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

Other "Apes Are Vegetarians" Claims

Outdated quote from Stevens and Hume [1995]

On occasion, one sees the following quote from Stevens and Hume [1995, p. 76] cited in support of the "apes are vegetarians" myth:

The gorilla, chimpanzee, and orangutan are generally considered to be strict herbivores, although there is evidence that chimpanzees may hunt and eat termites and smaller monkeys (van Lawick-Goodall 1968).

The Stevens and Hume [1995] reference (a book, Comparative Physiology of the Vertebrate Digestive System) is, in general, a good reference. However, the specific quote above is clearly outdated. (In a later section, we will discuss another quote from Stevens and Hume [1995] that is also misused by certain dietary advocates.)

Less predominant foods often "assumed away" by fiat. We have already (briefly) discussed insect consumption by gorillas and orangutans. Though insects are a small component of their diet, we note the following:

Given that the Stevens and Hume [1995] quote mentions Jane van Lawick-Goodall [1968], the dated nature of the quote is easily illustrated by van Lawick-Goodall [1971] herself, where she reports that the chimps of Gombe consume a wide array of insects, bird's eggs, and chicks, and the following vertebrate prey (from pp. 282-283):

Most common prey animals are the young of bushbucks (Tragelaphus scriptus), bushpigs (Potamochoerus porcus) and baboons (Papio anubis), and young or adult red colobus monkeys (Colobus badius). Occasionally the chimpanzees may catch a redtail monkey (Cercopithecus ascanius) or a blue monkey (Cercopithecus mitis).

As the information has begun to spread within the raw vegan community that ape diets include some animal foods, even if only a limited amount of insects, certain raw vegan advocates have reacted with brand-new rationalizations and claims, which we examine next.

Chimp predation is supposedly "an error" or "maladaptive"

One rationalization made is that the chimps eating meat are acting "in error" or are "perverted." The logical fallacies of such crank/bogus claims are discussed briefly in Selected Myths of Raw Foods. (One wonders what irrational beliefs drive those fruitarian extremists who appear to think they know more about chimp diet than the chimps themselves?) Yet another rationalization promoted by fruitarian extremists is that meat-eating by chimps is "maladaptive," i.e., anti-evolution. Those who promote this claim have no credible evidence to support their views, and they conveniently ignore that the consumption of insects--an animal food--is apparently universal (or nearly universal) among adult chimpanzees. The comments of Kortlandt [1984, p. 134] address the above rationalizations:

We should consider here that hunting and killing vertebrates involves health hazards resulting from injury, and that eating meat implies the risks of parasitic and contagious diseases. Such behavior, therefore, strongly indicates certain deficiencies in the composition of the available vegetarian diet.... Similarly, the preference for eating the brain of the victim suggests a lack of lipids and possibly other components in the diet.

Meet the mountain gorilla, the new "model ape"

Recently, some new claims have surfaced regarding the mountain gorilla:

The new claims cited above are interesting. While there have been claims in the alternative diet movement in the somewhat distant past emphasizing gorillas as models of fruitarian diet (see Dinshah [1976-1977], for example), advocates since then have tended to concentrate more on the chimpanzee. Now, however, after years of using chimps as the "model vegetarian ape," such advocates are changing course. The above claims appear to attempt once again to designate the mountain gorilla as the NEW "model vegetarian ape," and thereby divert attention from the (now more widely acknowledged) news of chimps who eat meat and termites.

Examining the Claims about Gorillas

DNA analysis of hominoids

Let's now examine the above claims. The claim that mountain gorillas are the "closest" to humans is simply false, and DNA evidence is available for analysis here. Sibley and Ahlquist [1984] analyzed the DNA sequences of hominoid primates: humans, chimpanzees (including bonobos), gorillas, orangutans, etc. (Note: "Hominoid" is a grouping that includes both the "anthropoid apes"--also known as the "great apes"--plus humans as one related family of primates based on their shared "human-like" traits.) Their research produced a matrix of Delta T(50)H values--a distance function that measures differences between DNA sequences. The distances they found (from Sibley and Ahlquist [1984, p. 9]) are:


Genetic Distance (Delta)

Human / Chimpanzee


Human / Bonobo


Human / Gorilla


Human / Orangutan


Note that the human/chimp and human/bonobo DNA distances are lower numbers than the human/gorilla DNA distance. Hence we observe that chimps and bonobos are "closer" to humans than gorillas are.

Sibley and Ahlquist expanded their 1984 research with similar results; see Sibley and Ahlquist [1987] for details (the paper also includes a review of related research papers). Felsenstein [1987] provides even more insight into the Sibley and Ahlquist research via a statistical analysis of their data set.

Similar results come from earlier research. Goodman [1975] compared hemoglobin amino-acid chains, and computed amino-acid distances for humans versus selected non-human primates. Goodman's methods were slightly different but the results were similar to the above: chimps are "closer" to humans than gorillas are. (See Goodman [1975, p. 224] for the amino-acid distance values.)

Mountain gorillas eat insects

Beyond the erroneous genetic-distance assertion, the claim that mountain gorillas are strict vegans (in the normal human sense) is incorrect as well. Mountain gorillas are folivores, and their predominant food is leaves; however, at least some mountain gorillas deliberately consume insects. Watts [1989] observed mountain gorillas feeding on driver ants in the Virunga Volcanoes region of Rwanda and Zaire.

Deliberate consumption. Watts [1989 (pp. 121, 123)] notes:

Not all gorillas in the Virungas population eat ants...

Gorillas become very excited during ant-eating sessions, and even silverbacks who are not eating ants sometimes give chest-beating displays...

