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

Further Evidence Against the Claims
of Fruitarian Evolution

Fully upright bipedal posture, lack of arboreal adaptations

Unfortunately for the proponents of fruitarian evolution theories, there is evidence that we did not evolve as pure fruitarians, over and above the extensive fossil record evidence of human consumption of animal foods (fauna).

Quadrupedal vs. bipedal adaptations and tree-climbing. First, humans are fully upright and bipedal, while apes are quadrupedal (though chimps, bonobos, and gorillas, of course, do have limited bipedal abilities). A fully upright bipedal posture is a major disadvantage in tree-climbing compared to quadrupedal motion--it is easier and safer to navigate trees when one can grasp and hold with four extremities rather than two, as humans must. That is, a fully upright bipedal posture is a disadvantage, overall, in collecting fruit--and hence would reduce survival of the alleged "pure fruitarian" prehistoric humans or proto-humans.

Bipedalism/quadrupedalism and fruit-picking. The hypothesis has been advanced that bipedalism evolved because it is more efficient to pick small, low-growing fruits [Hunt 1994]. Standing up to pick low-growing fruits allows use of both hands to pick fruit, and may allow more efficient harvesting of small fruit from small trees. However, this hypothesis [Hunt 1994] that bipedalism evolved as a fruit-picking strategy, specifically refers to chimps and australopithecines. Even then, it is well-known that chimp diet is not exclusively fruit; their diet also includes small but nutritionally significant amounts of fauna (insects, meat), along with other foods such as leaves and pith. Also, chimps retain quadrupedal motion and arboreal capabilities which they use for efficient fruit collection in larger trees. Hunt [1994] also discusses special muscular adaptations in chimps for vertical climbing (trees) and hanging (from trees).

As for Australopithecus, radio-isotope studies indicate that Australopithecus was an omnivore/faunivore, and not a fruitarian. (See Sillen [1992], Lee-Thorp et al. [1994]; also Sillen et al. [1995].) Thus even if bipedalism did evolve initially as a specialized fruit-picking mechanism, the evolution occurred within the framework of an omnivorous/faunivorous diet (or a frugivorous diet that specifically included nutritionally significant amounts of fauna), not a strict fruitarian diet.

Actual fruit availability/dependability fluctuates with location and time. Note that the hypothesis of Hunt [1994] does not suggest or imply that chimps or Australopithecus had a fruit-only diet. Also note that even in a savanna environment, fruit is not limited to low-growing trees. Consider the major restrictions placed on the survival of our prehistoric ancestors (or even modern-day chimps) if their diet were limited to only fruit picked within 2-3 meters of the ground. Such a restriction would greatly reduce survival, not increase it.

A pure fruitarian needs a year-round supply of large amounts of fruit, and the ability to efficiently harvest as much of the available fruit as possible. That is, one needs to be able to efficiently pick most of an entire, tall tree--hence needs effective tree-climbing ability, that is, quadrupedal motion and arboreal adaptations.

Different adaptations, different tradeoffs. In contrast, an omnivore/faunivore for whom fruit is only a part of the diet, and who effectively hunts/harvests other high-calorie foods (e.g., animal foods) can easily afford the loss of overall efficiency in fruit harvesting that fully upright bipedalism (as in humans) involves. This is particularly true if bipedalism enhances the ability to harvest high-calorie foods (fauna) by increasing hunting efficiency. (Hunting efficiency is discussed in a later section.)

The set of adaptations of chimps--limited bipedal ability that improves efficiency in picking fruit from small trees, combined with quadrupedal/arboreal adaptations to efficiently harvest fruit from tall trees, appears to be the optimal adaptation set for a primarily frugivorous animal. However, humans clearly do not have all of these important survival adaptations. In regard to humans, Hunt [1994] argues that (p. 198):

Accordingly, scavenging, hunting, provisioning and carrying arguments for the origin of bipedalism (Shipmam, 1986; Sinclair et al., 1986; Carrier, 1984; Wheeler, 1984; Lovejoy, 1981; Jungers, 1991) are more convincing explanations for the refinement of locomotor bipedalism in Homo erectus, as are heat stress models (Wheeler, 1993).

Adaptations must be interpreted in context. That is, even if the hypothesis of Hunt [1994] is correct, the later improvements in bipedal motion associated with Homo erectus (which evolved approximately 1.7 million years ago) are likely associated with the role of early humans as hunters, and not as fruit-gatherers. Inasmuch as humans are a separate genus from chimps and Australopithecus, the later developments are, of course, more relevant.

Aiello [1992, p. 43] points out that:

In fact, at walking speeds human bipedalism is significantly more efficient than ape quadrupedalism.

Needless to say, a fruitarian ape needs quadrupedal abilities for harvesting fruit from tall trees, and the lack thereof (in humans) suggests that harvesting fruit was much less important than the fruitarian evolution advocates claim. Additionally, note that humans did not evolve the special (orangutan) hand adaptations for tree-climbing (this is discussed further in a later section, with accompanying citations), and we also lack the special muscular adaptations of chimps [Hunt 1994] for arboreal motion. In contrast, fully upright bipedalism made walking--and hunting--far more efficient, at the cost of reduced efficiency (overall) in fruit harvesting.

Body size and tree-climbing. Finally, the body size of humans may be very questionable for a pure fruitarian. Humans are larger than orangutans, the most arboreal of the great apes, and we are larger than chimps. Hunt [1994] observed that larger chimps favored shorter trees, thereby minimizing the energy expended in climbing trees. The even larger body size of humans (compared to chimps or orangutans) also reduces our efficiency in harvesting fruit growing on the outer canopy of tall trees (where a substantial part of a tree's fruit is located), as our weight restricts us to relatively large branches. (Small branches could break, and falling out of trees certainly does not promote evolutionary survival.)

Temerin et al. [1984, p. 225] note that:

Arboreal travel is precarious at best, and increasing size makes compensatory demands for stability increasingly important. One response to this is to limit travel speeds.

The remarks of Aiello [1992, p. 44] provide further insight:

In larger animals, [tree] climbing can be two to three times more costly in energy terms than horizontal locomotion, a relationship that may explain why arboreality is largely confined to smaller primates. The obvious exception to this pattern is the arboreal orang-utan--the largest arboreal mammal with an approximate average body weight of 55 kilograms. It is, however, both highly specialized in its anatomy and fairly lethargic, climbing slowly and deliberately.

In summary, it seems quite odd that humans allegedly evolved to eat a nearly 100% fruit diet, yet our body size may be "too big" for an efficient frugivore, and we lack the major ape adaptations (quadrupedalism; hand and muscle adaptations) needed to efficiently collect fruit. That is, the fruitarian program alleging we are adapted to eat a diet of fruit lacks substantial awareness of the real-world needs of animals who eat high percentages of fruit to be able to efficiently collect that fruit. The obvious conclusion here is that the claim humans evolved as strict fruitarians is crank science (or, if you prefer, science fiction).

Fruitarian nutrition vs. brain evolution

Finally, the question of whether a fruitarian diet could supply the nutrition needed to drive brain evolution must be considered. All available evidence indicates that the answer is no. Some of the relevant reasons are:

Synopsis and Section Summary

We have seen that:

Comparative "proofs" that ignore intelligence and brain size are dubious. At this point it is appropriate to once again connect this section and the previous one to the topic of comparative anatomy. Two points are relevant here:


(Limitations on Comparative Dietary Proofs)

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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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