diet "rule" indicates a strict fruitarian diet for humans.
Richard [1995, p. 186] provides further insight into the alleged "rule":
Within broad limits, then, body weight predicts the general nature of a primate's diet. Still, there are exceptions to the rule, and body weight is not always a good predictor even of general trends...
[W]hen finer comparisons are made among the species the rule loses its value altogether. Specifically, similarly sized species often have quite different diets.
Specific human features imply dramatic breakthrough in diet. Milton [1987, p. 106] also comments on the "rule":
In contrast [to australopithecines], members of the genus Homo show thinner molar enamel, a dramatic reduction in cheek tooth size, and considerable cranial expansion (Grine 1981; McHenry 1982; S. Ambrose, pers. comm.). In combination, these dental and cranial features, as well as an increase in body size, apparently with no loss of mobility or sociality, strongly imply that early members of the genus Homo made a dramatic breakthrough with respect to diet--a breakthrough that enabled them to circumvent the nutritional constraints imposed on body size increases in the apes.
The above quotes from Richard [1995] and Milton [1987] reflect that the body size "rule" is not strict, and that humans are a specific example of a species that has overcome it.
Additionally, recall that our preceding section on brain evolution discussed how human energy metabolism is dramatically different from all other primates. We humans expend considerably more energy on our brains--energy that is apparently made available by our reduced gut size, which itself is made possible via a higher-quality diet. By changing the internal energy budget to supply our large brains with energy, humans have also overcome the "rule" on primate body size.
| Analysis of Head, Oral Features, and Hands |
Introduction: the main claims
Oversimplistic either/or views of carnivorous adaptations. The various comparative "proofs" of vegetarianism often rely heavily on comparisons with true carnivores, e.g., lions, tigers, etc. The basic arguments made are that meat cannot be a "natural" food for humans, because humans don't have the same physical features characteristic of the small group of animals that are considered to be "true" carnivores. However, such arguments are based on an oversimplified and flawed view of adaptation; that is, the underlying assumption being that there is only one--or at least one main set of--physical adaptation(s) consistent with eating meat. Such arguments also ignore the high intelligence and adaptive behavior of humans.
Let's examine some of the claims made in Mills' The Comparative Anatomy of Eating, plus a few additional claims made in a recent extremist fruitarian book. (Out of politeness and to avoid what some might construe as inflammatory, the latter book will not be identified other than to say that it is a massive plagiarism of the book Raw Eating, by Arshavir Ter Hovannessian--a book published in English in Iran in the 1960s.)
Flawed comparisons that pit humans against "true" carnivores. The claims are made that the human body lacks the features of certain carnivores, hence we should not eat meat, as it is not "natural." The differences are as follows; carnivores have, but humans do not have:
- Sharp, pointed teeth and claws for tearing into the flesh of the prey.
- A jaw that moves mostly up and down, with little lateral (side-to-side) movement; i.e., the jaw has a shearing motion.
- A head shape that allows the carnivore to dig into prey animals.
- Additionally, carnivores are different from humans (and herbivores) in that carnivores usually swallow their food whole (humans chew their food). Also, carnivores generally do not have starch-digesting enzymes in their saliva, whereas humans do. Note: Claims regarding the morphology of the gut (digestive system) are discussed in the next section.
In The Comparative Anatomy of Eating, Mills summarizes the above analysis with the statement that:
An animal which captures, kills and eats prey must have the physical equipment which makes predation practical and efficient.
We shall see that this claim by Mills is incorrect if one interprets it only in morphological terms. Without further delay, let's now examine the above claims.
Logical problems of the comparative proofs
The above physical comparisons are accurate--clearly, humans do not have the jaws, teeth, or claws of a lion. However, to use this information to conclude that humans "cannot" eat meat, or "must have" the same physical traits as other predators to do so, or did not adapt to meat in the diet, is logically invalid and bogus. A short list of errors in reaching the above conclusion is as follows:
- Focusing on purely carnivorous adaptations rather than omnivorous ones. One clarification should be made immediately: This paper does not suggest that humans are true carnivores adapted for a nearly pure-meat diet. Although it may be that humans might be able to do well on such a diet (e.g., the traditional diet of the Inuit), the focus of this paper is to investigate whether meat can be considered a natural part of the human diet--certainly the paleoanthropological evidence supports that view. Thus the focus here is not on the bogus issue "are humans pure carnivores?" but on "are humans faunivores/omnivores?"
- Invalid black-and-white views. The conclusion above (that meat "cannot" be a natural part of the human diet) is based on a simplistic (incomplete/invalid) view of adaptation. That is, the conclusion is based on the implicit assumption that the specific physical adaptations of the lion, tiger, etc., are the ONLY adaptations that can serve their intended function, i.e., meat-eating. Inasmuch as meat is a small but significant part of the diet of chimps, however--who also lack the carnivore adaptations (sharp teeth, claws, etc.)--we observe that the assumption is obviously false.
