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My world - basically Earth all along, unless told otherwise - is populated by humans and few fantasy-based "races" (actually, species - any interbreed offspring, if possible, is infertile): elves, dwarves, etc. Despite the fact that setting is to some extent inspired by common fantasy tropes, there is no magic at all, just hard science. All "fantasy species" in fact belong to the Homo genus and should be plausibly justified as the effects of natural evolution of (perhaps isolated) groups of hominids.

Elves, in addition to some other stereotypical elvish traits (slender, pointy ears etc.) are known to not eat meat of any mammal or bird, while having no problem with milk, eggs, fish and seafood (insects, amphibians and reptiles are a grey zone, read: I have no idea here).

Sure, I can come up with some cultural reason for this, but instead I would like to actually hardwire this trait somehow in their biology. Meat of mammals and birds should be just inedible, though, not poisonous or otherwise deadly: I don't want them to die just because they ate some food offered by humans!

Why these kinds of meat could be inedible for a hominid?

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    $\begingroup$ the problem hear is there is nothing unique to mammal and bird meat, that is not present in things like eggs, shellfish, dairy, or many plant based foods. $\endgroup$ – John Oct 9 '17 at 5:55
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    $\begingroup$ Why not just make it cultural? $\endgroup$ – RonJohn Oct 9 '17 at 23:19

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Non-metabolizable components in meat proteins accumulate in elves that eat them, causing gradual physical and mental degeneration.

Lectins are cell surface glycoproteins. About 150,000 years ago there was an evolutionary bottleneck, from which the ancestors of humans emerged lacking certain lectins that are still present in our ape relatives. I am sorry I could not find full text. An abstract:

Varki A. Glycoconj J. 2009 Apr;26(3):231-45. Epub 2008 Sep 7. Multiple changes in sialic acid biology during human evolution.

Humans are genetically very similar to “great apes”, (chimpanzees, bonobos, gorillas and orangutans), our closest evolutionary relatives. We have discovered multiple genetic and biochemical differences between humans and these other hominids, in relation to sialic acids and in Siglecs (Sia-recognizing Ig superfamily lectins). An inactivating mutation in the CMAH gene eliminated human expression of N-glycolylneuraminic acid (Neu5Gc) a major sialic acid in “great apes”. Additional human-specific changes have been found, affecting at least 10 of the <60 genes known to be involved in the biology of sialic acids. There are potential implications for unique features of humans, as well as for human susceptibility or resistance to disease. Additionally, metabolic incorporation of Neu5Gc from animal-derived materials occurs into biotherapeutic molecules and cellular preparations - and into human tissues from dietary sources, particularly red meat and milk products. As humans also have varying and sometime high levels of circulating anti-Neu5Gc antibodies, there are implications for biotechnology products, and for some human diseases associated with chronic inflammation.

Evolutionary divergence events in hominids are associated with shuffling of the glycoprotein repertoire.

There are mutations in humans in which the afflicted cannot metabolize certain glycoproteins. Two are the mucopolysaccharidoses. Examples are Hunter's syndrome and Hurler syndrome. The accumulation of the glycoproteins in the body tissue produces characteristic deformities and developmental defects. I will not link images of the kids affected by these syndromes but they look different in a manner characteristic of their disease. Another name for Hurler syndrome is gargoylism.

So your elves: the divergence event that led them to speciate involved a loss of certain glycoproteins, and then also the metabolic capacity to handle these glycoproteins. Just as Neu5GC is in our meat animals but not in us, these glycoproteins are in other mammals, but not elves. When the elves ingest them (just as when human ingest beef) these now-foreign molecules persist in the body (as Neu5GC from meat persists in our bodies). A little bit is ok, but over weeks and months these substances accumulate, causing mucopolysaccharidosis- like physical deformities and mental disease in the elves who eat them. And they know now not to eat them.

This is more interesting, I think that just dropping dead if you eat a meatball. Elves in dire straits could eat some meat. They might even like it; probably they would. But a steady diet of meat will become obvious as the meat eating elf will become thicker featured and less sharp of mind...


In fact, there would be one terrestrial vertebrate whose meat these elves could eat with impunity. Perhaps this would be done for certain ceremonies. Deducing the identity of this animal is left as an exercise for the reader.

