Are humans omnivores or herbivores?

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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?

Humans are omnivoresEdit

Omnivores are animals anatomically and physiologically adapted to eating both plant and animal matter.

Arguments forEdit

  •   Argument for Humans gain significant nutrition and energy from meat.
    •   Objection Animal products contain components which cause many prevalent chronic diseases, amongst which cholesterol, which causes the inflammation of the arteries and can lead to atherosclerosis,[1] cardiovascular disease and strokes
      •   Objection Your opinions and generalizations of animal products are unrelated to the discussion
      •   Objection Not all animal products do. That is a generalization
    •   Objection 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
      •   Objection 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, and i mean EXCESSIVE.
    •   Objection Behavior only tells us what we already know, and we are all accutely aware that meat eating is a common practice, but so is traveling via airplane. I.e., the fact that so many of us do this however, doesn't mean we have specific physiological adaptations towards this behavior.[2][3]
  •   Argument for Humans have a trophic level of 2.21 (same as anchovy and pigs).[4] Anchovy subsist primarily on zooplankton,[5] and pigs are omnivores. Animals with such a trophic level can subsist on a widely varied diet.
    •   Objection 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.
  •   Argument for Our closest evolutionary relatives, chimpanzees and bonobos, are omnivores.[6][7] As their biology most closely resembles ours, it's more likely that humans are omnivores too.
    •   Objection Only a 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.
      •   Objection Carnivores have also been reported eating plants.[8][9] 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.
  •   Argument for Humans wean earlier than herbivores, a pattern that matches that of carnivores.[10] 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,[11] which is considerably shorter than in chimpanzees and orangutans, even accounting for cultural differences and individual preferences.
    •   Objection Many herbivores wean earlier than humans, such as cattle and sheep.
    •   Objection 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.
      •   Objection 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 cases).
      •   Objection People can be intolerant as a baby without ever having taken animal milk.
  •   Argument for Humans are able to digest meat and absorb its nutrients, which we would be unable to do if we were herbivores.
  •   Argument for 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 were designed to hunt and eat other species.
    •   Objection Many predators don't have forward-facing eyes, and many herbivores have forward-facing eyes.
    •   Objection Humans descend from tree-dwelling animals, that needed precise forward-looking binocular vision to avoid falling when leaping and moving around.
  •   Argument for The vast majority of humans practice an omnivorous diet and have been doing so for millions of years, and many live a long, healthy life.
    •   Objection Humans who eat a vegetarian or vegan diet tend to live longer and are less prone to various diseases and conditions, it has been proven that it is healthier to lead a vegetarian life.
    •   Objection 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.
      •   Objection For the most part, "omnivore", "carnivore" and "herbivore" have historically been defined by behavioral measures. Numerous species that have previously been defined as herbivores, including hippopotamus,[12][13] sheeps and cattle,[14][15] and many others[16][17],[18][19][19] 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.
  •   Argument for Omnivorous behavior in humans is a cultural universal (with few exceptions like Jains, Amish and Hindus). There is considerable evidence that such cultural universals can be attributed to our genetics, and in turn to our physiology.[citation needed]
  •   Argument for 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.[citation needed]
    •   Objection Those nutrients are not essential for human health.[citation needed]

Arguments againstEdit

  •   Argument against If humans were meant to eat meat, why would nature dictate that we have to cook or cure to make it safe for consumption?
    •   Objection 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 the ancestors of H. sapiens 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.
  •   Argument against Only anatomical herbivores develop atherosclerosis when exposed to high levels of saturated fat and cholesterol. Animals with sufficient physiological adaptations to eating 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 pesist even after cooking) mean it is just not what's best for our anatomy.
    •   Objection No one is arguing for food with high levels of fats or cholesterol, but for natural meat or vegetables.

Humans are herbivoresEdit

Herbivores are animals anatomically and physiologically adapted to eating plant material as the main component of their diet.

Arguments forEdit

  •   Argument for Some of our closest evolutionary cousins (chimpanzees, bonobos, gorillas) are herbivores.
    •   Objection Deers, chimps and bonobos frequently eat termites, ants and other insects, which are still meat.
      •   Objection 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.[20]
    •   Objection Chimps have been documented hunting and eating small mammals.[21] Besides, the source[20] states omnivores as opportunistic feeders.
  •   Argument for Humans lack claws, sharp teeth or other natural weapons.
    •   Objection The invention of tools for hunting prey meant there was no longer a need for costly evolutions such as claws and sharp teeth that did not fit a purpose. No longer requiring claws because easier to craft tools fit the purpose also contributes to increased manual dexterity, which was a key component in human evolution.
      •   Objection Human evolution did not change so much since humans developed tools that accounts for this
    •   Objection Our natural weapon is our brain, which can and is used to make other weapons and strategies.
  •   Argument for 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.
    •   Objection 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.