- Various oversimplistic assumptions. The analysis is simplistic and makes many of the mistakes listed in the preceding section--i.e., it assumes the form/function linkage is strict, fails to recognize that the same form can serve multiple functions, etc.
- Overlooked differences in adaptive behavior. The analysis ignores critical differences in feeding behavior, i.e., the ones relating to the hunting/feeding behavior of omnivorous primates (e.g., the chimp) in the wild, which is well-known to be different from that of lions and tigers. Also, adaptive behavior (enhanced via human intelligence and technology--tools) allows humans to easily overcome many of the physical limitations of our physical form and morphology.
- Impact of tool use and language on morphology disregarded. The analysis ignores the impact that human intelligence has had on morphology, specifically the evolutionary effect of technology (stone tools and cooking), as well as possible morphological changes to support language--yet another unique human feature.
- Obvious explanations rationalized away as "illegitimate." A simple, summary answer to the question of how humans can hunt animals and eat meat without the physical adaptations of the lion and tiger is the obvious one implicitly ignored and rationalized by the advocates of simplistic comparative "proofs": We don't need sharp teeth, powerful jaws, or claws to capture and butcher animals because we have used (since our inception as a genus ~2.5 million years ago) tools (or technology--stone weapons) for that purpose. Over the eons, evolution itself has adapted our physiologies to the results of this behavior along unique lines, quite regardless of the hue and cry over the "illegitimacy" with which these behaviors/skills are regarded by those extremists promoting the bizarre idea that human dietary behavior should be strictly limited to what we could do "naked, without tools."
Technology, driven by our intelligence, supports adaptive behavior that allows us to easily overcome the physical limitations that the comparative "proofs" regard (incorrectly) as being limiting factors. Along similar lines, we don't need the strong bodies of a lion or tiger because we have something much more powerful: high intelligence, which allowed humans to become the most efficient hunters, and the dominant mammalian species, on the planet.
Examining comparative claims about the head, oral features, and hands
Now let's examine, in the subsections that follow, some of the claims of the comparative proofs (regarding the head, hands, oral features, etc.) in light of knowledge of prehistoric diets and evolutionary adaptation.
- Cheek Pouches: An Example of Vague Claims
Before considering more serious subjects, one vague claim occasionally made in comparative "proofs" is that humans and herbivores both have cheek pouches, or cheeks whose structure is somehow similar to cheek pouches, whereas carnivores do not. Frankly, the claim that human cheek structure is similar to cheek pouches is vague and hard to evaluate.
Note, however, one point is clear in this matter: humans do not have true cheek pouches as certain monkeys do. Richard [1995, pp. 195-196] notes that:
A cheek pouch is an oblong sac that protrudes when full from the lower part of the cheek. Food is moved between it and the mouth through a slitlike opening.
Richard [1995] also reports that cheek pouches may increase foraging efficiency and may assist in the pre-digestion of starchy foods. However, until those making claims regarding cheek pouches clarify their claims, the importance (if any) of this point, cannot be evaluated. Further, the function of the mouth and oral systems (including cheeks) is not restricted to eating--a point that is covered later, and one with particular relevance for humans given our special adaptations for language.
The cheek-pouch claim is included here as an example of how vague some claims made in comparative proofs can be. Extremely vague claims are hard to test and evaluate. Also, one cannot help but get the impression--based on the very vagueness of this claim--that its advocates are simply "reaching" to find any possible explanation, without regard for plausibility, efficiency, supporting evidence, etc.: a feature typical of extremism in general.
- Hands vs. Claws
The claim that meat cannot be a natural food for humans because we lack claws ignores the following:
- Simple tool-based technology part of human evolutionary adaptation. As described above, human intelligence supports the creation and use of technology--stone tools in the case of our early human ancestors. Technology--even stone tools--serves the same function as claws, and humans have used such technology since the very inception of the genus. A human equipped with stone tools is a very efficient hunter, and has no need of claws.
- Powerful synergism of versatile human behavior patterns. The human hunting pattern can be seen as an extension of the non-human primate predation pattern. Butynski [1982, p. 427] notes:
It seems that complex vocal communication, bipedalism and weapon-use are not essential for primates hunting small vertebrates, including mammals. Nevertheless, when the basic predation pattern of non-human primates is supplemented with these unique capabilities, the complete hominid hunting pattern emerges and with it the ability to efficiently hunt and utilize large mammals (Table 2). Evidence for meat-eating by non-human primates and contemporary human hunter-gatherers indicates that, during the evolution of these three components of the hominid hunting pattern, a 30 to 35-fold increase in the consumption of meat occurred--an increase perhaps already evident more than 2.5 million years ago (Fagan, 1974; King, 1976).