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    $\begingroup$ of course these glycoproteins are present in a lot more things than just meat, their diet is going to be very restrictive. $\endgroup$ – John Oct 9 '17 at 5:51
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    $\begingroup$ Is it "gur nafjre znl or ryirf ohg V fnl gung vg vf abg uhznaf"? $\endgroup$ – wizzwizz4 Oct 9 '17 at 15:29
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    $\begingroup$ I think the answer ought to be Ryirf naq zbfg bgure ubzvavqf. Am I right? This answer uses ROT13 $\endgroup$ – Blapor Oct 9 '17 at 21:37
  • $\begingroup$ @wizzwizz is right. Blapor is not, for the same reason that humans in this world can eat beef. But: an up vote for introducing me to the ROT13 key which I had not run across before. Very clever way to post answers and not mess it up for everyone else, you two. $\endgroup$ – Willk Oct 10 '17 at 0:39
  • $\begingroup$ @Will Obviously I stole it from somebody else. It's the spread of knowledge. :-) $\endgroup$ – wizzwizz4 Oct 10 '17 at 18:36
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Red/mammals meat differs from fish meat essentially because of its different content of fats.

You can have your elves lack the enzymes needed to digest highly saturated and/or aromatic fats (cholesterol). That would be enough to give them good reasons to routinely avoid the stuff without preventing occasional usage.

Occasional intake would mostly go unnoticed, but continue would result in diarrhea.

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    $\begingroup$ So essentially similar to my friend who's mostly lactose intolerant but can have a single scoop without problems? $\endgroup$ – chrylis Oct 9 '17 at 1:28
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    $\begingroup$ that will only stop them from eating a few meats, poultry and even many mammal meats will still be completely digestible. And of course many eggs and shellfish are high in cholesterol. $\endgroup$ – John Oct 9 '17 at 5:52
  • $\begingroup$ This would also rule out eggs and milk. $\endgroup$ – Mindwin Oct 9 '17 at 13:15
  • $\begingroup$ @John and others: I pointed out a possible mechanism, I am unaware of any complex molecule that would be present in (relatively) large quantities in mammal meat and not anywhere else. Aromatic fats are a near call, but surely not perfect. Note: diary products are bound to contain much of the same kind of stuff mammal meat does; differentiating may be very difficult. $\endgroup$ – ZioByte Oct 9 '17 at 13:30
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    $\begingroup$ myoglobin, might work it is what makes red meat red after all. At least there will not be any in eggs or dairy. $\endgroup$ – John Oct 9 '17 at 14:15
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I can't think of a way to hardware it into their genetic code, but it is possible to be allergic to red meat and poultry.

(http://acaai.org/allergies/types/food-allergies/types-food-allergy/meat-allergy)

Basically, if someone is bitten by the Lone Star Tick, they can develop an anaphylactic response to eating red meat. If there was something like this in their environment, and became widespread in their population, it could result in a culture wide aversion to eating red meat.

However, if you're worried about death by meat allergy, you could have the elves only develop the more minor symptoms of the allergy. That way eating meat would make them uncomfortable, rather than potentially killing them.

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One approach would be to look at what diseases are more common in pescatarians or ovo-lacto vegetarians, in humans, and then make your elves prone to the opposite of those diseases.

For instance, anemia sometimes occurs when someone switches to a vegetarian diet, due to insufficient iron intake. The opposite condition appears to be called hemochromatosis, where there is too much iron in the body. A predisposition towards hemochromatosis (such as if their body were more efficient at concentrating/utilizing dietary iron) would discourage elves from eating too much red meat - a little bit might be fine, but if they ate it regularly, they'd feel chronically unwell.

If you were to use that approach, there could be some related dietary impacts, as well. For instance, a species which needs a lower-iron diet might eat less spinach than humans do, and would likely avoid foods such as marmite (despite being vegetarian-friendly for humans).

For bird meat, I'm not sure what exactly could cause selective dietary problems. There may be some other nutrient that the elves could be unable to handle in large quantities; or perhaps they eat all lower-iron meats, but not high-iron meat (beef, apparently chicken liver, etc.).

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the problem hear is there is nothing completely unique to mammal and bird meat. that is there is nothing present in all mammals and birds that is not present in things like eggs, shellfish, dairy, or many plant based foods.

