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(Comparative Anatomy and Physiology Brought Up to Date--continued, Part 8G)

Examining Fruitarian Claims
about Instinct in Food Selection

Introduction. This section catalogs and addresses a long set of claims about instinct made by a few fruitarian extremists. The claims are summarized and paraphrased here, to respect copyrights. The material below includes supplementary information on primates (hunting habits, fauna consumption, and use of medicinal herbs); the hunting skills of prehistoric humans; child/infant food preferences; and other topics of potential interest to rawists and/or veg*ns. If you are short on time, you might skim the material below, reading only the items of interest, or if you prefer, skip to the next section.

CLAIM: Humans are limited to a narrow diet (nearly 100% fruit) by our genetic code. Instinct is a function of genetic code.

REPLY: Extensive real-world evidence indicates humans thrive on a broad spectrum of diets. Morphology and physiology are functions of DNA, and the existence of structural limits is implied. However, the obvious (and overwhelming) evidence of individuals thriving on a wide variety of diets--ranging all the way from hunter-gatherer to conventional veg*n--indicates that humans can succeed on a wide array of diets. (We are not limited to ~100% fruit diets, and fruitarian diets have a dismal record of failure in the long-term.) One must wonder whether humans are really limited to "narrow" diets, or is it the case that the extremist making the claim simply limits themselves emotionally to their own narrow view?

One further point here: Intelligence plays a role in morphology and physiology, both via brain evolution and via the culture/evolution feedback loop discussed in an earlier section.

CLAIM: The "instinct" to hunt and kill animals is not found in every human, hence it cannot be an instinct. Example: Most all domestic cats still have an instinct to hunt.

REPLY: The above has already been addressed to a certain extent (instinct vs. intelligence discussion), so we'll only make a few additional points here.

CLAIM: Children instinctively choose sweet foods, like fruit. Parents bribe their children to get them to eat (repulsive!) animal foods.


  1. Sweetness is a sign of carbohydrates--calories/energy--in food, and there is reason to believe that for increased evolutionary survival, the desire for sweet may be instinctive or evolutionary (but see points 4 and 5 below). But sweetness is not the only naturally attractive taste characteristic in foods that appeals to children (point 4 below).

  2. One should not discuss sugar without mentioning that fruit is of limited and/or sporadic availability in most environments, even the rainforest. The evidence of orangutans (Knott [1998], Mackinnon [1974, 1977] as cited in Chapman and Chapman [1990]) suggests that fruit is not always available, even in remote, pristine rainforest habitats.

  3. Sugar consumption may impact opioid receptors in the brain; see Blass ([1987], a heavily-referenced review article) for a discussion of this topic. Market acceptance is an important factor in the breeding programs for modern fruits, and sweetness (high sugar content) is an important factor in such breeding programs.

  4. Research on infant food preferences contradicts some fruitarian claims. Story et al. [1987] review the research of Clara Davis done in the 1920s and 1930s. Davis gave infants a free choice of a wide array of foods on a tray. Story et al. [1987] reports the favorite foods chosen by the infants (p. 104):

    Bone marrow was the largest single source of calories (27%) for one infant, whereas milk provided the bulk of calories for the other two (19% and 39%). All three infants shared a low preference for all 10 vegetables, as well as for pineapple, peaches, liver, kidney, ocean fish, and sea salt. These foods constituted less than 10% of the total energy intake. Davis observed that the infants ate much more fruit, meat, eggs, and fat than pediatricians typically advised.

    The results of Davis obviously confirm some preference for sweet foods. However, the results of Davis also indicate additional taste preferences, and discredit the claim that children are repulsed by animal foods; after all, bone marrow was the favorite food for one infant and prized by the other two infants as well. (Once again, it can be seen that the real limitations here exist in the highly emotional, narrow thinking processes of the extremist rather than in nature.)

    It should be clearly noted that the results of Davis are based on small samples. Despite this, they are intriguing, as they contradict most so-called "wisdom" about children's food preferences.

