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(Comparative Anatomy and Physiology Brought Up to Date--continued, Part 2A)

Looking at Ape Diets--Myths, Realities,
and Rationalizations

Dietary Classifications & Word Gamesmanship

Dietary categories are not strict in nature

A good place to begin our exploration of the topic of natural diet as it relates to morphology (anatomical form) is with dietary classifications. In nature, dietary classifications are rarely strict. Herbivores (folivores) routinely consume significant amounts of insects (animal matter) on the leaves they eat. Some folivores--e.g., gorillas, including the mountain gorilla--may deliberately eat insects. Carnivores may seek out and deliberately consume grasses and other plant matter on occasion, and they may consume the stomach contents (vegetation) of herbivores they prey on. Frugivores normally eat some leaves and/or animal matter in addition to their primary food of fruit.

Extreme diets--diets that are 100% of a specific food or narrow food category--are not very common in nature. In sharp contrast to the spectrum of broad-based diets that one finds in nature, however, one can easily find dietary advocates promoting (human) diets that have a relatively narrow basis: 100% vegan, 100% raw vegan, 75+% fruit, and so on.

High variability of primate diets

Primates may frequently switch dietary categories

When discussing dietary categories, it is very easy to forget that extremes are rare in nature, and instead focus exclusively on the central food (or food category) consumed, and ignore the other foods consumed. If one classifies chimps as frugivores, it is easy to forget that they also consume smaller but nutritionally significant quantities of leaves and animal foods (both invertebrates--insects--and vertebrates, or other mammals). The fact that humans are primates is also relevant, for primate diets tend to be highly variable on a month-to-month basis in the wild. Chapman and Chapman [1990] reviewed 46 long-term studies of wild primates, with attention on monthly variations in diet. They noted (pp. 121, 126):

...primates do not consistently combine the same kinds of foods in their diets, as many past characterizations would suggest, but rather, that they often switch between diet categories (e.g., fruit, insects, etc.)... Our review of primate diets on a monthly temporal scale suggests that primates do not always consistently include the same kinds of foods in their diets. Instead, primate populations frequently switch between diet categories.

Animal food consumption common

Harding [1981], noting the widespread reports of predatory behavior and meat consumption by non-human primates, makes the interesting comment (p. 191; my explanatory comments are in brackets [ ] below):

It is now clear that several primate populations make regular and substantial use of precisely the type of food [animal flesh] which the early theories described as instrumental in the emergence of the hominids.

If the diets of these particular nonhuman primates are more broadly based than we had thought, then how accurate is it to characterize contemporary primate diets in general as "vegetarian"?... As Teleki points out (1975: 127ff.), such terms are first used as shorthand references to a particular dietary specialization but then gradually become inclusive descriptions of an animal's entire diet. Essential elements of the diet are ignored, and the result is a generally misleading impression of what a group or population actually eats. As this article shows, diversity rather than specialization is typical of primate diets.

Drawing boundaries between diet categories is non-trivial

As mentioned above, extreme diets are rare in nature. Instead, there is a spectrum of diets, and drawing lines or boundaries in the multi-dimensional dietary spectrum to distinguish between, say, frugivores and faunivores [faunivore = meat-eater] is a non-trivial problem. The reality that primates may frequently switch dietary categories makes the situation even more complicated.

Chapman and Chapman [1990, p. 123], citing Mackinnon [1974, 1977], report that in one month, orangutan diet in Sumatra was frugivorous (90% fruit by feeding time), but the same population at a different time was folivorous (75% leaves by feeding time). One month a frugivore, later a folivore: how to classify? Additional evidence on the variability of orangutan diets is given in Knott [1998, p. 40]. Further, there is even some academic disagreement over the definition and use of the term "omnivore." These topics are addressed later in this paper.

Common vs. scientific diet category terms

Use of the cultural terms "vegan" and "fruitarian" versus "folivore" and "frugivore"

Another relevant aspect of dietary classifications: The terms vegan, fruitarian, and vegetarian are all human cultural terms, and are used, at least by most dietary advocates, with narrow definitions. One may hear an advocate claiming that "apes are vegans," then later the same advocate might criticize others for using the same terminology--i.e., "apes are NOT vegans"; the specific criticism being that a biological term is more appropriate (e.g., folivore, frugivore, faunivore).

In this article, a primary objective is to communicate concepts clearly and accurately but without undue complexity. Hence, since most readers would generally understand that the phrase "apes are NOT vegans" means that a human who eats the same diet as the apes would not qualify as a vegan, here we won't worry about the technical terms unless/until they are necessary to assist the reader in understanding the material. (Technical terms are used extensively in certain sections of this paper, but will be defined as we go along.)

