We often classify animals according to what they eat, as a sort of shorthand for describing what kind of animal they are. The three basic classifications we use are herbivore (plant eating), carnivore (meat eating), and omnivore (will eat both plants and meats). With each category are sub-categories that are more specific: for example, within the herbivore category are the frugivores, which eat only fruit, and folivores, which eat only leaves (not grasses). Within the carnivore section are various levels of meat-eating. Animals which need meat in order to survive, but can also consume plant matter (although they get very little nutrients from it) are called obligate carnivores. Animals that can *only* consume meat are called hypercarnivores. Interestingly, the hypercarnivore classification does not include most of the major predatory animals – hypercarnivores are usually birds of prey and water-dwelling species, such as certain fish, snakes, dolphins, and octopi.

The last category is the broadest, and the one to which man belongs: omnivores. Many people mistakenly think that omnivore means that the animal will eat anything. But what it really means is that the animal is capable of extracting nutrition from both plant and animal matter. A common example of an omnivore would be the raccoon. Raccoons are very successful at adapting to living with humans, in part because they can adapt to eating human foods – more specifically, in urban areas they usually eat trash and/or pet food. But in areas away from humans, raccoons can be very picky about their diet. They will catch and eat small fish and frogs, and the also like to eat insects, worms, and snails. All these are a form of meat. Raccoons also eat plants, roots, seeds and fruit, which are all plant matter. But other omnivores are not so wide-ranging in their abilities to extract nutrients from different sources. Humans, for example, do very poorly at extracting anything useful from cellulose plant material, like bark, wood, and grass. We also do not get very much nutritional value from eating insects. So being omnivorous does not mean that an animal can survive on a diet of anything – it just means that the animal is capable digesting both meat and plants, to a greater or lesser degree.

There is very frequently overlap between the carnivore and omnivore category. Bears are a particular problem. Technically they belong to the order Carnivora, but they are largely omnivorous. The polar bear and the sloth bear (which eats only termites) are two true obligate carnivores in the bear family. But, due to details of their teeth and their ancestry, bears remain in the carnivore category in terms of their taxonomy, but are considered omnivorous in the common sense of the word. In the same vein, squirrels, which we think of as primarily eating fruit, seeds, and vegetables, also eat bird eggs (considered meat), bird fledglings, insects, and sometimes small reptiles. So while they technically fall into the herbivore category, their actual eating habits are omnivorous.

We can see that these three categories are flexible in the common usage. In taxonomic usage, they refer not only to what the animal has been observed eating, but to internal organs, skeletal and tooth structure, and ancestry. This can be confusing to the non-scientist, but neither usage is ‘wrong’. The ‘correct’ assignment of an animal to a particular category depends on the context, and for most people the context is not a strictly science-based one. Therefore, in common usage it is not incorrect to say that bears are omnivores, or that squirrels are herbivores.

The question that plagues many humans is, are humans omnivores or herbivores? The scientific answer, based on dentition and internal structures, is that humans are omnivores. But remember that omnivorous does not mean ‘will eat anything’. Omnivores are capable of digesting plant material and meat. But that doesn’t mean that they need both plant and animal matter in their diet. Many omnivores eat a mostly plant-based diet, while many lean more towards the carnivorous side. Many have diets that change according to the season, or their location. Humans, as omnivores, can choose if they want to eat a plant-based diet, a meat-based diet, or something in between. The omnivore category does not limit us in terms of diet - it gives us the broadest possible choice.