Intro
Omnivor is a consumption classification for animals that have the capability to obtain energy and nutrients from materials originating from plant and animal origin while Herbivore is an animal that does the same but from plants only. For the longest time humans have been considered omnivores(with a mostly carnivorous diet) because we consume both meat and plants, but that observation has been primarily made due to human behavior but what does our anatomy agree or disagree with this conclusion? As we look deeper into both sides of the argument we might just find out that the answer has been under our noses all along.
First off what is Anatomy? Anatomy is the branch of science concerned with the bodily structure of humans, animals, and other living organisms. We’ll begin this paper by comparing the human digestive system to herbivores and carnivores, animals that get their energy and nutrient requirements through the consumption of other organisms being the main source in their diet, to see the contrasting difference between the two polarized groups and see which group humans are the most similar to.
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Digestive System
The digestive system is made up of the GI (gastrointestinal)tract, liver, pancreas, and gallbladder. The GI tract is different hollow organs joined in a long tube from the mouth to the anus. The organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine, and anus. The liver, pancreas, and gallbladder are the solid organs of the digestive system.
The small intestine has three parts. The first part is called the duodenum. The jejunum is in the middle and the ileum is at the end. The large intestine includes the appendix, cecum, colon, and rectum. The appendix is a finger-shaped pouch attached to the cecum, the first part of the large intestine. The colon is next and then the large intestine ends with the rectum. Bacteria in the GI tract helps with digestion and together nerves, hormones, bacteria, blood, and the digestive system organs digest the foods and liquids organisms eat and drink every day. Digestion is important because the body needs nutrients from foods and drinks to work properly and stay healthy. The digestive system breaks nutrients into small parts so that the body can absorb and use them for energy, growth, and cell repair.
Mouth
The start of the digestive process begins at the mouth. From a young age people are told that humans have canines because we are meat-eaters, but the rest of our teeth are flat and our canines are blunt and nothing compared to real omnivores and carnivores. Carnivores and omnivores have large mouths full of sharp teeth with sharp canines, incisors, and molars. Their sharp teeth make it easy to rip through flesh, and since chewing isn’t necessary for carnivores and omnivores, they do not need flat teeth for grinding. Compared to herbivores even their saliva is different. Their saliva does not have digestive enzymes to help the breakdown of carbohydrates since their diet is mostly based on eating protein and fat. Herbivores have smaller mouth full of blunt teeth for chewing. It is important that herbivores chew their food thoroughly so that their bodies can break down the plants they eat more easily. They also have carbohydrate-digesting enzymes in their saliva to further aid in breaking down food before it hits the stomach. Humans have small mouths, blunt incisors(a narrow-edged tooth at the front of the mouth made for cutting) and molars for chewing, and saliva that contains digestive enzymes. Another difference is that a carnivore’s jaw cannot move left and right to grind food, and can only move up and down. A herbivore can move their jaw left and right, automatically like a human.
Stomach
As we move downwards towards the stomach we’ll start to see the differences stack up even more. The stomach receives food from the esophagus and secretes acid and enzymes that digest food. Carnivores and omnivores have simple singular stomachs. Their stomach acidity is much higher than herbivores and has a pH less than/ equal to 1 on the pH scale. The ph scale is a logarithmic scale used to specify acidity. A pH greater than 7 is basic. A pH of 7 is neutral. A pH less than 7 is acidic. Each pH number below 7 is 10 times more acidic than the the next higher value. Herbivores can have simple singular stomachs and multiple stomachs, like a cow for example has four. Their stomach acid is mostly neutral and has a pH level of 4 to 5. Humans have a simple stomach with an acidic of pH 4 to 5 while food is present.
Small Intestine
The small intestine is where nutrients are absorbed in the bodies of animals. The length of the intestine correlates to the specific diet of the animal. Carnivores and omnivores have a short small intestine that is approximately 3 to 6 times their body length. Herbivores have a long small intestine that is approximately 10 to 12 times their body length. Humans have a long small intestine that is roughly 10 to 11 times the length of their body.
Colon
The colon passes through the small intestine, it extracts water and salt from solid wastes before they are eliminated from the body and is the main part of the large intestine. Carnivores and omnivores have short and smooth colons that are not sacculated. Herbivores have long, complex, and sometimes sacculated colons; while humans have long colons that are sacculated.