Some mountain gorillas eat ants with striking eagerness and excitement, and the rate of food intake per unit feeding time is higher than for other means of insectivory (Harcourt and Harcourt, 1984). But ant-eating is so rare that, like searches for egg cases inside dead plant stems (ibid), it probably is not nutritionally important. It may differ in this respect from termite-eating by lowland gorillas in Gabon (Tutin and Fernandez, 1983)...

Fossey and Harcourt [1977] report that mountain gorillas in Rwanda consume grubs.

Inadvertent consumption more important? Harcourt and Harcourt [1984] analyzed inadvertent insect consumption by gorillas in the Virunga Volcanoes area. They note (pp. 231-232):

...adding all sources of invertebrate material produces a daily consumption of about 2g of animal matter per adult gorilla...

Clearly gorillas inadvertently eat many invertebrates during their daily vegetarian diet, and far more than they eat deliberately...

[T]he daily 2g of invertebrates makes up just 0.01% of the intake...

When invertebrates occur at high concentration in the environment they are deliberately sought by the gorillas, and not a little time sometimes expended in their procurement...

Invertebrate consumption could be necessary to satisfy trace element requirements in a species with a near-monotypic vegetarian diet [Wise, 1982].

Harcourt and Harcourt [1984] also suggest that deliberate insect consumption by gorillas is (probably) nutritionally unnecessary since the prevailing level of inadvertent insectivory provides adequate nutrition.

Insect consumption by lowland gorillas

The situation is somewhat different for lowland gorillas. Lowland gorillas are known to more heavily consume social insects. Tutin and Fernandez [1992] analyzed the insect consumption of lowland gorillas and chimpanzees in the Lope Reserve, Gabon. They found insect remains in 27.4% of gorilla feces, versus 20.2% in chimp feces. Tutin and Fernandez disagree with the suggestion by Harcourt and Harcourt [1984] that deliberate insectivory by gorillas may be nutritionally unnecessary.

Tutin and Fernandez [1992] explain that lowland gorillas eat more fruit than mountain gorillas, and pre-process much of their herbaceous foods (using their hands). The result is that despite higher insect density in the lowland gorilla habitat, inadvertent insect consumption by lowland gorillas is less than that for mountain gorillas. They then conclude that deliberate insectivory is necessary for lowland gorillas. From Tutin and Fernandez [1992 (p. 36)], with my explanatory comments in brackets [*]:

However, given the relatively frugivorous diet and the selective processing of their herbaceous foods, inadvertent insectivory by gorillas at Lope is likely to be minimal and [deliberate consumption of] social insects probably serve the same critical role in nutrition as they do for chimpanzees. [Hladik & Viroben, 1974; Redford, 1987].

Actual mountain gorilla diets vs. fruitarianism

The choice of mountain gorilla as the "model ape" by advocates of fruitarian diets is both ironic and humorous. The mountain gorilla is a folivore and consumes little fruit. Schaller [1963] observed the mountain gorillas feeding, and he actually tasted some of the foods consumed by the gorillas. Schaller [1963] provides a table (table #39, p. 372) listing the plant species and parts consumed, and how they tasted. Of 24 plant species/parts listed, only 6 were fully palatable, 1 was described as "mealy," and the remaining 17 (~71%) were described as one or more of: bitter, sour, astringent, or resinous. Additional evidence that the gorilla diet is not very palatable to humans is in Koshimizu et al. [1994], which reports that ~30% of mountain gorilla diet items are bitter in taste to humans. Koshimizu et al. [1994] also cite an interesting hypothesis by Harborne [1977] that the mountain gorilla tolerates or even likes bitter-tasting foods.

The irony here is, of course, that the fruitarian advocates who use the mountain gorilla as "model ape" do not recommend a diet whose predominant tastes are bitter, sour, astringent, or resinous. Instead they often promote a diet that by default is high in sugar from modern, hybridized sweet fruits.

Bonobos: Last Stand for Extremists?

Now that the information that (regular) chimp diet includes some meat and insects is becoming well-known, some fruitarian extremists have adopted the diversionary strategy of disregarding chimps and trying to center attention on bonobos, the pygmy chimpanzee. The bonobo has not been studied as thoroughly as chimps. An additional attraction to the fruitarian extremist is the common figure of an 80%-fruit diet for bonobos. However, Chivers [1998, p. 326] reports that the figure of 80% fruit may be an overestimate:

The mean fruit-eating score for the pygmy chimpanzee (Pan paniscus) may be inflated by being presented as a proportion of fruiting trees, rather than relative to feeding time (which may be closer to 50% than to 80%; see Susman, 1984).

Note that the primary scientific research regarding bonobos is centered on their unique social organization, rather than their diet. More importantly, however, while ape diets are of value as a reference point in attempting to determine the diets of early (pre-human) hominids, diet varies considerably enough among primates that attempting to make definitive extrapolations from one species to another is unreliable. This is particularly the case with humans who, as we will see later, have a digestive system that is nearly unique among primates.

Other Implications of Ape Diets

Given that Fit Food for Humanity argues for vegetarianism on the basis that humans are very similar to the great apes, the new information that the great ape diets include at least some animal foods presents the advocates of comparative "proofs" with a problem. If the comparative method really "proves" that our diet should be that of the great apes, then the information that ape diets include some animal foods also "proves" that the human diet should include some animal foods as well. More precisely, it "proves" that we are not natural vegetarians, at least in the usual human sense. This point will be discussed further in a later section, where we will have some fun with the logic.

To Summarize:


(The Fossil-Record Evidence about Human Diet)

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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