  5. First reaction to sugar can be negative. If the response to sugar is truly instinctive, and instinct is universal per a previous claim, then one would expect those who live without sugar to react in a very positive way when they finally get to (first) taste it. The quote below from Stefansson [1960 (p. 86)] suggests that this is not necessarily the case (italicized emphasis mine, in the following).

    The Copper Eskimos, so named because many of their weapons and tools were of native copper, had never dealt with any traders before 1910. They did not even know tea, used no salt, and lived exclusively on flesh foods, eating roots and such only in time of famine. In 1910, they for the first time tasted sugar, given them by the first trader to reach Coronation Gulf, Joseph Bernard. They disliked it.

CLAIM: Eating meat is a learned behavior, and not instinctive. Humans have been eating meat for "only" 2 million years.

REPLY: This has already been discussed extensively earlier in this paper.

CLAIM: Some humans are disgusted at the thought of eating meat. How could that happen to a true carnivore?

REPLY: (Sarcasm) Some humans are disgusted at the thought of eating durian (a smelly tropical fruit revered by some, hated by others). How could that happen to a true frugivore?

More seriously, the suggestion that we are true carnivores is a straw argument. Instead, the evidence presented here supports the claim that humans are natural omnivores/faunivores, not total carnivores. (Although it may be possible humans might be able to survive--and survive well--as carnivores, e.g., the Inuit.)

As for the disgust factor, given the role of animal foods in evolution and hunter-gatherer societies, is not such disgust merely the result of one's own: (a) moral/religious views, or (b) self-conditioning with veg*n dogma?

CLAIM: True carnivores often eat (only) their prey's internal organs and leave the muscle for the vultures. Why don't human meat-eaters behave this way?

REPLY: Animal organs are widely consumed in many cultures, and by hunter-gatherer groups (see O'Dea [1991] for a discussion of this regarding the Aborigines of Australia). Humans are different from lions in a number of ways, as follows.

The next set of claims deals with form, function, and primates.

CLAIM: Primates have adaptations exclusively for fruit eating--vision, hands, etc. True carnivores usually do not have adaptations for fruit-eating.

REPLY: Here, another form of straw argument comparing humans to true carnivores is erroneously brought up. However, on the subject of fruit-eating adaptations, as discussed in an earlier section, chimps and orangs have special adaptations for tree-climbing, which are very handy for a frugivore. Humans lack these important (frugivore) adaptations for efficient fruit-collecting. The idea that our vision and hands are exclusively for fruit-eating is utterly ridiculous--such claims were examined (and found lacking) in earlier sections herein (e.g., a single form can support multiple functions; adaptation is not limited to one specific form; etc.).

CLAIM: True carnivores hunt by smell alone; they don't need technology.

REPLY: Repeating the straw argument, "Humans are not like true carnivores," does not make it relevant. Chimps, and (omnivorous, not carnivorous) primates in general, hunt by sight and not by smell. (This point is discussed further later in this section.) Humans are a special kind of primate; we are not lions or tigers.

CLAIM: The great apes, except for chimps, are strict vegetarians.

REPLY: This claim is simply in error and is typically based on outdated research. Modern research from roughly 1970 onward has revealed that the apes other than chimps also eat a modicum of insects and/or other animal foods in their diet. See the earlier section on ape diets for details.

CLAIM: Hunting by chimps is not instinctive, because:

  1. Female chimps do not hunt.
  2. The males kill prey only by knocking it to the ground.
  3. Chimps have smaller bodies than humans, hence need concentrated foods to support higher metabolism.
  4. Chimps get sick from eating meat and must resort to "toxic" herbs.

REPLY: The above is a good example of the sort of misinformation and half-truths frequently dispensed by fruitarian extremists. Let's look at the above claims one at a time.

  1. In fact, female chimps do hunt, and males generally share their kills with females. The paper of Galdikas and Teleki [1981] provides the best answer to this claim (pp. 241, 245, 247):

    Long-term research at Gombe National Park indicates that chimpanzees, more than any other non-human primate in existence today, practice an incipient form of labor division; one age/sex class, adult males, focuses on exploiting certain [food] resources, especially vertebrates, to the benefit of other members of the social unit, including individuals of other age/sex classes (Teleki 1973a, Wrangham 1975)...