Clearly, thanks to technology (even as basic a technology as simple stone tools), humans do not need claws to be effective predators. Instead of claws, we have hands, similar to, yet different from, the hands of the great apes. Humans have fully opposable thumbs, but lack the ape/orangutan adaptations for tree-climbing; the primary adaptations are curved phalanges, curved metacarpals, and increased length of fourth digit; see Aiello and Dean [1990, pp. 379-385] for further information on this; also see Hunt [1994] for information regarding the special muscular adaptations of chimps for tree-climbing.
- Special tree-climbing adaptations lacking in humans. Note that the fact humans lack the important orangutan hand adaptations for tree-climbing, and chimp muscular adaptations for tree-climbing, directly contradicts the claims of certain fruitarian extremists who allege that humans have evolved for a nearly 100% fruit diet (without the use of tools). Consider that (according to the extremists) we are allegedly adapted to eat a nearly 100% fruit diet, yet we lack the critical adaptations to efficiently climb trees and pick that nearly 100% fruit diet. Something is not right here--specifically, such flawed claims.
- Versatility of the human hand. The human hand is a very versatile system, and its function is not limited to merely picking fruit. The very same hand can caress a lover, feed a person, brandish a weapon, or perform some other function. The application depends on the individual who owns the hand. The fruitarian claim that human hands were designed or evolved primarily for fruit-picking is just silly nonsense.
- Stone tools compensate for lesser human physical capabilities via intelligence. On a similar note, the use of stone tools (made by the human hand, driven by intelligence) to slaughter animals killed for food renders invalid the comparative proof claim (above) that humans "should" have a head shape that allows humans to "dig into" prey animals. Humans dig into prey using stone tools (which, by the way, were razor-sharp) and their versatile hands. Similarly, the (previous) claim by Mills that humans "must have" the same physical features as true carnivores is invalid for the same reasons. In other words, the use of even rudimentary stone tools and a different feeding behavior by humans avoids the selection pressures that gave lions, tigers, and other carnivores those characteristic wedge-shaped heads, as well as the other features considered to be typical of carnivores.
- Jaw Joints and Jaw Motion
Oversimplifications in comparative "proofs." One of the claims made in the comparative proofs is that the motion of the jaw joint of a true carnivore is largely a shearing (up-and-down) action, with limited lateral (side-to-side) movement. This is something of an oversimplification.
Sicher [1944] reports that certain bears and pandas can and do masticate or chew plant foods. Sicher reports that the jaw joint of the carnivore actually provides a screwing motion, which has both shifting and shearing motions. In cats (and crocodiles) there is very little shifting motion, i.e., the joint motion is mostly shear. However, in pandas the shifting motion is aided by strong masseter muscles which allow mastication--side-to-side chewing--of plant foods. Similar remarks apply to certain bears. (Although bears are omnivorous and pandas nearly herbivorous, their jaw joint is typical of the order Carnivora.)
Considering detailed features in isolation is misleading. Thus we note that the characterization of jaw motion as "shear-only" in "carnivores" (members of the order Carnivora) is an oversimplification. This is an example of how considering detailed features in isolation from other features can yield misleading results. It also reminds us that some members of the carnivore order are--surprise--predominantly herbivorous. Finally, the remarks regarding hands vs. claws apply here as well: humans never needed super-powerful jaw muscles to tear up prey animals because we used stone tools to cut them up instead.
- Teeth
McArdle [1996, p. 174] reports that the best evidence humans are omnivores comes from the teeth:
Although evidence on the structure and function of human hands and jaws, behavior, and evolutionary history also either supports an omnivorous diet or fails to support strict vegetarianism, the best evidence comes from our teeth...
In archeological sites, broken human molars are most often confused with broken premolars and molars of pigs, a classic omnivore. On the other hand, some herbivores have well-developed incisors that are often mistaken for those of human teeth when found in archeological excavations.
In previous sections, we have discussed how teeth are a good, but not infallible, indicator of diet. McArdle's remarks should be seen in light of the limits on the tooth/diet connection.
- Salivary Glands and Saliva
McArdle [1996, p. 174] reports that our salivary glands "indicate that we could be omnivores." Tanner [1981] reports that humans and the great apes share a class of proteins known as Pb and PPb in the saliva. These proteins help protect tooth enamel from decay due to carbohydrates and/or coarse plant foods in the diet. The presence of these proteins may be an artifact of past evolution, as the diet of humans is significantly different from that of the great apes. It may also reflect the status of humans as, figuratively, "eat nearly anything" omnivores/faunivores.
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(Evolution of the Human Oral System and Its Relevance to Diet, cont.)
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SEE REFERENCE LIST
SEE TABLE OF CONTENTS FOR:
PART 1 PART 2 PART 3 PART 4 PART 5 PART 6 PART 7 PART 8 PART 9
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
