Humans are not herbivores

An image that constantly circulates in various places is this:

05_Humans_Are_Frugivores_750

As much as I agree with veganism, distorting facts to make a point is not the way to go. In fact, it’s counterproductive.

Definitions

 Herbivore

An herbivore is an organism that feed exclusively or mainly on plants. Herbivores typically have adaptations towards a specialization of eating and digesting plant matter. This could include but is neither limited to nor has to have flatter teeth to grind plant matter, long intestines, gut microbiome to digest cellulose and other hard-to-digest parts of plants.

 Carnivore

A carnivore is an organism that feed exclusively or mainly on animal tissue. As herbivores they typically have adaptations towards specialization of eating animal tissue such as sharp teeth, short gut and some way of capturing prey, such as claws, ability to sprint or venom.

 Omnivore

Omnivores are organisms that feed on both animal tissue and plants. There is no strict definition of how large portion of the diet that has to be, to be classified as omnivore. Omnivores typically lack specializations to either animal or plants, and have more intermediate traits.

Classifications

Class of diet is not a taxonomic taxon – that is a unit in biological classifications (the science of taxonomy) such as genus or species. Carnivora however, is a taxon; it includes among others felines and bears. Not all members of Carnivora are carnivores. It includes carnivores, omnivores and herbivores.

The herbivore, carnivore and omnivore diet classifications is a classification based on what diet an animal generally have, not what it couldhave. Neither does it reflect evolutionary relationships, even though they might correlate in some instances.

A clear example how this is true is that you’ll find carnivores that are cats, fungi, worms and even plants.

Within biology, humans are clearly regarded as omnivores (Ley et al., 2008).

Evolution

Before we get into evolutionary arguments. Let’s just get some common misconceptions clear first. Humans did not evolve from the chimpanzee or any other now-living primate. Humans didn’t evolve from great apes to be something else; we are great apes – or Hominidae. Humans share a common ancestor with chimpanzees, actually humans share common ancestors with every single organism ever existed if you go back long enough. Since chimpanzees and humans are closely related, humans share a much more recent ancestor with chimpanzees than for example a horse.

phylo

In the image above, the species A, B and C is different species. A and B is more closely related than A and C, and B and C. Where the arrow points is the most recent common ancestor between A and B. That doesn’t mean that A evolved from B, but that A and B evolved from an ancestral species that diverged into A and B. This species didn’t look neither like A nor B. At the very root of the tree lived a species that is the common ancestor between A, B and C. One important point though is that A, B and C are equally distant from the species at the root of the tree.

Lastly, and this might be the most important one: Evolution is not teleological. Evolution does not have a purpose, aim or goal. There is no such thing as more evolved or de-evolution. Humans are not more evolved than chimpanzees; we just diverged in different direction. The quantitative unit of evolution is time, and as far as I know humans has not evolved longer than chimpanzees. Evolution is the change of living organisms over time that depend on many factors, but a lot less chance than some people think, and no planning ahead what so ever. No are created to be food.

Human evolution = loss of sanity

What I mean with that subtitle is that, when people reflect over human evolution to construct an argument, often they lose the ability to view the human species objectively and transform humans into something completely separated from the rest of the vast number of species on earth. Humans are unique, but so are every single species on earth. Some people even claim that human evolution has stopped, and that of course is utterly ridiculous.

I’d like to present something I’d like to call the ‘Alien David Attenborough thought experiment‘: Imagine that you are an alien biologist travelling from a distant planet to study life on earth (I like to use David Attenborough’s voice to narrate this, that’s all). You study all the different species, describing behavior, diet and appearance. When you start describing humans, what diet would you assign humans to have? What behaviors would you ascribe humans? If I would do it, I would certainly not say: “Homo sapiens diet has for thousands of years included meat in some populations, and less in some, but really, they are made for fruit” neither would I say: “Humans live in artificial buildings and wear fabric clothing, this is however a very unnatural state for the Homo sapiens species”. I think that this could be a nice strategy to get away from an anthropocentric prison of mind.

