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(Comparative Anatomy and Physiology Brought Up to Date--continued, Part 4C)

Fruitarian Evolution:
Science Fact or Science Fiction?

Despite the material of this (and preceding) sections, some fruitarian extremists are likely to continue to promote the tired, discredited "party line," i.e., that humans evolved under a fruitarian diet, and that the natural diet of humans is exclusively fruit or a very-high-percentage fruit diet. (Such claims were assessed and found unsupportable earlier in this paper.) However, there are a few aspects of these claims that merit additional discussion.

Vague claims about an ancient frugivorous primate ancestor

First, those who make such claims may refer to some vague, ancient, frugivorous primate ancestor, implying that such an ancestor somehow proves humans are natural fruitarians. There are two major problems with this:

No fruitarian, or even vegan, hunter-gatherer societies have ever been found. Further, there is no evidence to indicate there ever existed, in the past, a fruitarian (or veg*n) hunter-gatherer society. Even in the tropical rainforest, hunter-gatherers eat meat. (The Ache of Paraguay in the Amazon rainforest, one of the best-studied of all hunter-gatherer tribes, are a prime example with an average of over 50% meat consumption throughout the year, ranging from 47-77% depending on the season [Hill, Hawkes, Hurtado, and Kaplan 1984].) There is no evidence of any fruitarian societies, and--more to the point--the extensive anecdotal evidence (virtually the only evidence available) on modern attempts at (strict) fruitarianism indicates that it may work for a short while but almost always fails in the long run. (Even the fruitarian extremist "experts" often fail to follow the diet strictly, in the long term.)

Crank science and logical fallacies used in support of claims of fruitarian evolution

Returning to the false claims that humans evolved as fruitarians, the primary additional "evidence" presented in support of such claims consists of additional claims such as:

Fruitarian denial of physiological evolution/adaptation

What are the claims? Given the extensive fossil record evidence of meat consumption and physical evolution since the first appearance of the human genus ~2.5 million years ago, those who wish to promote the theory that humans evolved on, and are adapted to, a diet of only fruit (with perhaps a small amount of other plant foods) must make the following three unusual claims:

Note that those who claim humans evolved to be strict veg*ns, whether fruitarian or not, also must make claims similar to the above to be able to somehow "explain away" the evidence of long-term meat consumption provided in the fossil record.

Analysis of the Fruitarian Claims

Let's now examine, in depth, some of the "evidence" and additional claims raised by promoters of the fruitarian evolution theory.

CLAIM: Morphological evolution is "easy," physiological evolution is nearly impossible. The basic claim is that mutations that impact morphology--skin color, bone size, etc., have a minor impact on the organism, while mutations that produce physiological changes occur under what seem to be more complicated interactions, hence are less likely to succeed or enhance survival.

REPLY: The claim is not only misleading and an implicit oversimplification, but a good example of the way such claims are often hastily grasped at without thinking carefully through them first. As changes within the human body occur in a system in which both morphology and physiology are unified, physical changes often cannot be easily divided into two distinct categories, morphological and physiological. In reality, morphology and physiology are closely interrelated. Such morphological parameters as body size and shape are in fact regulated by hormones, which are part of your physiology.

Hormone regulation of morphology/physiology. For example, bone growth and size of the bones/body are regulated by pituitary growth hormones and sex hormones. In turn, the growth hormones are themselves regulated by releasing hormones produced by the hypothalamus, which is in the brain. (See Tortora and Anagostakos [1981], and Tanner [1992] for relevant discussion of hormones.) This implies that any significant evolutionary change in morphology requires an associated simultaneous change in physiology, i.e., the relevant hormones must change as well.

Thus we observe that a binary or "black-and-white" classification of changes as either morphological or physiological does not match well with reality. Once again, fruitarian extremists are engaging in the binary thinking and oversimplification that is characteristic of such dietary dogma.

As a postscript to this topic, the remark of Tanner [1992b] is relevant:

Differential growth rates are very often the mechanism of morphological evolution in primates...

The above suggests that morphological changes are driven by changes in growth rates, which are determined by hormones (physiology). This is quite interesting, for it indicates that morphological evolution is driven by physiological evolution.

CLAIM: The digestive system is extremely complex. For it to evolve in a mere 2.5 million years is simply not possible.

REPLY: The above is an unsupported rationalization. Consider that the human brain is far more complex than the digestive system, and that the physiology of the entire body is regulated via the autonomic nervous system, which is controlled by the brain. More precisely, some of the control of the autonomic nervous system rests in the cortex [Tortora and Anagostakos 1981, p. 374], and the cortex is the part of the human brain that is larger and has further evolved vis-a-vis the great apes [Stephan 1972]. Thus we observe that the "master controller" of the human physiology is the brain, with the cortex playing a key role.