    The specialization is not absolute: chimpanzee females occasionally hunt game and males certainly spend considerable time collecting insects...

    Further since female chimpanzees benefit from male predatory activities through the extensive sharing of meat within a community, while males benefit little if at all from female collecting activities because insects are rarely shared among adults, it is possible that the annual intake of fauna is greater among chimpanzee females than among males (McGrew 1979)...

    Modern field studies are demonstrating that monkeys, apes and humans are, with some exceptions, basically omnivorous mammals that share many adaptive responses to resource availability (see Harding and Teleki 1980).

  2. Male chimps are not limited to knocking prey to the ground; they often use the method of flailing to kill their prey. See van Lawick Goodall [1973] and Butynski [1982] (table 2, p. 425) for a summary discussion of chimp hunting methods.

  3. The claim about body size was examined and found wanting in an earlier section herein. By the way, to claim that any primate smaller than humans needs more concentrated food would suggest that orangs, bonobos, and gibbons probably all need to eat meat also.

  4. Medicinal herb use by chimps. The claim that chimps get sick and use herbs has some truth in it. However, herb use does not constitute proof that meat-eating by chimps is somehow non-instinctive. The claim (#4) made above implicitly includes two myths promoted by raw fooders: First, the false myth that wild animals who eat their "natural" diet never get sick. This myth was assessed earlier, and a short discussion of the topic is given in the article, Selected Myths of Raw Foods. The second myth is that herbs (and spices and meat and anything else the fruitarian extremist dislikes) are "toxic."

    The field of self-medication (using herbs) by animals, known as zoopharmacognosy, is discussed in Huffman [1997], which provides an overview of the topic. Self-medication in primates is primarily used to control parasites and gastrointestinal disturbances. Huffman [1997] also discusses possible self-medication by bears. The obvious logical fallacy of the extremists is to assume (without any credible scientific proof) that such herb usage is unnatural.

    Inasmuch as some raw fruitarian extremists are quick to label almost everything (except fruit, and perhaps a few greens) as "toxic" and "bad," the following quote from Huffman [1997, pp. 171-172] confronts such extremist thinking with the reality that primates have the general ability to handle (detox) a wide range of plant compounds.

    Among primatologists a major focus of concern about plant secondary compounds in the diet has been on how and why primates can cope with their presence (Glander, 1975, 1982; Hladik, 1977a,b; Janzen, 1978; McKey, 1978; Milton, 1979; Oates et al., 1977, 1980; Wrangham and Waterman, 1981). An extreme case in point is the golden bamboo lemur (Hapalemur aurensis) of Madagascar, which is noted to consume over 12 times the lethal adult dose of cyanide in a day, without ill effect (Glander et al., 1989). The cyanide comes from the tips of a bamboo species, Cephalostachyum sp. (Graminaea), consumed as part of the lemur's daily diet at certain times of the year (Glander et al., 1989). In this case, the cyanide is thought to be detoxified mostly in the liver (Westly, 1980).

CLAIM: Meat-eating by humans cannot be instinctive because humans don't eat the specific monkeys that chimps hunt.

REPLY: The above claim reflects truly amazing ignorance of chimp (and human) hunting behavior. It suggests that the only meat that chimps eat comes from monkeys. This is both false and absurd. Hamilton and Busse [1978, p. 764] note:

Predation upon mammals by chimpanzees and baboons is usually opportunistic, i.e. prey animals are encountered at close range and are captured quickly with a high probability of success, a typical scavenge-hunting tactic.

Van-Lawick Goodall [1973] provides a list of prey killed by the chimps of Gombe; it includes many vertebrates that are not monkeys. Teleki [1981, table 9.3, p. 314] reports that of the identified mammalian prey killed by Gombe chimps, 68% were primates, and 32% were non-primates.

