Humans are natural meat eaters.

I am arguing that human beings ARE natural meat eaters.[For the following, the word “meat” encompasses all animal tissue, i.e. mammals, reptiles, birds, insects, fish, etc.]TL;DR - I argue that human beings have had a long history to do with meat eating, such a history has given humans natural predispositions to eat meat, I show that humans have evolved many genetic, physiological, nutritional, and morphological adaptations for meat eating. _______(all sources are linked in the blog at the end of this post)Based on fossil and isotonic evidence we can see that ever since humans came to be (and the Genus "Homo" originated), 2.5 million years ago, humans have eaten animal matter. Before meat became a large part of our diet our ancestors likely had a diet similar to that of chimpanzees, mostly a herbivorous diet consisting of fruit, seeds, nuts, leaves, flowers, and yes, a very small portion of animal matter. Today, however, meat makes up a large source of our diet, it is estimated by the OECD and FAO that the world consumed about 14500 tonnes of sheep meat, 68000 tonnes of beef and veal, 116000 tonnes of pork and 116000 tonnes of poultry in 2016.Since humans have eaten meat for such a long time and that meat is still eaten in large quantities today you would think that it is completely natural for humans to eat meat.Some people, however, don't think so, suggesting that eating meat is merely a habit we perform.To prove the point that we are indeed natural meat eaters I have compiled many possible adaptations in humans for meat eating. They consist of morphological, physiological, genetic, and nutritional adaptations:(Please note before you read these adaptations that just because they exist doesn't mean we have to eat meat or that we can't live healthily without eating meat.)Nutritional adaptations-1) Vitamin B12 - The natural source for cobalamin in human is via the eating of animal products, as there are very few plant sources containing significate amounts of cobalamin, which likely would not have made up a significant portion of the human diet as we evolved. Herbivores get most their cobalamin from gut bacteria which synthesize the vitamin. In humans, however, it is unlikely that gut bacteria are able to act as a significant source of cobalamin, due to the fact that cobalamin produced by gut microbes represents a miniscule amount (about 2%) of the total corrinoid content in faeces and that it is produced in the colon, which is below the small intestine where cobalamin can be absorbed. This evidence suggests an adaptation to meat eating, in order to get the required amount of B-12. This conclusion gains even more support when studying people on vegetarian and omnivorous diets, which finds that there are lower levels of B12 in vegetarian and vegan diets and that vegetarians and vegans are at high risk of B12 deficiency than people who eat some meat.2) Taurine synthesis - Our species has a limited ability to synthesize is the biologically important amino acid, taurine.Vegetarian and vegan’s diets in human’s result in lowered concentrations of taurine, which is found naturally in meats and fish, but hardly ever in plants. Like felines the need to internally synthesize taurine may have been evolutionarily reduced in humans because it had been obtained in the diet, which had relaxed the selective pressure formerly requiring the need to synthesize this essential amino acid.3) 20 and 22 carbon fatty acids- Like obligate carnivores, humans have an ineffective ability to chain elongate and desaturate 18 carbon fatty acids to form their product 22 and 20 carbon fatty acids. Since these fatty acids are crucial for the function of the cell membrane and brain tissue among other things this could cause a problem if we didn't get enough of the fatty acids. This indicates 22 and 20 carbon fatty acids must have been obtained via the diet, 20 and 22 fatty acids are found mostly in animal food. Although they can be found in plant foods the amount in plant sources are only trace quantities, and it is more likely that animal tissue was the main source of 22 and 20 carbon fatty acids available to our Hominid ancestors.Physiological and morphological adaptation-1) Dental anatomy- Analysis of teeth from early Homo species have shown that early Homo’s teeth are adapted to eat tough food, meaning early Homo was more adapted to fracture tough, pliant foods. Meat seems to be most likely be this key tough-food resource, as one of the other main sources of tough-foods early Homo could have obtained sufficiently to cause this adaptation in the teeth. Reviews of dental evidence of our ancestors which analyze Dental Microwear, Dental Structure, Occlusal Morphology and Tooth size have changed suggesting a shift in diet in early Homo and especially H. erectus with broadening of diet to include at least some more tough foods.2) Gut morphology- Carnivores and herbivores have morphological differences in their gut. Carnivores tend to have well-developed stomachs and long small intestines, herbivores tend to have a chambered stomach with well-developed caecum and colon. Humans fit neither of these patterns. The human gut has a simple stomach, relatively elongated small intestine and reduced caecum and colon. Which suggests a relatively high dependency on meat. BUTanalysis of whether the human gut specification fits a preferred faunivorous or frugivorous diet often yields contradictory results depending on which technique is used, some methods give results that the gut is firmly in the faunivory range and others suggesting the frugivore range. However, the human gut is probably more firmly implanted into the frugivore range, similar to that of organisms which eat mostly fruit with the inclusion of a large portion of insects and small amounts of vertebrates. 3) Haem Absorption- Humans have the ability to digest haem iron due to intestinal receptors, which are specifically for the absorption of heme iron. Although heme iron is found in plants at very low levels, the amount in plants is not nutritionally significant, and heme iron is sourced almost entirely from animal foods (Which also explains why vegetarians are more prone to very low iron levels and status than people who eat meat). Other possible adaptations-1) Meat-adapted genes- There are some genes in the human genome that are adaptations to eating meat. Some hypothesise that the increased consumption of animal sourced food during human evolution, selected for “meat-adaptive genes” to increase resistance to harmful effects of fat, toxins, and pathogens, delaying dysfunctions and diseases of the brain and heart, etc. caused by this increasingly meat-rich diet. And enable a major increase in life span. However, this is just a hypothesis at the moment and requires further research to be verified, for example an alternative hypothesis is that there might be a genetic basis for food preferences, affecting the choice of meat in human diet. Either way the human genome has adaptations (or inclinations) for meat eating.2) Co-evolution with parasites- Cestodes of the family Taeniidae are parasites of carnivores spread by eating meat. Taenia saginata (commonly known as “beef tapeworm”) and T. solium (commonly known as “pork tapeworm”) use humans as their definitive host, whereas these parasites are not definitive for the other great apes. This parasite which specifically lives of humans indicates a substantial period of coevolution and meat consumption by humans and their ancestors. It is hypothesized that dietary shifts by humans from herbivory to increased carnivory during the evolution of early Homo caused these parasites to start infection humans.Finally, it's the end...For now anyway.Sources: https://undrscope.wordpress.com...