The ancestors of Homo sapiens cooked their food, cooking has been around for approximately a million year (that is around 500 000 years longer than the human species has existed) (Berna et al., 2012; Organ, Nunn, Machanda, & Wrangham, 2011). Traces of humans eating meat is also ancient and seems to have been around for as long as our species existed (Pobiner, 2013). One of our closest relatives the chimpanzee also eats an omnivorus diet with mainly fruits, but occasionally eats animals (McGrew, 1983).

Reflecting to my previous discussion, saying that meat-eating is unnatural because we need to cook it (which we don’t) is a flawed argument. Likewise is the claim that we need to be able to hunt down grazing prey with our bare hands,kill and eat it raw a flawed argument. Due to our highly developed brain, we don’t need that, we find other ways. That trait is no stranger than a lions teeth.

The whole idea of finding an ancient diet that we are “made” for, is just absurd, we are not exactly the same as pre-historic humans. The changes in our environment have led to several adaptations regarding diet. For example, mammals give their young mother’s milk (that is the very definition of mammal). This stops at a certain age and the offspring is able to eat as their parents. Milk contains lactose and mammals have an enzyme called lactase to digest lactose. When the child stops receiving milk, the expression of this enzyme is turned off. However, in some human populations this enzyme remains active through adulthood, which is referred to as lactase persistence. This is thought to be an adaptation to the habit of drinking milk from domesticated animals (Tishkoff et al., 2007).

A different relatively recent human adaptation is a duplication of the gene AMY1 that encodes an enzyme called amylase that digests starch. Duplication of genes typically result in an increased production of the enzyme, thus this is hypothesized as being an adaptation to the use of agriculture which would increase the amount of starch in the diet (Perry et al., 2007). For these adaptations we are talking about, we are in a time frame of ~10 000 years.

Here I really like to emphasize that the naturalistic fallacy of equating a ‘is’ with a ‘should’, is something we really should avoid. The fact that humans have eaten meat and drinking milk is no argument that we should, unless we had to (we don’t).

Cherry picking

I feel that this deserves an own paragraph to just think a bit about cherry picking. The image this discussion started from is guilty of cherry picking on several points. So what is cherry picking? Usually multiple data sets or data points exists in a particular case. For example, global warming, many research groups around the world has published articles with data measuring the effect of global warming. Since data contains noise and bias in addition to signal, the data will fluctuate in varying degree. If one has a specific viewpoint and then choose only to look at the data that verifies that viewpoint, and disregard data that is contradictory without relating to it is cherry picking. Look at this plot here:

cherry

If a cherry picker chooses only to look at the data points where the arrow points, the cherry picker might miss the general upward trend. The second point is an outlier and might be just due to noise.

This is why we in science do meta analysis and repeat experiments by other groups to verify results before they even come close to be regarded as facts.

Cherry picking is basically confirmation bias in practice, but also it is related to anecdotal evidence, where a person claims something based only on an anecdote. This is bad science, and something that is easy for everyone to fall into if one is not aware of the cognitive biases one has. But it’s a completely different thing to do it deliberately to prove a point. Yes, I’m looking at you alternative medicine promoters who use books by single “Dr”s as proof of ideas completely contradictory to everything we know.

Dissection

I’ve been building a theoretical background now for the case, which should apply for similar claims of humans being herbivores or “made for plants” or whatever, but let’s spend some time on this image:

05_Humans_Are_Frugivores_750

First of all, it is obvious that the point of this image is to try and show that humans are “frugivores” thus, more like the primate (which I really cannot identify the species of, not a primatologist). Please note that just due to shared evolutionary history, we will be more similar to a primate in many cases simply by that.

Secondly, frugivores are basically omnivores. Frugivores are usually used as a term for omnivores that feed on fruit. Most frugivores do not eat exclusively fruit. Anyway, orangutans are usually referred to as frugivorous. Take a look at this orangutan skeleton and look at those canines. Just as a contrast for that – cherry picked – image representing all frugivores.

