat is a massive boon especially for pregnant women where eating cooked meat helps massively with a child's development due to the sheer amount of essential required for brain and neuron development. The fact that it has a negative impact later on after the reproductive period of a persons life is inconsequential since it will not hinder humans as a species to persist, while this sounds cold and cruel these types of trades offs are common in nature.
 * Effects after the reproductive period of life cannot be disregarded, because humans and all our close relatives are highly social animals who form group-wise bonds and rely upon post-reproductive elders for significant survival advantages. The massive nutritional boon (such as for pregnant women) only applies to cooked meat, the relevance of which is under question, and regardless a nutritional boon doesn't contradict the main argument about atherosclerosis from saturated fat and cholesterol not being a meat-eater kind of trait.
 * Animal products contain components which cause many prevalent chronic diseases, including cholesterol, which causes the inflammation of the arteries and can lead to atherosclerosis, cardiovascular disease and strokes.
 * Being an omnivore allows for a quantity (and variety) of animal product consumption that will not inherently lead to chronic disease.
 * In the United States, we consume meat in almost every meal. Consuming this amount of cholesterol, sodium, and fat can, and will lead to a chronic disease. which is curable through a vegan diet.
 * Resolving an extreme with another extreme is not necessarily the best solution. That is, there is another option to resolving meat as it is consumed "in almost every meal" other than completely cutting it out: moderation.

Pro

 * Human jaws move sideways like other herbivores while being equipped with flat molars. The combination of the two is a mill to grind seeds and chew vegetables. No animal eating meat other than for survival into regions that lack vegetables has flat molars with a side-moving jaw. Animals eating meat in normal circumstances have sharp molars and a fixed jaw, forming scissors that can cut bones (as opposed to broken and flat scissors).
 * we have biting/tearing/ripping incisors and canines (like carnivores) and chewing molars (like herbivores). Animals with such diverse teeth are usually omnivores.
 * Canines like ours have been structurally tied to gaining access to nutrients locked behind a woody surface, like many nuts and their protective layer. There is no evidence for their use in the act of hunting.
 * Other herbivores that are closely related to us (like Gorillas) have much larger canines while not eating meat
 * Gorillas are also omnivores along with most primates as all eat the flesh on another animal regularly even if those tend to be insects. Note gorillas like their termites and even developed there own tools to help catch and eat them.
 * Ants and termites make up an absolutely minuscule amount of a gorilla's diet. If that's all it takes to be termed omnivore, then the definitions themselves aren't useful... and of course humans can make up dubious or self-serving definitions.
 * Some of our closest evolutionary cousins (chimpanzees, bonobos, gibbons, gorillas and orangutans) are herbivores.
 * Chimpanzees are the closest living relatives to humans, sharing about 98.6% of our DNA. Chimpanzees are not strictly herbivores; they are omnivores. Their diet consists of a variety of foods, including fruits, leaves, seeds, nuts, insects, and sometimes small mammals. While plant-based foods, such as fruits and leaves, make up a significant portion of their diet, chimpanzees also supplement their nutrition with animal protein from insects and occasionally hunt and consume small mammals.
 * Bonobos are our closest relative, not chimpanzees. Chimpanzees eat the most meat of all our relatives, which is still a tiny amount. Bonobos eat the least aside from gorillas.
 * You would have to prove that they aren't simply a herbivore that will sometimes supplement their diet with animal protein when a promising opportunity presents itself, as seen with horses. Given this information, the proportion of animal protein in their diet would have to rise above "occasionally consuming small mammals" to move beyond the herbivore classification.
 * Deers, chimps and bonobos frequently eat termites, ants and other insects, which are still meat.
 * Dietary classes such as herbivore, omnivore, insectivore, etc. refer to an animal's primary or predominant diet. An herbivore (such as a deer) is still an herbivore even if it occasionally eats an insect or bird. A carnivore (such as a cat) is still a carnivore even if it occasionally eats plants.
 * Deers and chimps also eat ants and termites but are still considered to be herbivores. This is merely opportunistic feeding. The bulk diet of a deer is plant material, and the bulk material of a healthy human diet is plant material.
 * Chimps have been documented hunting and eating small mammals. Besides, the source states omnivores as opportunistic feeders.
 * The argument stated "some". Chimpanzees eat the most meat (still a tiny amount) and aren't the closest relative, so the cherry-picked example of chimpanzee hunting doesn't logically undo the argument to which it objects.
 * Humans lack claws, sharp teeth or other natural weapons.
