Are Humans Omnivores? by John Coleman - HTML preview

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It is not unusual to hear the claim that humans are "omnivores", even authoritative text books and research papers use this term. Unfortunately the meaning of this term is somewhat vague. On the one hand, the term omnivore can simply be used to describe animals that eat plant or animal foods, and on the other, it may be used to infer that an animal is biologically adapted to consume both plant and animal foods, and perhaps, that it is supposed to do so. A broader, and perhaps more appropriate definition of an omnivore, would refer to animals than can consume all kinds of food. This is because omni derives from the latin omnis meaning all.

Therefore, in common use, the term omnivore may be used to describe both a) what an animal does and b) what an animal is. Clearly humans are omnivores in the sense that they do eat both plant and animal foods. As an example of the contrast between is and does, cattle consume animal remains in contemporary farming practices, yet cattle are still considered to be herbivores - though they could be said to be omnivores in that they can eat an omnivorous diet. This article addresses the suggestion that humans are biologically omnivores, because this is what people infer when they say "humans are omnivores".

Establishing a testable criteria for omnivorism

There seems to be no scientific procedure by which to establish that an animal is biologically omnivorous, and it is because of this that debate is possible. A reasonable proposition is an omnivore should be able to make both plant and animal foods a significant part of the diet without detrimental effects. To really make a convincing case for an animal being omnivorous we would like to see both biological adaptations to plant and animal foods. Without testable truth claims and concrete evidence, it is spurious to use the term omnivore. Even so, there is quite clear biological evidence, as we shall see, that could confirm that a species is adapted to a diet of both plant and animal foods.

This article is the result of a broad study of scientific evidence to identify human dietary adaptations, and presents data which together suggest that humans meet the criteria for being a specialist frugivore, and furthermore we see no compelling evidence that humans meet the omnivorous criteria set out above. Specialist frugivores could be defined as animals that have specialised adaptation to a diet high in fruit. As with other frugivorous animals, this classification is general, and would not necessarily exclude consumption of other kinds of plant matter, i.e. non-fruit plant foods, or even animal matter as lesser constituents of the diet. A specialist frugivore is therefore to be seen as distinct from an omnivore. An omnivore should be capable of eating significant amounts of animal matter, without detrimental effects, and would have clear adaptations to such a diet in order to make the claim convincing.

In this article I assume that the dog or pig is an archetype for the omnivore, because we know they well tolerate both plant and animal matter as a regular and significant part of their diet, and because they are well known to eat just about anything that is edible. However, many non-human primates include significant amounts of animal matter in their diet, and so might make a better comparison. Unfortunately, little is known and documented about how well the great apes, the group of animals to which humans are most closely biologically related, tolerate significant intakes of animal matter, and furthermore, primates seem far more selective with their food choices than the archetype omnivores suggested.

There are some confounding issues with studying primates. The non-human primates, like humans, are capable of learning new eating behaviours and forming localised food cultures, such that it may not be easy to generalise about their diets. Therefore, when we see one group of a species of primates consuming a diet that is mostly plant based, and another group of the same species that is consuming much more animal products, it doesn’t follow that the primate is omnivorous by biological adaptation - we may have a case of does an omnivore diet, rather than is an omnivore biologically. This we discover exactly the same issues that occurs in calling humans omnivores.