Orang-Utan_Tournai

So let’s go down the table and just stop and think at every row.

Physiological food: What the hell is that? A platonic diet?

Hands/legs: Is this reflecting adaptation towards specific diets? I think not.

Walking: Well this is obviously cherry picked to fit the idea. These walking styles are in no way representative of diet. Some primates walk upright, and many primates are omnivores.

Mouth opening: Again, is this evidence for specialization? The image tries to imply that only meat eaters have large mouths, what about hippos?

Teeth: Human teeth look neither like an herbivore or a carnivore. Again, cherry picking away, what would happen if you used a panda as representative of herbivore teeth?

Chewing: This behavior is clearly related to what type of food you are actually eating and not a fixed behavior that is a clear adaptation to specialization of food. Some foods needs to be chewed more to swallow.

Saliva: As discussed above, humans have adapted to eating starch from agriculture. Omnivores are expected to handle both vegetable matter and animal tissue, so this is nothing strange.

Urine: The urine is the body’s way of excreting waste products, regulating water balance and body pH levels. The pH is dependent on what one eats. A high protein diet is causing acidic urine; an animal does not have a carnivorous diet because it has acidic urine (Rose, Parker, Jefferson, & Cartmell, 2015).

Urate oxidase: Humans and other higher apes have this gene, but it’s not functional. Otherwise this is present in virtually all organisms. Apes are outliers in that sense.

Gastric acid: This is simply wrong. Human gastric acid has a pH of 1.5 – 3.5 which is highly acidic (Lehrer, 2014)

Fibers and cholesterol: This might be true, but it’s mainly carnivores that really need these traits. I don’t know if this is representative of the given groups, but from what you might notice, you shouldn’t trust the image.

Sweat: Humans are like omnivores in this sense even according to the image.

Intestines: As one might expect from an omnivore the intestines have an intermediate relative length between carnivores and herbivores.

Short alkaline colon: Here my guess would be that since a bear is chosen as a representative for omnivores – which are closely related to carnivorous polar bears, It might be the reason why omnivorous bears are biased towards carnivoury.

Cellulose: Humans are like omnivores in this sense even according to the image.

Digestion: As one might expect from an omnivore the digestion time according to the image is an intermediate between carnivores and herbivores.

With that being said, there are additional problems one would face if one would claim that humans aren’t omnivores. Humans are not able to synthesize sufficient b12 in the gut, neither can humans acquire b12 from any other source than animal origin or artificially fermented – supplements https://en.wikipedia.org/wiki/Vitamin_B12 (accessed: 04/01/2016). Additionally humans absorb iron form heme-sources most efficiently. That food that contains blood (West & Oates, 2008).

I’ve said it earlier and I say it again. This is not an argument for not being vegan. Humans are omnivores, but can live on a completely vegan diet with the supplementation of B12 from fermentation. I think that trying to claim that humans are something else than omnivores are just counter productive since it’s quite easily debunked and we lose credibility. There are plenty of reasons to be vegan and still stick to what is true. This post is mainly focused on debunking the claim that humans are herbivores and should therefore eat only plants, but the post should qualify to debunk anyone claiming that humans are biological meat eaters and therefore should eat meat, likewise.

And hey! This is the longest ever debunking of a meme I ever done, and probably will do. Memes are stupid

References

Berna, F., Goldberg, P., Horwitz, L. K., Brink, J., Holt, S., Bamford, M., & Chazan, M. (2012). Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa. Proceedings of the National Academy of Sciences , 109 (20 ), E1215–E1220. doi:10.1073/pnas.1117620109

Lehrer, J. K. (2014). Stomach acid test. Retrieved January 4, 2016, from https://www.nlm.nih.gov/medlineplus/ency/article/003883.htm

Ley, R. E., Hamady, M., Lozupone, C., Turnbaugh, P. J., Ramey, R. R., Bircher, J. S., … Gordon, J. I. (2008). Evolution of Mammals and Their Gut Microbes. Science , 320 (5883 ), 1647–1651. doi:10.1126/science.1155725