 * Our natural weapon is our brain, which can and is used to make other weapons and strategies.
 * Our brain's complexity, and subsequent development of novel behaviors, has no bearing on whether our bodies are intended to consume a herbivorous or mixed diet. The proposed period of time since tool use is insufficient to allow for our physiology to evolve towards meat consumption, and our natural tools clearly suggest that we didn't rely on predation prior to a meaningful extent prior to that point.
 * Many other species also lack these weapons that eat meat like a lot of predatory fish where the only thing that have is being bigger than their lunch, which we also have when you compare us to a chicken. also we have one major advantage to common animals eaten as prey and that's endurance running as people that are still hunter gathers are able to keep running/ chase after a target until the animal collapses from exhaustion.
 * The argument stated "or other natural weapons". A toothless predatory fish's ability to swallow another smaller fish whole *is* their natural weapon which constrains, constricts, and suffocates while minimizing its own internal damage. Humans have no such weaponry.
 * An average human adult has a 22 feet long intestinal tract, small and long combined. The chest size of an adult is about 26 inches. The ratio is therefore 10.15. Other herbivores are also known to have an intestinal tract of 10 to 12 times their chest length.
 * Human gut length is much shorter than in other species because of the evolution of cooking. As cooking (including meat) made food more nutritionally accessible, there was no longer need for evolutionary expensive excess gut tissue.
 * Cooking hasn't been around long enough to alter human gut length significantly, so if humans have a herbivore gut length/ratio, then we evolved to have it.
 * This would only be an explanation of humans (and herbivores) had shorter, not longer, intestinal tracts. Carnivores have an intestine to chest ratio of about 3-6 while humans and herbivores generally have 10-12
 * The terms herbivore, omnivore, and carnivore are science-like, but have no clear scientific system behind them. Given that humans created the terms, potentially with deep psychological bias regarding fearing and idolizing predators due to being herbivorous troop animals, if the terms are indeed biased, that suggests support that humans are herbivores. We do see bias in two ways. (1) A species can eat a higher percent of vegetation while being called carnivore than vice-versa for being called herbivore. In other words, carnivore is lax while herbivore is very strict, just enough to allow humans into the omnivore club. If herbivore were to reflect the same percentage as carnivore, all great apes would be undeniably herbivores anatomically and physiologically, hence the lopsided definitions, hence the potential for this discussion to even exist. (2) We also see bias in terms like "mostly herbivorous" and occasionally "omnivorous" applied to even gorillas for example for eating some ants wheres we don't say "primarily carnivorous" for animals who eat a similarly minuscule amount of plant material (catnip and zoopharmacognosy).

Con

 * Unlike herbivores, humans lack a specialized compartment (such as a large cecum) for the fermentation of plant material, indicating a different digestive strategy.
 * This fails to account for the relatively easy digestion of fruits, many vegetables, many leaves (such as lettuce), and nuts. Instead, we have an intestinal tract of 10.15 times our chest length, aka a relatively long digestion process, which is common in herbivores.
 * The absence of a ruminant digestive system, common in herbivores, further underscores that humans are not specialized for processing large quantities of plant material.
 * Argument redundant with above.
 * The ability of humans to thrive on various diets, including plant-based, omnivorous, or carnivorous, highlights our adaptability and contradicts the strict herbivore categorization.
 * The ability of humans to bypass natural processes and limitations, including those of our own body, means we must look to the actual physiology of our bodies, not our behaviors. The entire purpose of this discussion is to determine what meal composition is biologically optimal.
 * Our evolutionary history as opportunistic omnivores is evident in our ancestors' adaptation to diverse diets, including both plant and animal sources.
 * We have much speculation but no hard data about any such history. By comparison, the biology we currently possess, and that of our "cousin" species, is a considerably more testable and reliable standard.
 * Humans can't derive energy from cellulose due to a reduced gut. All other herbivores and plant-based omnivores (e.g. great apes, pigs) can actually do this.
 * Dietary fibers (which include insoluble fibers like "cellulose") are undigested carbs that seem more like a necessity for humans and other herbivores in regards to many aspects of health. Herbivores do not create any enzyme that breaks down cellulose. Instead, they eat food that contains these enzymes.
 * There are different subcategories of herbivores (i.e, folivores eat foliage, frugivores eat fruits). Frugivores often are monogastic rather than ruminant animals. Even rumiant have a very limited ability to digest celluose, however they make it because they spend much of their day ruminating.