Arguments againstEdit

  •   Argument against We should ask the question: can we really be defined as herbivores/carnivores? People have been eating what they have for years and have demonstrated that it is possible to live a lifetime under all diets, thus human is empirically onmivorous.
  •   Argument against 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.
    •   Objection 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.
      •   Objection 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.
      •   Objection 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.
  •   Argument against Humans require vitamin B12 in their diet, unlike herbivores which can make their own in their colon with the help of bacteria.
    •   Objection 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.
      •   Objection 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.[citation needed]
        •   Objection Cattle can´t either get B12 and those 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.
          •   Objection 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.
  •   Argument against Our hunter-gatherer ancestors hunted for millennia. If humans were not omnivores, why are we attracted to the physical properties of meat.
    •   Objection To feel attracted is not an argument. It is likely that eating meat was done largely due to the scarcity of calories from any source, plant or animal.
    •   Objection A human baby is not attracted to kill a small animal when it is shown one. On the other hand, the desire to hunt is so deeply embedded in a kitten that they will chase mice instantly.
      •   Objection 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.
      •   Objection What's more, 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".[Summarise and abbreviate]
  •   Argument against Humans selectively absorb heme iron in the small intestine with specialized receptors. No herbivore does this.[citation needed]
    •   Objection Heme iron has been shown to cause heart diseases and alzheimer.
      •   Objection Heme iron is present in plants as well- this is why foods such as the Impossible Burger are able to exist.
      •   Objection Alzheimers will likely occur if too much iron has been digested and accumulated in the brain.
  •   Argument against Humans need collagen to obtain amino acids to make our own proteins.[citation needed]
    •   Objection Humans make their own collagen.