McGrew, W. C. (1983). Animal foods in the diets of wild chimpanzees (Pan troglodytes): Why cross-cultural variation? Journal of Ethology, 1(1-2), 46–61. doi:10.1007/BF02347830

Organ, C., Nunn, C. L., Machanda, Z., & Wrangham, R. W. (2011). Phylogenetic rate shifts in feeding time during the evolution of Homo. Proceedings of the National Academy of Sciences , 108 (35 ), 14555–14559. doi:10.1073/pnas.1107806108

Perry, G. H., Dominy, N. J., Claw, K. G., Lee, A. S., Fiegler, H., Redon, R., … Stone, A. C. (2007). Diet and the evolution of human amylase gene copy number variation. Nat Genet, 39(10), 1256–1260. Retrieved from http://dx.doi.org/10.1038/ng2123

Pobiner, B. (2013). Evidence for Meat-Eating by Early Humans. Nature Education Knowledge, 4(6), 1. Retrieved from http://www.nature.com/scitable/knowledge/library/evidence-for-meat-eating-by-early-humans-103874273

Rose, C., Parker, A., Jefferson, B., & Cartmell, E. (2015). The Characterization of Feces and Urine: A Review of the Literature to Inform Advanced Treatment Technology. Critical Reviews in Environmental Science and Technology, 45(17), 1827–1879. doi:10.1080/10643389.2014.1000761

Tishkoff, S. A., Reed, F. A., Ranciaro, A., Voight, B. F., Babbitt, C. C., Silverman, J. S., … Deloukas, P. (2007). Convergent adaptation of human lactase persistence in Africa and Europe. Nat Genet, 39(1), 31–40. Retrieved from http://dx.doi.org/10.1038/ng1946

West, A. R., & Oates, P. S. (2008). Mechanisms of heme iron absorption: Current questions and controversies. World Journal of Gastroenterology : WJG, 14(26), 4101–4110. doi:10.3748/wjg.14.4101

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203 thoughts on “Humans are not herbivores

  1. Good blog – some of the comments on here are a little rude and argumentative, but that is their prerogative. Science is science and not all things can be proven, we are only human and led by people we think have the knowledge. Don’t forget recently we were advised that the medical books had to be altered to say that lymph nodes are also found in the skull/brain. Everything is a learning curve. Being a vegan is someone’s choice as long as you feel well then carry on…….

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  2. Fantastic debunk. I personally have a very balanced diet, which I am extremely happy with and thankfully I am healthy!. I have been looking for intellectual an elegant article to give to a rather ‘force upon the world their views’ friend about this exact subject. I have always believed people can choose their (within obvious margins) diet but not force their opinions on it to other people (much like many other things!

    I think this statement is extremely important ‘This is not an argument for not being vegan. Humans are omnivores, but can live on a completely vegan diet with the supplementation of B12 from fermentation’. This is how it should be talked about.

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  3. I appreciate this article. Humans are omnivores. Diet may not be by choice, but by health. This, however, does not change the fact that humans are omnivores. Unlike dogs, humans can live without meat in their diets. Not to be rude, but I would rather this article was reviewed for grammar before being posted. It is my fear it loses some clout due to grammar issues. In truth, I feel it is a well researched article that points out flaws seen in other articles that render them more unprofessional than mere grammar issues can. Education regarding vegan and vegetarian diets would be more helpful than “slamming” those who enjoy the taste of meat.

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  4. Thank for you the lack of bias and the references; you even explained cherry picking. I was sceptical when I saw “veganbiologist.com” (in terms of bias) but thankfully I finally found a vegan or plant-based diet focused website that isn’t clinging to the notion that the reason we should only eat plants is because we are herbivores…that really grinds my gears.

    Admittedly I’m only a vegan for selfish reasons; I believe it’s the best diet for my health. Yet if there was science to prove a carnivorous diet was more healthy then I’d eat meat exclusively. For that reason, thank you for trying to remaining objective.

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