To Summarize:

The Evidence of Ape/Primate Diets

Preface. A comparison of humans vs. allegedly "vegetarian" anthropoid apes is frequently a part of comparative anatomy/physiology "proofs" that assert humans are natural vegetarians. ("Anthropoid" means the most human-like apes in the "great apes" family, which includes the chimpanzee, gorilla, and orangutan.) However, as knowledge of the actual diet of wild primates/anthropoid apes (from field observation studies) increases, the reality that most primates/apes include some animal foods (even if only insects) in their normal, natural diet is becoming better known. As a result of this, the myth of the "vegetarian ape" is slowly slipping away.

Ape diets, with emphasis on chimpanzees, are summarized in the article "Setting the Scientific Record Straight on Humanity's Evolutionary Prehistoric Diet and Ape Diets" on this site. Additionally, some of the rationalizations by dietary advocates that have been advanced as part of attempts to preserve the myth of "vegetarian apes" are discussed in "Selected Myths of Raw Foods." The current section serves primarily to supplement the above articles, and to address other, newer rationalizations and misinformation promoted by dietary advocates who stubbornly cling to the "apes are vegetarians" myth.

Claims Made in Fit Food for Humanity

The booklet Fit Food for Humanity [Natural Hygiene Press 1982] makes what could be considered the classical comparative argument: humans vs. anthropoid apes. The booklet argues that:

The booklet then reaches the conclusion that humans are natural vegetarians, i.e., that the vegetarian diet is the (only) diet in accord with human anatomy. However, the line of argument given above is incorrect and logically insufficient to establish the claimed result. The structural problems in the above type of argument are addressed in later sections. This section will focus specifically on the issue of ape diets.

"Vegetarian" apes: a misconception of the past

First, as mentioned above, the idea that apes (or primates in general) are strict vegetarians in the normal human sense of the word is a misconception of the past. This point is clarified in Sussman [1987, pp. 166, 168]:

In fact, most species of primate are omnivorous (see Harding [1981]) and omnivory should be considered an evolutionarily conservative and generalized trait among primates. Primates evolved from insectivores....

Thus, omnivorous primates are mainly frugivorous and, depending upon body size, obtain most of their protein from insects and leaves. In all large, omnivorous, nonhuman primates, animal protein is a very small but presumably necessary component of the diet.

In the above, the term omnivore has the usual definition; e.g., from Milton [1987, p. 93]: "By definition, an omnivore is any animal that takes food from more than one trophic level. Most mammals are in fact omnivorous...". ["Trophic" refers to the different levels of the food chain.] Note that some experts use a different, more precise definition for the term omnivore, and disagree that mammals are omnivores--instead they suggest using the term faunivore for animals that regularly include fauna (other animals) in their diet.

Insect food

Regarding consumption of animal foods by primates, Hamilton and Busse [1978, p. 761] note:

Many primate species once considered herbivorous are now known to expand the animal-matter portion of their diet to high levels when it is possible to do so...

Insect food is the predominant animal matter resource for primates. Insects are eaten by all extant apes, i.e., chimpanzees (e.g., Lawick-Goodall 1968), orang-utans (Gladikas-Brindamour1), gorillas (Fossey2), gibbons (Chivers 1972, R.L. Tilson3), and the siamang (Chivers 1972). The amount of insect matter in most primate diets is small, but may expand to more than 90% of the diet when insects are abundant and easily captured...

Preference for animal matter seems confirmed.

Note that the footnote numbers in the quote above refer only to Hamilton and Busse [1978].

Rationalizations about Dietary Deviations among Primates

Fit Food for Humanity does include notes on "Dietary Deviations Among the Primates" (pp. 11-12). It is interesting to note that most (but not all) of the references cited therein are encyclopedia entries--which usually do not reflect the latest research. The response in Fit Food for Humanity to the information that anthropoid apes are not strict vegetarians could be characterized as reliance on outdated information, rationalizations, and hand-waving.

Let's review some of the claims. ("FFH" is used as an abbreviation for Fit Food for Humanity in the material below.)

FFH: Gorillas are total vegetarians.

REPLY/COMMENTS: Both lowland and mountain gorillas consume insects, deliberately and indirectly, that is, on the vegetation they consume. The above quote from Hamilton and Busse [1978] cites Fossey (personal communication) regarding insect consumption by mountain gorillas. Tutin and Fernandez [1992] report consumption of insects by lowland gorillas in the Lope Reserve, Gabon: termites (whose remains were contained in 27.4% of gorilla feces) and weaver ants. Note that both insects mentioned are social insects; the consumption of social insects is efficient, as their concentration in nests allows easy harvesting of significant quantities. Of further interest here is the information that termites are known to contain significant quantities of vitamin B-12; see Wakayama et al. [1984] for details. Insectivory by mountain gorillas is discussed further later in this section.

FFH: Orangutans consume 2% insects; from p. 11: "the 2% digression may be seen as incidental and insignificant."

