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(Comparative Anatomy and Physiology Brought Up to Date--continued, Part 6E)

A footnote on Chivers and Hladik [1980, 1984]: Human gut morphology

Sussman [1987] describes the analysis of the gut of 6 human cadavers using the measures defined in Chivers and Hladik [1980, 1984]. Analysis of the human gut data using the coefficient of gut differentiation (a measure of gut specialization) placed humans in the frugivore range, along the margin with the faunivore category. However, analysis of the same data using the index of gut specialization (yet another measure of gut morphological specialization) placed humans squarely in the faunivore range.

Note that the frugivore classification above came from using the coefficient of gut differentiation, which is an intermediate result in Chivers and Hladik [1980, 1984], hence presumably less desirable (from a certain analytical viewpoint) than the (faunivore) classification achieved using the end result of Chivers and Hladik [1980, 1984], i.e., the index of gut specialization. Also recall that the term frugivore does not mean or imply that a diet of nearly 100% sweet fruit (as advocated by some fruitarians) is appropriate. Recall that all frugivorous primates eat at least some quantities of animal foods, even if only insects. Thus the result that humans appeared to be frugivores by one measure and faunivores by another suggests a natural diet for humans that includes both animal foods and fruits.

The research of Martin et al. [1985]

Improved methodology. The research of Martin et al. [1985] is very important, for it provides a second, different analysis of the (same) data analyzed previously in Chivers and Hladik [1980, 1984]. The analysis of Martin et al. [1985] includes a number of important features/improvements:

See Appendix 4 for background information on statistical methods used in the paper.

The major points from Martin et al. [1985], in summary, are:

The research of MacLarnon et al. [1986]

Refinement needed in analytical techniques used in earlier study. The research of MacLarnon et al. [1986] provides an extension and analytical refinement of Martin et al. [1985]. The analytical techniques needed further refinement because:

MacLarnon et al. [1986] addressed the above issues by performing additional analyses of the Martin et al. [1985] data set:

The results of MacLarnon et al. [1986] can be summarized as follows.

Conclusions. MacLarnon et al. [1986] conclude that:

Thus the research of MacLarnon et al. [1986] suggests, but is not (by itself) conclusive proof, that the human GI tract is adapted for the consumption of animal foods.

Assessing Martin et al. [1985], MacLarnon et al. [1986], and related studies

Further study still needed to confirm results. Although very impressive in their scope and sophistication, the results of Martin et al. [1985] and MacLarnon et al. [1986] that relate to humans specifically are based on limited data (6 individuals). Further study is appropriate before sugrfficient evidence is available to definitely class humans as faunivores or frugivores, based solely on gut morphology.

Some of the reasons for caution regarding the study results are as follows:

We have presented the results of these papers in some detail here, so the reader can get a feel for the overall thrust of the analyses. The basic result appears to be that the anatomy of the human GI tract shows what appear to be adaptations for faunivory (consumption of animal foods), regardless of whether humans fall into the faunivore or frugivore class. This leads us to the next paper on gut morphology to be discussed here.

The note of Hladik et al. [1999]

A recent note: Hladik, Chivers, and Pasquet [1999] (referred to hereafter as Hladik et al. [1999]) provides further information on gut morphology. The Hladik et al. [1999] paper must be understood in the context of the 4 major papers that preceded it, as well as the fact that it is a comment on the Expensive Tissue Hypothesis of Aiello and Wheeler [1995], which was discussed in a previous section. The context is important because a fruitarian extremist has already quoted parts of Hladik et al. [1999] out of context, and--in my opinion--misrepresented the meaning thereof.

Postscript: humans are where faunivore and frugivore "meet." The Hladik et al. [1999] note reminds us that gut morphology alone probably won't settle the issue of whether humans should be classed as frugivores or faunivores. Indeed, it might not be possible to unequivocally "prove" humans are in one class but not the other. One point is clear, though: gut morphology suggests that humans are where the classes of faunivores and frugivores "meet," i.e., it suggests that animal foods (even if just insects) are a part of the natural human diet.

On the term "omnivore," and misuse of quotes

Definition of "omnivore" a critical point

Out-of-context quotes from the writings of D.J. Chivers are sometimes used by fruitarian extremists in support of their claims that humans are not omnivores, but are instead adapted to a strict vegetarian/fruit-based diet. From the previous material in this section, recall that the research of Chivers and associates suggests that the human gut morphology is similar to that of faunivores, meat-eaters (which suggests that animal foods are part of the natural human diet), and does not support the alleged claim that humans are adapted for a nearly 100% fruit diet, or even a 100% vegetarian diet.

One major factor in understanding the quotes from Chivers regarding omnivores is that he uses the word in a more precise and different way than the most common usage. To understand this point, let's now examine the different definitions of the term "omnivore."

Omnivore: the common definition. The most common usage of the term omnivore is to indicate an animal that includes foods from more than one trophic level in its diet, which is usually interpreted to mean an animal that eats both plant and animal foods. From Milton [1987, p. 93]:

Humans are generally regarded as omnivores (Fischler 1981; Harding 1981). By definition, an omnivore is any animal that takes food from more than one trophic level. Most mammals are in fact omnivorous (Landry 1970; Morris and Rogers 1983a, 1983b)...