The closest I think you can get is to make them a mild food allergy for myoglobin, it is at least unique to vertebrates but the amount varies quite a bit. It can't be too strong an allergy since they have myoglobin in their own muscles. Myoglobin is present in large amounts in most birds and most mammals muscle tissue. It is present in many other animals as well but the levels are very high in those two groups. Red meat is very high in myoglobin, and is linked to several meat allergies (like beef allergies), your elves will still be able to eat (most)fish just fine and a few low myoglobin mammal and bird meats (for instance opossum meat and poultry white meat is very low). But most mammal and bird meats will elicit a reaction.

Myoglobin is only present in muscle tissue so there will not be any in eggs or dairy.

So some rare poultry and mammal meats will be edible but many/most will not. But you could easily make this reaction to most mammal and bird meats a basis for a general psychological aversion to mammal and bird meat in general. If eating any meat becomes a gamble they could easily develop a taboo against terrestrial meat in general.

note there are a few fish that are high in myoglobin, so no red tuna for your elves. They may start avoiding any red fish meat as well, this is rare at least so they may still see other fish as perfectly edible.

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    $\begingroup$ They're elves ! If your story depends on elves not having myoglobin in their muscles, then let that be the truth. $\endgroup$ – MSalters Oct 9 '17 at 15:20
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    $\begingroup$ Well there are human with myoglobin allergies, and humans most definitely have myoglobin in their muscles, so I see no reason they can't have myoglobin. But you are right they do not need myoglobin, rats without myoglobin seem to do just fine. ncbi.nlm.nih.gov/pubmed/9804424 $\endgroup$ – John Oct 9 '17 at 15:29
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You could make it so that eating seafood is a necessary dietary constraint. So rather than having the elves avoid eating other land-based meats, they have evolved to where certain required nutrients are only found in seafood.

For example, humans require vitamin C in their diets, but other mammals typically do not. This is because while vitamin C is required for most/all mammals, most of them can manufacture their own. Humans, however, lost that ability some time ago, but this defect persisted (rather than killing off those with the bad gene) because of an abundance of food with vitamin C in the area where they lived. It only became a problem when humans moved out of the tropics and started taking long voyages without adequate vitamin C laden foods.

So your elves may have evolved in an area where they anciently ate mostly fish, and their bodies mutated leaving them dependent on some nutrient in the fish. They now need to regularly eat fish, rather than red meat or poultry, thus they would be primarily pescatarian. This would not mean that the other meats would be poisonous, just that over time the elves would not be able to survive on only land meats.

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Teeth

Other suggestions delve in biochemistry, but I can suggest an anatomy way: they lack "meat" teeth. We, humans of this world, have sharp, "meat" teeth in front and flat, grinding "plant" teeth on sides. This allows us to chew everything.

If elves have only flat teeth, or may be even soft teeth, like wales do, it will be a real chore to bite off and chew meat due to its consistency. Thus, prehistoric elves avoided it altogether, and nowadays they can technically cook it edible, but meat is just not in their culture.

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Evolution works by killing fertile individuals before they reproduce. Harsh, but simple to consider.

Now your stereotypical elf doesn't have kids at a young age - they have a long lifespan after all, and your world doesn't suffer from massive overpopulation. So fertility must be fairly low. Perhaps they get kids at age 200-300.

This means that anything which kills them in <200 years is evolutionary bad and selected against. Now, if consuming red meat causes heart attacks in 150 years, the ability to eat and process red meat would be a clear disadvantage. Those elves that digested red meat less well would have a larger chance of survival.

TL:DR: Red meat kills elves before they have offspring, driving evolution.

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I'd say something psychological. Elves, in fiction, are known for their love of nature and such. If they eat something that came from a sentient being, it's possible that they start breaking out in hives, or become sick, not because they have a species-wide allergy, but because of their culture.

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I'd say make their genetic history favor not eating meat, maybe it's not very good for the elves. Meat would therefore taste bad for elves. They would still be able to eat it, somewhat.

I wouldn't go for the route where it's entirely inedible, but that's just me.

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  • $\begingroup$ The question here is precisely about why they do not favor it. $\endgroup$ – pipe Oct 10 '17 at 14:56

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