Having ascertained that the basic premise of the claim is false, let's look at reality. Many humans live in temperate climates where there are no monkeys. Why does the extremist suggest that humans should eat only monkey meat, and no other kind of meat? Especially when it is contradicted by the reality of wild chimp diets, and the fossil record of the prehistoric human diet?

CLAIM: Humans cannot eat meat because we lack fangs, claws, sharp teeth. Human teeth are good only for eating fruit, and not for tearing flesh or chewing leaves.

REPLY: The above claims were investigated thoroughly in earlier sections and found specious.

CLAIM: Humans are fully upright and bipedal, and this makes us ineffective at hunting.

REPLY: Such a claim might be hilarious if it were intended as humor. Unfortunately, the extremist here is serious. As for hunting, we are all the descendants of hunter-gatherers. There are no veg*n gatherers, and no evidence that any ever existed. If humans were really ineffective and/or incompetent at hunting, then one of the following would be true:

However, we are alive today to discuss the fine points of diet, which indicates that our hunter-gatherer predecessors were effective enough at hunting to pass the critical test of survival of the fittest.

Humans are the only primate to prey on vertebrates larger than self (body size). In reference to the above, Butynski [1981, p. 427] notes:

No primate other than man has been observed to prey upon animals larger than itself... In contrast, man frequently kills mammals many times his size.

Milton [1987] (citing Rodman and McHenry [1980]) reports that bipedalism is more energy-efficient over land than is quadrupedalism. Humans, of course, are the only fully upright bipedal primate.

Prehistoric humans hunted many species to extinction. The considerable skill of humans at hunting is summarized by Allman [1994, p. 207]:

Our modern human ancestors' hunting abilities are strikingly apparent in the Americas, where Paleoindians hunted to extinction nearly 70% of the species of large mammals on the continent, including mammoths, camels, and giant sloths...

The most important factor in our ancestors' hunting prowess, however, was not their new tools, but their psyche. Large, relatively clumsy, and slow of foot, our ancestors could not stalk their prey and swiftly chase them down, like many predators, but instead had to rely on working together as a team to bring down their prey--something at which modern humans excelled.

Note the reference in the above quote to the social and cultural behavior of prehistoric humans hunting in cooperative groups. This is an example of adaptive behavior that exerted selective pressure on human morphology and physiology via evolution. Recall the simplistic comparative "proof" arguments about human dental structure, body structure; such arguments are clearly fallacious because they implicitly assume that humans hunted solo, without technology (e.g., like cats). For additional information on human hunting skills and species extinctions, see Martin [1990].

CLAIM: Due to body size "rules," large mammals (like humans) don't have to eat flesh.

REPLY: The body size rule has been discussed already. The above claim would suggest that lions, tigers, killer whales, and polar bears don't need to eat flesh. Remember too that some very large land carnivores are now extinct: sabertooth tigers, prehistoric lions (about twice the size of modern day lions), etc. They didn't need to eat flesh either? Are such claims an example of denial of reality, or science fiction?

CLAIM: Cooking was needed because eating raw meat introduced parasites.

REPLY: One can contract certain parasites from any raw food, including raw plant foods. All that is needed is the presence of parasite eggs or bacteria, and these can be carried by water, insects, birds, are found in animal dung, and so on. If indeed cooking was universally required to neutralize parasites in meat, this implies that cooking would have been universally needed for plant foods as well. Of course, that contradicts the extremist view that humans evolved on a diet of raw fruit.

CLAIM: Humans are not adapted to be omnivores. The writings of D.J. Chivers are then quoted by the extremist, in a misleading way.

REPLY: This is discussed in an earlier section. In my opinion, to use quotes in a deliberately and grossly misleading way is intellectually dishonest. (If it is not deliberate, it shows how seriously the extremist's fanaticism filters their perception of what they read, and how it predisposes them to screen out or distort, perhaps subconsciously, what they do not want to hear.)


I hope the preceding set of claims and replies was interesting--at least in part--to you. The mixture of half-truths and twisted "logic" found in the above claims is typical of crank science. Unfortunately, a significant part of "fruitarian science" is composed of these types of distortions.


(Conclusions: The End, or the Beginning of a New Approach to Your 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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