 * Humans basically have traits of frugivores but are unique in our ability to digest starches more efficiently, a typical starch-eating animal not only eats it raw but has much less salivary amylase than a human; humans secrete 3 times more salivary amylase than the other great apes, which allows from up to 40% of the breaking down of starch into glucose to happen in the mouth and the rest to be handled by the pancreas. This is a specific adaptation to the consumption of a plant based energy source.
 * Humans require vitamin B12 in their diet, unlike herbivores which can make their own in their colon with the help of bacteria.
 * Humans also create vitamin B12 in their colon with the help of bacteria. However, no animal can assimilate their own B12, they must get it from outside of their body. Most animals lick bacteria-rich soils. Humans can cultivate their own vegetables and make sure they grow in rich soil. If they don't wash the vegetables with chlorinated water, B12 will be found on it.
 * Humans cannot get the recommended amounts of vitamin B12 without meat in their diets. Herbivorous animals have both different gut flora, which allow for the production of vitamin B12 and have fore gut fermentation, meaning they can absorb it. Human gut fermentation takes place in the colon, at which point the absorption level is insignificant. All non-herbivorous animals almost exclusively get their vitamin B12 intake from eating other organisms.
 * Humans can get enough B12 without meat, the problem today is that we live in a much cleaner environment. B12 isn't created by animals, it's created by bacteria in dirt. And in the past we got significant amounts of B12 from water that wasn't entirely clean, plants that still had traces from dirt on them, and by the dirt and bacteria that could be found on our hands before we started cleaning them.
 * this statement is massively incorrect as the bacteria that produce b12 is from decomposition / digestion and the only water sources that would contain enough B12 to sustain a person would be highly contaminated with raw feces and heavily decayed material with masses of this bacteria present so drinking that water would be a death sentence from the sheer number of illnesses you would catch from drinking it.
 * The objection addresses water sources of B12, but the body of the statement remains, that B12 was available in the natural environment without meat.
 * Only ruminant herbivores can produce and assimilate their own B12 due to having multiple chambers in their stomach. All other herbivores (the vast majority) are no different than humans in this regard since the sole purpose of a single-chamber stomach is to break down food as it is ingested before quickly transitioning to the intestines for assimilation. The production of B12 in the colon (all non-ruminant animals, including humans) is only a by-product of a rich microbiome. Such microbiome would normally also be found in the soils if our farming industry was allowing natural bacteria to exist (e.g. not killing them with products and processes). In a rich soil that was kept out of human interference, bacteria generates B12 which then travels to the vegetables through their roots.
 * Cattle can’t get B12 either and they are often touted as being the strictest herbivores of all. They are often given B12 supplements and that's the primary reason why skeletal muscle tissue found in supermarkets contains ample levels of B12. B12 is abundant in carnivorous because many of them consume the liver and the contents of the digestive tracts of their preys, which is full of B12 bacteria.
 * If cattle could not produce their own B12 (through different gut flora and fore gut fermentation) they would die; however, free ranging cattle do not die. Hence, the B12-supplementation-to-supermarket-meat is nonsensical.
 * They don't die because they're free range and absorbing B12 from the earth. The extremely large majority percentage of livestock live miserable lives locked up and therefore have no access to this, hence B12 supplementation-to-supermarket-meat.
 * This doesn't help the point at all, instead only emphasizing that it isn't relevant data to this discussion.
 * This objection lacks specifics about why it doesn't help the point or why it's irrelevant. This wiki is for logical objections, not for vague commentary, so to summarize the point briefly: Modern wild cattle and ancient wild cattle and ancient humans (humans at the time of anatomical evolution) all had B12 available from natural non-meat sources. Modern captive cattle and modern humans both need B12 supplements in the form of B12 pills or B12 supplements in the form of meat from cattle who were wild or took B12 pills.
 * Humans selectively absorb heme iron in the small intestine with specialized receptors. No herbivore does this.
 * Heme iron has been shown to cause heart diseases and alzheimer.
 * Heme iron causing Alzheimer's being a bad thing doesn't negate all potential good aspects of heme iron and doesn't speak to specialized receptors for accomplishing its absorption.
 * All omnivores are opportunistic meat eaters, human society developed a way to allow humans to have constant meat intake every day of their lives, which is the true cause of those diseases. Omnivore is not carnivore.
 * Heme iron is present in plants as well- this is why foods such as the Impossible Burger are able to exist.
 * Alzheimers will likely occur if too much iron has been digested and accumulated in the brain.
 * Humans need collagen to obtain amino acids to make our own proteins.
 * Humans make their own collagen.