Comparative Anatomy and Physiology Brought Up to Date

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T A B L E   O F   C O N T E N T S   F O R

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PART 5
Limitations on Comparative
Dietary Proofs

• Introduction

• Logical and structural limitations
  • Comparative "proofs" of diet are subjective and indeterminate; i.e., they do not provide actual proof of diet
    
    • Four "proofs"--but what do they prove?
      
  • There is no logical validation for the implicit assumption that comparing two or more species via a list of features constitutes proof that a particular diet is natural or optimal
    
    • How are features chosen for a comparison list?
    • Once a feature is selected, how to measure?
    • What is the definition of a "match"?
    • How many matches are required for "proof"?
  • The comparative "proofs" focus only on similarities while ignoring differences
    
    
  • The comparative "proofs" ignore the fossil record and evolution
    
    
  • The comparative "proofs" are dated and do not reflect current knowledge of ape diets
    
    
  • The comparative "proofs" assume dietary categories are discrete (distinct), while in nature diets form a continuum
    
    
  • The comparative "proofs" ignore the important features that make humans unique in nature
    
    
  • Comparative "proofs" assume the form/function connection is strict and necessary
    
    • Similar functions can be served by dissimilar forms
      
    • The form/function relationship can be dissimilar even in closely related species
      
    • Overall systemic constraints as important as individual functions/forms
      
  • Research on the form/function linkage
    • Early research
      
    • Gut morphology
      
    • Mastication
      
    • More reliable insights by limiting complexity and narrowly defining features to be studied
      
  • The same form can serve multiple/different functions
    
    • Canine teeth
      
    • Primate teeth
      
    • Teeth of hominids
      
  • Subtle changes in form can produce or support significant changes in the function of organs or body systems
    
    
  • The function served by a particular form can vary dramatically according to specific feeding behavior
    
    • Coprophagy
      
    • The surface area of the digestive system may be less important than the retention time of food in the gut
      
  • Analysis of dietary adaptations is non-trivial
    
    • Evolutionary adaptations are compromise solutions that reflect the effect of multiple selection pressures, applied simultaneously
    • Diets can temporarily change with habitat in the same species
      
    • Staple foods vs. critical but more rare foods
      
  • Phylogenetic (structural) challenges in comparative studies
    
    • The form of digestive features can be affected by non-diet factors
      
    • Difficulty of untangling cause and effect

• Counterexamples to the paradigm of comparative proofs of diet
  
  • Polar bears: an example of semi-aquatic feeding behavior
    
  • The giant panda: a "carnivore" on a bamboo diet

• Section summary

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

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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