|MadSci Network: Other|
Are humans vegetarians or omnivores? Those terms are not strict biological designations, and so the question needs to be rephrased a bit before it can be answered. The confusion stems from the use of the word "carnivore" to mean "meat eater" - instead the word carnivorous should be used. To be biologically strict here, a carnivore is an order of mammal (recognized by the presence of the carnassial tooth, among other things) that includes cats (felids), dogs (canids), bears (ursids), and a number of other mammalian families. Carnivores are not strictly meat eaters - most will eat some type of plants as a part (sometimes even the main part) of their diet. The term "vegetarian" is strictly a human construct. Vegetarians shun animal products for food, usually for religious or ethical reasons. Even still, there are degrees of vegetarian. Some vegetarians will never consciously eat any food that comes from an animal. Other will consume dairy products (an animal food even though it isn't meat). Others will allow themselves to eat eggs (the pre-chicken, so to speak), or fish. Vegetarianism is more of a dietary philosophy then an ecological food preference, so it's hard to speak of it in biological terms. Biologists rarely (never in my experience) categorize non-carnivorous animals into one "plant eating" group. That is because different dietary specializations are required to eat different types of plants. Thus, you will hear of herbivores (specialized to eat shoots and growing tips), folivores (specialized to eat leaves) and frugivores (specialized to eat fruit) among other adaptations. Even within these broad groupings there are further specializations, such as grazers that eat grass and browsers that eat shrubs (both are types of herbivore). And even among the "plant eating" animals there is no animal that I am aware of that will not consume some type of animal protein when given the opportunity. An omnivore is an animal that will draw its food from all aspects of the ecosystem (plants, animals - whatever). As I've already pointed out, you could claim that nearly every animal is omnivorous since a purely meat eater or purely plant eater is very rare. Nonetheless, you can look at the animal's anatomy to look at how they are adapted to process food. First you can look at the teeth. Molars are broad flat teeth that are useful in grinding up tough fibrous material - such as plants. Animals that are primarily plant eaters have very large molars with six pairs (three uppers and three lowers) on each side. Animals that do not specialize in eating plants tend to have a reduced number of molars. Humans are equipped with six pairs of molars. Although they are not very large, this would suggest that humans have the ability to process fibrous plant food. Premolars (bicuspids) are the slicing teeth. Mammals originally had eight pairs of premolars, although most mammals alive today have fewer. Premolars are the primary teeth used by meat eating specialists, and are frequently missing in animals that specialize in plant foods. Humans have four pairs of premolars, which suggests that humans have the ability to process animal food. Incisors are grasping teeth, that change shape depending upon how they are used. The broad flat surfaces of human incisors is most associated with animals that specialize in eating fruit. So, if we just look at our teeth - humans are clearly built to be omnivorous. But, of course there is more data. We can look at how nutrients are processes and absorbed in the body. Meat and fruit are high quality foods that are not difficult to assimilate. Animals that specialize in these types of food tend to have a short digestive tract, with a very short large intestine. Plant foods can be nutritious, but take longer to absorb. Therefore, animals that specialize in plant eating tend to have long and elaborate digestive tracts. Humans are clearly intermediate here. We have a long large intestine (more common in plant eaters), but we lack the elaborations that would allow us to digest and assimilate nutrients from high fiber plant foods (such as grass or leaves). So, again, the human digestive tract can be used to argue that we are omnivorous. Finally, you need to look at nutritional requirements. There are some B-complex vitamins that are available only by eating other animals. The human body requires this nutrient, but does not synthesize it the way some other animals do. Therefore, if humans truly ate no animal foods, and had no artificial vitamin supplements, they would sicken and die. In nature, there are no true "human vegetarians." Humans are omnivores. The order of mammals that includes humans (the primates) are all omnivores. To be sure, the modern American diet includes a lot more meat than is healthy. And the human animal can be very healthy by being a lot more vegetarian. But to never eat meat is both unnatural and unhealthy. Finally, you ask about my credentials to answer this question. Well, I am employed as an anatomy professor (and am therefore a specialist in human anatomy). I teach at a college that specializes in training health care workers (so I am familiar with issues of human health an nutrition). Finally, I earned by Ph.D. in Physical Anthropology (which sort of makes me an expert in how humans adapt both biologically and culturally to the environment). Some References relevant to this questions: Harding, RSO & Teleki, G (1981) Omnivorous Primates. Columbia University Press: New York. Romer, AS & Parsons, TS (1986) The Vertebrate Body. Saunders College Publishing: New York Oxnard, C. (1987) Fossils, Teeth and Sex. University of Washington Press: Seattle
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