Liver and Kidneys
Differences can also be found in the liver and kidneys, which are essential for detoxing human bodies. Carnivores and omnivores livers can detoxify vitamin A, which is important for vision, the immune system, and reproduction. Also their kidneys produce highly concentrated u
rine. Herbivore livers can’t detoxify vitamin A, and their kidneys produce less concentrated urine than a carnivores. A human’s liver cannot detoxify vitamin A, and our kidneys produce moderately concentrated urine.
Skin
Carnivores don’t have sweat glands on their skin so they cool themselves off by sweating through their foot pads and by panting. Herbivores sweat through their skin exactly the same as humans.
Through research various studies have also shown the health setbacks of having a high meat diet. In 1984, the Medical Tribune reported studies by Michigan State and other universities about bone density. In the United States they discovered that there was an average of three percent bone loss in male vegetarians compared to male meat-eaters who had an average of seven percent bone loss at age 65. Female vegetarians had an average of 18 percent bone loss when compared to female meat-eaters, who had an average of 35 percent bone loss. The conclusion was that vegetarians had significantly stronger bones than meat eaters. The Inuit people, who live on a very high-protein diet, have the greatest calcium intake of any population and have one of the highest rates of osteoporosis. Clearly the rampant problem with osteoporosis is a byproduct of a nation addicted to meat.
The Bantu women of Africa live on a diet made up of mainly vegetables and free of dairy products. Their average intake of calcium is 250 to 400 mg a day. That amount is way lower than the 800 mg. recommended by the RDA. The women give birth to as many as ten babies during their life, with each child being breastfed for ten months. Even though childbirth can causes an intense calcium decrease, osteoporosis is unknown to these people. When Bantu women migrate to the city and begin to partake in a protein-rich diet, osteoporosis and other diseases threaten their health.
Omnivores
Based on the information above it seems that humans are more similar to herbivores than carnivores. However we still haven’t compared humans and omnivores anatomies yet. Since omnivores eat plants and animals it would be assumed that omnivores have anatomical features that help prepare them for that action. The evolutionary theory explains that a carnivore’s gut structure is way more simple than a herbivores gut because of their(herbivores) adaptations. Basically saying that an omnivore might just be a carnivore with GI tract adaptations,that allow them to sustain the diet of a herbivore.
This is the same circumstance that we find bears and other members of canine family in since bears are classified as carnivores but are classic anatomical omnivores. Even though they eat some animals for food, they are mainly herbivorous because 70-80% of their diet is usually made up of plant foods. The one exception of this is the Polar bear because they live in the arctic were there is hardly any vegetation and they’re limited to eat seal blubber as their primary source of food. Bears can not digest fibrous vegetation well, and therefore, are highly selective feeders. A regular bears diet is typically dominated by food like grasses, flowers, nuts, mushrooms, honey and berries. Scientists believe that the reason bears hibernate is because their main food, which is vegetation, is not available during the winter season. While Polar bears(the outliers) hibernate during the summer months when seals are unavailable.
In general, bears show anatomical features that matches with a carnivorous diet. The small intestine is short (less than five times body length) like carnivores, and the colon is simple, smooth and short. The most prominent adaptation to an herbivorous diet in bears (and other “anatomical” omnivores) is the modification of their teeth. Bears retain the peg-like incisors, large canines and shearing premolars of a carnivore; but the molars have become squared with rounded cusps for crushing and grinding. However bears do not have the flattened, blunt nails like most herbivores and retain the pointed claws of a carnivore.
An animal that kills and eats prey must have the physical attributes that would make hunting more effective. Since bears include meat in their diet, they have to retain the physical attributes that help them catch and kill their prey. Explaining why, bears have a jaw structure, that lets them develop and apply the force necessary to kill and dismember prey even though the majority of their diet is composed of plant foods. Although an herbivore-style jaw is a way more effective for grinding vegetation and would also allow bears to take advantage of a wider range of plant foods in their diet, it is an extremely more weaker joint than the carnivore style joint. The herbivore-style jaw can be more easily dislocated and definitely would not hold up against the stress of overpowering prey and crushing bones. In the wild, an animal with a dislocated jaw would either soon starve to death or be eaten by something else and would, therefore, be selected against. A given species cannot adopt the weaker but more mobile and efficient herbivore-style joint until it has committed to an essentially plant-food diet test it risk jaw dislocation, death and ultimately, extinction.