Then we note that the human brain has in fact evolved (quite considerably) during the period, i.e., the "master controller" of the human physiology has evolved significantly in the last ~2.5 million years since the human genus first appeared. Thus, the bizarre claim that the physiology of the human digestive system could not have evolved during the period is easily seen as the ludicrous fantasy that it is.

CLAIM: Expert opinion is that physiological evolution is highly unlikely. From Jones [1992, p. 286]:

Mutations that deviate from the norm often interfere with biochemical processes and are rigorously removed by selection. Much of the body is made up of the building blocks of cells, which must fit accurately with one another... Any mutation that changes the shape of such molecules will almost always be at a disadvantage as it reduces their ability to interact with each other or with their substrate. Stabilising selection of this kind can be a very conservative force.

Stabilising selection is a powerful agent that leads to genetic homogeneity. To explain how genetic variation is maintained in the face of such widespread censorship by natural selection is one of the main problems of population genetics.

REPLY: The last sentence in the expert opinion quoted indicates, of course, that physiological evolution happens anyway. How this happens is precisely one of the interesting challenges spurring current research. The above quote has been used to support the claim that physiological evolution cannot have occurred. Yet genetic variation--and hence physiological evolution--happens anyway. The quote here has simply been twisted and misrepresented.

CLAIM: There is no convincing teleonomy proof that humans have adapted to a diet that includes meat!

REPLY: There is also no convincing teleonomy proof that humans have adapted to a strict fruitarian diet! The appeal to teleonomy is, thus, a red herring (i.e., a diversion) and nothing more.

Teleonomy, the scientific study of adaptations, is sometimes used as a defense of fruitarian evolution. Basically, the teleonomy proof argument is nothing more than a diversion--the fruitarian extremist demands what is implied to be definitive "proof," a teleonomy study or analysis, that "proves" humans have adapted to meat in the diet. Such claims are simply diversions, however, because those who make them do not have teleonomy "proof" that humans are adapted to a fruitarian diet either. In effect, the claim is used (if unconsciously) as a smokescreen to divert attention from the total lack of legitimate scientific evidence to support the fruitarian evolution theories.

A few comments on teleonomy are appropriate here. Thornhill [1996, p. 107] provides an introduction to teleonomy, and he defines teleonomy as:

...[T]he study of the purposeful or functional design of living systems and the directional pressures that have designed adaptations during long-term evolution.

Focus on evolutionary design and function. Teleonomy is primarily interested in phenotypic design and adaptation as they relate to the selective pressures that drive evolution. The focus is on the evolutionary function of adaptations, rather than the evolutionary origins of adaptations (see Thornhill [1996, p. 108]). The role of genetics in teleonomy studies is unclear from the discussion in Thornhill [1996], as Thornhill appears to regard such information as being of very limited value (pp. 116, 122-124). A relevant point here is that the fruitarian extremists who use the teleonomy argument may also simultaneously demand "proof" in the form of genetic models (which Thornhill, the teleonomist, suggests are of limited value in teleonomy). It seems odd to demand genetic "proof" in the context of a system where it is used only occasionally.

Criticisms and limitations of teleonomy. Teleonomy is also known as the adaptationist program, and a well-known critique of the subject is provided by Gould and Lewontin [1994]. An interesting paper on the many statistical challenges faced in doing teleonomy studies is Pagel and Harvey [1988]. As will be discussed later in this paper, humans are unique in nature by virtue of certain important features: high intelligence, language, etc. This uniqueness, coupled with the serious statistical problems inherent in cross-species comparisons, presents major statistical and analytical challenges to those who wish to unequivocally "prove" adaptation in humans (vis-a-vis other species) via teleonomy studies. As such, perhaps the best way to view teleonomy is as one analytical tool (out of many tools) available to the researcher, rather than the "best tool" or "only (valid) tool," which is what fruitarian extremists appear to imply in their use of teleonomy as a last-ditch defense of their crank science theories.

CLAIM: There are no examples of animals evolving backwards from a vegetarian to an omnivorous diet!

REPLY: Evolution does not move backwards or forwards. Evolution occurs as the result of changes over time, the result of selective pressures in the environment (which can include behavior, especially for humans, per discussion in a previous section). The use of the word "backwards" shows the emotional nature of the fruitarian evolution claims. The idea that evolving from a vegetarian diet to an omnivorous (or faunivorous) diet is "backwards" is purely a subjective bias. Nature simply IS; our subjective opinions of the process are irrelevant.

CLAIM: If humans are adapted to eating meat, what exactly are those adaptations?

REPLY: The answer to this question will be apparent in the later sections of this paper. Though a short answer could be given here, it would remove the element of surprise from some of the following sections. This question is answered and addressed later with relevant details and context.

In summary, those who cling to crank science/science-fiction theories that humans evolved as fruitarians must also cling to incorrect logic and fantasies which state:


(Further Evidence Against the Claims of Fruitarian Evolution)

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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