REPLY/COMMENTS: The quote from FFH does not specify whether the 2% is by weight or feeding time. Due to the difficulties in estimating weights of foods consumed, the 2% figure is probably by feeding time. Galdikas and Teleki [1981] report that orangutans at Tanjung Puting Reserve in Indonesia consumed 4% fauna (insects, eggs, meat) by feeding time. Kortlandt [1984] reports that (p. 133), "orang-utans eat honey, insects and, occasionally, bird's eggs, but no vertebrates."

For photos of a wild orangutan eating insects, see Knott [1998], p. 42; and for a photo of a wild orangutan eating a vertebrate--a rare event--see Knott [1998], p. 54.

The claim that insect consumption by orangutans is "insignificant" is clearly an unproven assumption. Insects and other animal foods are nutrient-dense foods: they supply far more calories and nutrients per gram of edible portion than the same weight of most of the plant foods commonly consumed (i.e., fruits other than oily fruits, and leaves).

FFH: The principal rationalizations given for termite and meat-eating by the chimps of Gombe Preserve are:

FFH then implies (assumes) that the behavior of the chimps of Gombe is in imitation of human behavior. Other writers (elsewhere, not in FFH) suggest that chimps eat meat in imitation of baboons.

REPLY/COMMENTS: The reality is that predation on vertebrates by chimpanzees is widespread throughout tropical Africa. Regarding chimpanzee predation, Teleki [1981, p. 305] reports that:

Moreover, predatory behavior involving vertebrate prey has now been recorded at all major study sites in equatorial Africa, from Uganda and Tanzania to Sierra Leone and Senegal. I expect that the known geographical distribution of predatory behavior will continue to expand as new chimpanzee projects are launched, though it is probable that some populations practice this behavior little or not at all, while others do so regularly and systematically (Teleki, 1975).

Note in the above remark that predation by chimps has been found at all major study sites, although it is possible that some groups of chimps hunt rarely, or not at all.

Over and above the reality that predation and meat-eating by chimps is widespread, the claim that chimps do so in imitation of humans or baboons is both unproven and dubious. Chimps have lived in proximity to both humans and baboons for approximately 2-2.5 million years. This alone suggests that sufficient time has elapsed, in evolutionary terms, for chimps to adapt to such allegedly "imitation" behavior. Once evolutionary adaptation occurs, the "imitation" behavior would no longer be an imitation (supposing it were that, in some hazily conceived past)--it is natural. This reasoning suggests that the "imitation" argument is dubious at best. Another problem with the "imitation" argument is that imitative learning in captive chimps is common, but in wild chimpanzees it is rare; see Boesch and Tomasello [1998] for discussion on this point.

Chimp/Baboon Interaction. The interaction between baboons and chimps is quite interesting and serves to illuminate the shallow nature of the "imitation" argument. Teleki [1981, pp. 330-331] comments on:

...the anomalous nature of an interspecific relationship that includes play with baboons, consumption of baboons, and competition with baboons for at least one kind of prey...

[T]he Gombe chimpanzees removed 8% of the local baboon population in 1968-1969 (Teleki, 1973a) and 8-13% of the local colobus population in 1973-1974 (Busse, 1977). How is it possible, then, that the primates serving as prey to chimpanzees in Gombe National Park, and possibly also at other sites, have not developed more successful defensive tactics? Any answer other than the proposition that chimpanzees have only recently acquired predatory inclinations, for which there is no supportive evidence at all (Teleki, 1973a), would be welcome."

Note: The above quote is included to specifically inform readers that there is no evidence that predation by chimps is a "new" behavior, and that there is extensive, complex, baboon/chimp interaction.

Insect Consumption by Chimps is Universal. Kortlandt [1984] also discusses insect consumption by chimps (p. 133):

Chimpanzees, on the other hand, spend a remarkable amount of time, mental effort and tool use on searching out insects and feeding on them in every place where they have been intensively studied. Hladik and Viroben (1974) have shown that this insect food is nutritionally important in order to compensate for a deficiency of certain amino acids in the plant foods, even in the rich environment of the Gabon rain-forest.


(Ape Diets: Myths, Realities, and Rationalizations, cont.)

Return to beginning of article



GO TO PART 1 - Brief Overview: What is the Relevance of Comparative Anatomical and Physiological "Proofs"?

GO TO PART 2 - Looking at Ape Diets: Myths, Realities, and Rationalizations

GO TO PART 3 - The Fossil-Record Evidence about Human Diet

GO TO PART 4 - Intelligence, Evolution of the Human Brain, and Diet

GO TO PART 5 - Limitations on Comparative Dietary Proofs

GO TO PART 6 - What Comparative Anatomy Does and Doesn't Tell Us about Human Diet

GO TO PART 7 - Insights about Human Nutrition & Digestion from Comparative Physiology

GO TO PART 8 - Further Issues in the Debate over Omnivorous vs. Vegetarian Diets

GO TO PART 9 - Conclusions: The End, or The Beginning of a New Approach to Your Diet?

Back to Research-Based Appraisals of Alternative Diet Lore

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