Milton [1987] goes on to note that the term omnivore is vague as there is substantial variability in the foods omnivores eat, and the term is not linked to gut morphology. Thus saying a mammal is an omnivore tells one little about the actual diet of the animal.

Omnivore: Chivers uses the term differently. Let's review some of the relevant quotes. From Chivers [1992, pp. 60-61]:

[F]or anatomical and physiological reasons, no mammal can exploit large amounts of both animal matter and leaves, the widely used term "omnivore" is singularly inappropriate, even for primates. Humans might reasonably be called omnivores, however, as a result of food processing and cookery...

Because of cooking and food processing, humans can be described as the only omnivores, but we shall see that their [human] gut dimensions are those of a faunivore.

"Omnivore" a vague term lacking in relevance for GI tract functions. A further relevant quote is from Chivers and Langer [1994, p. 4]; emphasis below is mine:

The concept of omnivory is weakened by the anatomical and physiological difficulties of digesting significant quantities of animal matter and fruit and leaves... animal matter is swamped in a large gut, and foliage cannot be digested in a small gut. A compromise is not really feasible... Humans are only omnivorous thanks to food processing and cookery; their guts have the dimensions of a (faunivore) carnivore but the taeniae, haustra and semi-lunar folds are characteristic of folivores. Among the so-called omnivores, most eat either mainly fruit and animal matter (if smaller) or fruit and foliage (if larger) but not all three.

Thus we note that Chivers appears to define an omnivore as a general feeder with a gut morphology that supports a diet that includes significant amounts of all three types of foods: fruits, leaves, and animal matter. Such a gut morphology is not found in mammals, hence the term is indeed inappropriate for mammals.

Contradictory claims about omnivores: which is correct? Thus we have what appear to be contradictory statements: most mammals are omnivores; no mammal is an omnivore. Which is correct? The answer is that both are correct, because they are using different definitions of the term "omnivore."

Chivers' criticism of the common definition of the term "omnivore" is relevant: it would be better (more precise) to use terms that are linked to gut morphology: folivore, frugivore, faunivore. However, that does not mean that those who are using the common definition are making incorrect or invalid statements. Recall that a definition is simply a convention that people follow. While it is desirable that definitions possess analytical rigor, it is not a requirement that they do so. Hence the meaning of a statment like "chimps are omnivores" or "humans are omnivores" is clear, i.e., the natural diet of humans and chimps includes both animal and plant foods.

A fruitarian extremist has used the difference in definitions of the term "omnivore" to suggest that statements like "chimps are omnivores" are incorrect and irrelevant. Because the meaning of such statements is clear (even to those who support Chivers' remarks), it is my opinion that the fruitarian extremist is engaging here in a blatantly intellectually dishonest word game in an effort to distract attention from the well-known fact that animal foods are a significant (even if small) part of the natural diet of many primates.

More examples of out-of-context quoting by dietary extremists. Those who use (some or all of) the above quotes from Chivers' writings in support of the fallacious claim that humans evolved on a strict vegetarian/fruit diet often neglect to quote the following, from one of the same source articles, e.g., Chivers [1992, pp. 60, 64]:

Exclusive frugivory is practically impossible, because certain essential amino acids and other nutrients are found only in leaves or in animal matter...

Humans are on the inner edge of the faunivore [meat-eater] cluster, showing the distinctive adaptations of their guts for meat-eating, or for other rapidly digested foods, in contrast to the frugivorous apes (and monkeys).

The first part of the above quote indicates how unlikely the bogus claims that humans evolved as fruitarians (on very low-protein diets) really are. The second part of the above quote points out that human gut morphology is more similar to that of faunivores than the fruit-diet frugivores.

Finally, readers should be aware that a more recent paper, Chivers [1998], includes quotes similar to the above. This is mentioned in the event the fruitarian extremist in question here might decide to "update" their argument by utilizing more recent quotes from Chivers than the ones above.

Misuse of other quotes

Speaking of intellectual dishonesty and misuse of quotes, another quote on gut morphology that is sometimes misused by fruitarian extremists is from Elliot and Barclay-Smith [1904], as cited in Stevens and Hume [1995, p. 112]:

There can be little doubt that the human colon is rather of the herbivorous than carnivorous type.

By itself, the above quote may seem straightforward enough. However, now compare the above to a more complete version of the same quotation in full context, from Stevens and Hume [1995, p. 112] (italicized emphasis mine below):

They cited a study of 1,000 Egyptian mummies that indicated that their cecum was considerably larger than that of present-day humans. Therefore, in spite of reservations about deducing function from structure, these investigators concluded that, "There can be little doubt that the human colon is rather of the herbivorous than carnivorous type."

As previously mentioned, human gut dimensions can vary with diet. The diet of ancient Egyptians would likely be much higher in fiber than a modern Western diet of processed foods. See Milton [1987] for more information on this topic.

The above questionable use of a quote is yet another example (in my opinion) of intellectual dishonesty by a fruitarian extremist. The moral of the story here is that checking the references can be critical, particularly where only a few references have been (perhaps selectively) quoted.

Section summary and synopsis

Although by comparative anatomy analysis (alone) the issue is not yet settled, the results of two different statistical analyses of a "large" data set on gut morphology and diet (i.e., the best available scientific evidence) support the idea that animal foods are a natural part of the human diet. That is:


(Vitamin B12: Rhetoric, Reality, and Vegan Diets)

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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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