See alsoEdit

Notes and referencesEdit

  1. Ludewig, Burkhard; Zinkernagel, Rolf M; Hengartner, Hans (2002-05-01). "Arterial Inflammation and Atherosclerosis". Trends in Cardiovascular Medicine 12 (4): 154–159. doi:10.1016/S1050-1738(01)00166-9. ISSN 1050-1738. http://www.sciencedirect.com/science/article/pii/S1050173801001669. 
  2. "Mechanism of colorectal carcinogenesis triggered by heme iron from red meat". Biochimica et Biophysica Acta (BBA) - Reviews on Cancer 1873 (1): 188334. 2020-01-01. doi:10.1016/j.bbcan.2019.188334. ISSN 0304-419X. https://www.sciencedirect.com/science/article/pii/S0304419X19301817. 
  3. "Meat, fish & dairy". World Cancer Research Fund. 2018-04-24. Retrieved 2020-09-23.
  4. Bonhommeau, S.; Dubroca, L.; Le Pape, O.; Barde, J.; Kaplan, D. M.; Chassot, E.; Nieblas, A.-E. (2013-12-02). "Eating up the world's food web and the human trophic level". Proceedings of the National Academy of Sciences 110 (51): 20617–20620. doi:10.1073/pnas.1305827110. ISSN 0027-8424. https://www.pnas.org/content/110/51/20617. 
  5. Bacha, M.; Amara, R. (2009-11-10). "Spatial, temporal and ontogenetic variation in diet of anchovy (Engraulis encrasicolus) on the Algerian coast (SW Mediterranean)". Estuarine, Coastal and Shelf Science 85 (2): 257–264. doi:10.1016/j.ecss.2009.08.009. ISSN 0272-7714. https://www.sciencedirect.com/science/article/pii/S027277140900393X. 
  6. Watts, David P.; Potts, Kevin B.; Lwanga, Jeremiah S.; Mitani, John C. (2012). "Diet of chimpanzees (Pan troglodytes schweinfurthii) at Ngogo, Kibale National Park, Uganda, 1. diet composition and diversity". American Journal of Primatology 74 (2): 114–129. doi:10.1002/ajp.21016. ISSN 1098-2345. https://onlinelibrary.wiley.com/doi/abs/10.1002/ajp.21016. 
  7. "Primate hunting by bonobos at LuiKotale, Salonga National Park". Current Biology 18 (19): R906–R907. 2008-10-14. doi:10.1016/j.cub.2008.08.040. ISSN 0960-9822. https://www.sciencedirect.com/science/article/pii/S0960982208011172. 
  8. Lion Eats GRASS, retrieved 2021-03-16
  9. Big Cats Eat Watermelons!?, retrieved 2021-03-16
  10. Psouni, Elia; Janke, Axel; Garwicz, Martin (2012-04-18). "Impact of Carnivory on Human Development and Evolution Revealed by a New Unifying Model of Weaning in Mammals". PLoS ONE 7 (4). doi:10.1371/journal.pone.0032452. ISSN 1932-6203. PMID 22536316. PMC PMCPMC3329511. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3329511/. 
  11. Dettwyler K. A time to Wean: The Hominid Blueprint for the natural age of Weaning in Modern Human Populations. In: Stewart-MacAdam P, Dettwyler KA, editors. Breastfeeding: Biocultural Perspectives. New York: Aldine deGruyter; 1995.
  12. Dorward, Leejiah Jonathan (2015). "New record of cannibalism in the common hippo, Hippopotamus amphibius (Linnaeus, 1758)". African Journal of Ecology 53 (3): 385–387. doi:10.1111/aje.12197. ISSN 1365-2028. https://onlinelibrary.wiley.com/doi/abs/10.1111/aje.12197. 
  13. Dudley, Joseph P.; Hang'Ombe, Bernard Mudenda; Leendertz, Fabian H.; Dorward, Leejiah J.; Castro, Julio de; Subalusky, Amanda L.; Clauss, Marcus (2016). "Carnivory in the common hippopotamus Hippopotamus amphibius: implications for the ecology and epidemiology of anthrax in African landscapes". Mammal Review 46 (3): 191–203. doi:10.1111/mam.12056. ISSN 1365-2907. https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12056. 
  14. PIETZ, P.; GRANFORS, D. (2000). "White-tailed Deer (Odocoileus virginianus) Predation on Grassland Songbird Nestlings". The American Midland Naturalist 144 (2): 419. doi:10.1674/0003-0031(2000)144[0419:WTDOVP]2.0.CO;2. ISSN 0003-0031. https://scienceblogs.com/tetrapodzoology/2010/12/20/carnivory-in-cows-and-deer. 
  15. Furness, R. W. (1988). "Predation on ground-nesting seabirds by island populations of red deer Cervus elaphus and sheep Ovis". Journal of Zoology 216 (3): 565–573. doi:10.1111/j.1469-7998.1988.tb02451.x. ISSN 1469-7998. https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1111/j.1469-7998.1988.tb02451.x. 
  16. "Field Cameras Catch Deer Eating Birds—Wait, Why Do Deer Eat Birds?". io9. Retrieved 2021-03-16.
  17. Clauss, Marcus; Lischke, Andreas; Botha, Heike; Hatt, Jean-Michel (2016-02-01). "Carcass consumption by domestic rabbits (Oryctolagus cuniculus)". European Journal of Wildlife Research 62 (1): 143–145. doi:10.1007/s10344-015-0980-y. ISSN 1439-0574. https://doi.org/10.1007/s10344-015-0980-y. 
  18. "Primate hunting by bonobos at LuiKotale, Salonga National Park". Current Biology 18 (19): R906–R907. 2008-10-14. doi:10.1016/j.cub.2008.08.040. ISSN 0960-9822. https://www.sciencedirect.com/science/article/pii/S0960982208011172. 
  19. 19.0 19.1 Craig, David P. (1998). "Chipmunks Use Leverage to Eat Oversized Eggs: Support for the Use of Quail Eggs in Artificial Nest Studies". The Auk 115 (2): 486–489. doi:10.2307/4089210. ISSN 0004-8038. https://www.jstor.org/stable/4089210. 
  20. 20.0 20.1 "Opportunistic Organism | Encyclopedia.com". www.encyclopedia.com. Retrieved 2020-09-23.
  21. Watts, David P.; Mitani, John C. (2002-02-01). "Hunting Behavior of Chimpanzees at Ngogo, Kibale National Park, Uganda". International Journal of Primatology 23 (1): 1–28. doi:10.1023/A:1013270606320. ISSN 1573-8604. https://doi.org/10.1023/A:1013270606320. 

External linksEdit