Counter Argument
Even with this information being out in the public there are still people who believe that humans are omnivores and that without humans eating meat we wouldn’t have been able to advance and evolve to the people we are today. It’s said that Our earliest ancestors ate their food raw — fruit, leaves, and nuts. This type of diet is not high in calories so they had to eat a lot and needed a big gut to digest all of it. However having a big gut was a disadvantage because as anthropologist Leslie Aiello explained “You can’t have a big gut and a big brain”. Since the stomach took so much energy there wasn’t anything left over for the brain until our ancestors discovered meat.
Leslie states that “What we think is that this dietary change around 2.3 million years ago was one of the major significant factors in the evolution of our own species,”. During that period is when cut marks on animal bones first appeared. It was not the tooth marks of another animal, but cuts that were only capable of being made by sharp tools. That was one of the first signs of our earlier ancestors converting into meat eaters. Leslie’s claims her favorite clue to discover was tapeworms. She explained that the closest relative of human tapeworms are tapeworms that are found in African hyenas and wild dogs. So during sometime in our evolution we were sharing saliva with hyenas and wild dogs, most likely when we scavenged for meat on the same animal carcasses.
Meat is filled with lots of fats and calories so as we began to continually eat it our brains got a huge boost of energy that wasn’t going to our guts anymore. This led to our guts shrinking and our bodies could use the remaining energy to make a brains bigger and stronger. This change in diet made our ancestors smarter, which led to them being smart enough to make better tools and other changes. Leslie says “If you look in your dog’s mouth and cat’s mouth, and open up your own mouth, our teeth are quite different,”. “What allows us to do what a cat or dog can do are tools.”
Unlike other predators tools made it so we didn’t need our own sharp teeth. They were like external teeth for humans and even made dealing with vegetable matter easier. But adding raw meat to our diet doesn’t tell the whole food story, according to anthropologist Richard Wrangham. Wrangham explains that even after we started eating meat, raw food just didn’t pack the energy to build the big-brained, small-toothed modern human. He cites some research that showed that people on a raw food diet that included meat and oil had lost a lot of weight. Alot of the participants said they felt better, while also mentioning that they experienced extremely low energy. Even half of the women were reported to have stopped menstruating during the experiment. It’s not like raw food isn’t full of nutrition but it’s harder for the body to get the nutrition.
Wrangham uses raw turnips as an example. “They’ve got a tremendous amount of caloric energy in them. The problem is that it’s in the form of starch, which unless you cook it, does not give you very much.” Then there is also the fact that the action of chewing takes up energy.
One solution would have been pounding the food, especially meat. “If our ancestors had used stones to mash the meat then it would have reduced the difficulty they would have had in digesting it.”However pounding is not as good as cooking and cooking is what Wrangham really thinks changed our bodies into the ones we have today. It started with someone discovering fire(which no one knows when this happened)and then someone else deciding to throw some food on the fire which led to the joys of eating cooked food that was pathogen free.By cooking it led to the meat changing itself because it broke up the long protein chains, and that made them easier for stomach enzymes to digest. “The second thing is very clear,” Wrangham adds, “and that is the muscle, which is made of protein, is wrapped up like a sausage in a skin, and the skin is collagen, connective tissue. And that collagen is very hard to digest. But if you heat it, it turns to jelly.” Softening food makes it become more digestible and after you’ve finished cooking you’ll get more energy out of the food.
Cooking has been found to damage some good things in raw food, like vitamins. But Wrangham argues that what’s gained by cooking far outweighs the losses.Wrangham also explains that cooking has led to different behavioral patterns of humans like encouraging people to share labor, bring families and communities together at the end of the day, and encouraged conversation and storytelling. But at the end of the day he believes what really made us human was our big brains which were products of eating cooked meat.
There is also a study that supports the idea of meat aiding humans in our becoming smarter. The researchers studied 67 different animal species(including humans)and they found that all the animals stopped nursing when their brains hit a certain stage of development, regardless of diet. All the meat-eaters, including ferrets, killer whales, and humans, reached that point of brain development earlier than herbivores or omnivores. In the study humans were classified as carnivores based on the percentage of meat in a regular diet of a human. These results supports the hypothesis that meat-eating may have had a major evolutionary effect on human development. Appearing to confirm that carnivory has a specific and quantifiable impact on human development and explains why we weans so much earlier than the great apes. Also, the researchers concluded,that the big difference in breast-feeding times between humans and other primates is because of the better nutrition provided to both mothers and babies by meat consumption.
