A comprehensive review of the scientific literature taking
a new look at an old subject grown musty with age.
and Physiology Brought Up to Date
Are Humans Natural Frugivores/Vegetarians,
by Tom Billings
Copyright © 1999 by Thomas E. Billings. All rights reserved.
Contact author for permission to republish.
A detailed TABLE OF CONTENTS linked to all portions of the article can be
found at the bottom of this first page of introduction.
An Invitation to Readers
If you are--or have ever been--involved in alternative diets or vegetarianism, you have probably heard or read claims that comparative anatomy and/or comparative physiology "proves" or (in more conservative language) "provides powerful evidence" that humans are "natural" fruitarians, vegetarians, or even omnivores. This paper will assess such claims and the evidence supporting them, but we first need to ask:
If these questions interest you, I invite you along for the ride. But first, open your mind and fasten your seat belt--the ride may be bumpier than you expect!
- Whether comparative anatomy and physiology provide actual hard proof of the precise composition of the "natural" human diet, or if they merely provide general indications of possible diets.
- Then, we want to go beyond the typical simplistic analyses presented in the vegetarian and alternative diet lore, and reexamine what information comparative anatomy and physiology actually provide regarding the natural diet of humans.
- Further, a number of related claims are often made as part of such comparative "proofs." Some of these claims addressed here are:
- Does "instinct" (whatever that is) "prove" that we are natural vegetarians?
- Does research that shows the typical Western meat-based diet is unhealthy prove that all omnivore diets are unhealthy?
- And, since it is mentioned in the subtitle, just what is a faunivore, anyway?
If your time is limited, or you have specific interests...
As this paper addresses numerous, diverse topics by necessity (some in depth), it is lengthy and this may present obstacles for some readers. Also, considerable background information must be covered before the main claims of the major comparative "proofs" of diet can be addressed.
To help navigate the numerous topics, to gain a quick bird's-eye view, or to read the paper in sections as time permits, the comprehensive Table of Contents below provides direct links to all the major sections and subsections of the paper.
T A B L E O F C O N T E N T S
- PART 1: Brief Overview: What is the Relevance of Comparative Anatomical and Physiological "Proofs"?
- PART 2: Looking at Ape Diets: Myths, Realities, and Rationalizations
- PART 3: The Fossil-Record Evidence about Human Diet
- PART 4: Intelligence, Evolution of the Human Brain, and Diet
- PART 5: Limitations on Comparative Dietary Proofs
- PART 6: What Comparative Anatomy Does and Doesn't Tell Us about Human Diet
- PART 7: Insights about Human Nutrition and Digestion from Comparative Physiology
- PART 8: Further Issues in the Debate over Omnivorous vs. Vegetarian Diets
- PART 9: Conclusions: The End, or The Beginning of a New Approach to Your Diet?
Brief Overview: What is the
Relevance of Comparative Anatomical
and Physiological Proofs?
Looking at Ape Diets--Myths, Realities,
DIETARY CLASSIFICATIONS AND WORD GAMESMANSHIP
THE EVIDENCE OF APE/PRIMATE DIETS
The Fossil Record Evidence
about Human Diet
Intelligence, Evolution of the
Human Brain, and Diet
- Introduction: claims of the comparative "proofs"
- Human intelligence ignored or rationalized
- Brain size discounted
- Hidden, contradictory views on the value of intelligence
- Recent evolutionary research now emphasizes the interaction of diet and brain development
- "Expected" vs. actual brain size
- Kleiber's Law
- Brain and digestive system compete for limited share of metabolic energy budget
- A comparative anatomy analysis of primate brains
- Humans at top of primate scale
- Large gap between humans and great apes
- Brain enlargement disproportional
- Factors in encephalization: energy (metabolism) and diet
- Extensive energy required for brain growth
- Dietary quality is correlated with brain size
- Dietary shift beginning with Homo
- How dietary quality relates to the brain's share of total metabolic budget
- Dramatic changes in last 4 million years
- Human brain's metabolic budget significantly different from apes
- Human brain MR (metabolic rate) 3.5 times higher than apes
- Humans depart from normal dietary quality (DQ)/body-weight relationship
- The paradox: Where does the energy for the large human brain come from?
- The relationship of dietary quality and gut efficiency to brain size
- Fruitarian evolution: science fact or science fiction?
- Vague claims about an ancient frugivorous primate ancestor
- Crank science and logical fallacies used in support of claims of fruitarian evolution
- Fruitarian denial of physiological evolution/adaptation
- Analysis of the fruitarian claims
- Claim: Morphological evolution is "easy," physiological evolution is nearly impossible.
- Claim: The digestive system is extremely complex. For it to evolve in a mere 2.5 million years is simply not possible.
- Claim: (twisted quote) Expert opinion is that physiological evolution is highly unlikely.
- Claim: There is no convincing teleonomy proof that humans have adapted to a diet that includes meat!
- Claim: There are no examples of animals evolving backwards from a vegetarian to an omnivorous diet!
- Claim: If humans are adapted to eating meat, what exactly are those adaptations?
- Further evidence against the claims of fruitarian evolution
- Quadrupedal vs. bipedal adaptations and tree-climbing/fruit-picking
- Actual fruit availability/dependability fluctuates with location and time
- Different adaptations, different tradeoffs
- Adaptations must be interpreted in context
- Body size and tree-climbing
- Fruitarian nutrition vs. brain evolution
- Vitamins, minerals, and fats
- Evolution/survival on pure fruit diets not possible in nature given fluctuations in fruit availability
- Synopsis and section summary
Limitations on Comparative
What Comparative Anatomy Does
and Doesn't Tell Us about Human Diet