Module 5: Primate Diet and Digestion


Primate Diet & Digestion
In this module we will explore the evolutionary basis of the human diet by looking at research and information about non-human primate diet and digestion. This information, while inferential, provides a basis for the way many researchers attempt to reconstruct human foodways in the past and evaluate our current diet and eating habits. The reading selections as well as the activities will highlight a number of fundamental issues such as hypotheses about the importance of meat in the human diet and how our diets and biology may be linked to our primate heritage.


1. To gain a general understanding of different primate diets.

2. To gain a general understanding of the factors which have shaped primate diets over time.

3. To understand the biological, behavioral and anatomical adaptations primates have for obtaining and processing food.

4. To be able to compare the digestive system of different primate species and understand the relationship between diet and digestive system form and function.

5. To be able to compare the human digestive system and diet with that of other primates and gain a better understanding of the kinds of diets for which the human gut is adapted.
Module 5 Gallery

Power Point Presentation (Soon to be posted)


Working in your group and using material from the web and readings do the following:

1. Using the information provided in the readings, on the module site and on the web prepare a short teaching lesson for the rest of the class comparing the digestive system of the one of the following sets of animals: (The specific set will be assigned in class)

  1. Human, chimpanzee, dog
  2. Colobus monkey, cow, human
  3. Baboon, human, dog
Notes – Introduction to Nutritional Anthropology
We are members of the Primate Order — first primates originated over 65 million years ago. Some of the very basic aspects of our physiology that relate to dietary adaptations can be traced to our primate heritage.
Types of Diet Found among the Primates:

Omnivore- generalist

Omnivore – eats many different types of food•Most (90%) eat at least some fruits & young leaves.

• Over 30% get some flesh/eggs/insects eclectic (wide variety of foods)

•  Most are quite generalized (capable of eating a wide range of foods)

Folivore – leaf eater

Frugivore – fruit eater

Insectivore – insect eater
A major theory for the origins of Primates is that they coevolved with the Angiosperms — the flowering plants — in the Late Cretaceous period.

• Primates eat a wide range of foods, and are omnivorous, in general.

• Most eat at least some fruit

• Primates have evolved real preference for certain types of fruits (e.g. compared to sympatric fruit bats, birds, or squirrels) —

•    Primates often prefer medium-sized, ripe, sweet fruits (yellow, orange, red)

Tropical forest birds that often select larger, oilier fruits. Smaller birds go for smaller fruits and berries.
Coevolution/ relationships with Angiosperms:

The Plant’s Dilemma:

Seeds produced by the plant need to survive and be dispersed.

Mechanical Solution: expensive !

  • Anatomy/ morphology: spurs, spikes, hard internal covering
  • “Flooding the market” – high production – eg. Figs

Chemical Solution: cheap!

  • Attract seed dispersers with fleshy fruit covering (or oil-rich aril)
    • sugars!
    • oils!
  • Protect seed from predation with chemicals “secondary compounds”
    • TOXINS (like Alkaloids = bitter taste)
    • digestion inhibitors (Tannins = astringent taste)
    • block enzyme function (trypsin inhibitors in legumes)

(n.b. secondary compounds are a relatively cheap way for plants to avoid predation)
“The Omnivore’s Dilemma”


1. biological/ physiological adaptations:

Detoxification in digestive system

2. Identification of dangerous substances:


a. Color vision (diurnal; distinguish ripe fruits & flowers)

Sense of smell reduced (dry nose and no whiskers)

b. Taste = ways of learning about the foods
Conditioned taste aversions/preferences (includes cultural)


“BITTER” = extremely sensitive to compounds common in toxins (e.g. alkaloids)

PTC = phenylthiocarbamide: taster polymorphism


Culturally, we have also learned to PROCESS plants containing secondary compounds in ways that mitigate or eliminate the deleterious effects

3. Dental Adaptations:

Teeth – responsible for initial processing – may also have non dietary function

Cheek Teeth: molars and premolars

break up food mechanically and prepare it for additional processing.

Insectivore –

Folivore –

Frugivore –

Omnivore (nuts & seeds) –

4. Digestive System Adaptations:

Quick Review:

  • While some enzymes in saliva begin breaking down carbos, most simple carbohydrate digestion / energy absorption takes place in small intestine
  • Most mechanical breakdown of food into small particles occurs with tools, teeth or in the stomach
  • Stomach acids can break down some muscle tissues and enzymes break down peptide bonds in proteins (more about this next time). Sacculated stomachs isolate the bacterial fermentation from the normal stomach function
  • Bile acids and salts (e.g. detergents) help break down lipids in the colon and fatty acids are absorbed through cells lining the colon.
  • The caecum is a chamber attached to the colon where hind-gut fermentation can take place, and is very large in many hind-gut fermenters. Note that the human appendix is essentially a vestige of the primate caecum

Digestive Strategies: FERMENTATION = extracting energy from fiber

  • Fore-gut fermenters = “Ruminants” (cows), kangaroo, Colobines & Indrii
  • Hind-gut fermenters = most mammals…

Proportion of Energy from VFA”s (Volatile Fatty Acids = fermentation):

Ruminants: Hind-Gutters:

Cattle = 75% Pig = 15%

Sheep = 68% Human = 1-10%

Digesting Fiber in hind gut is proportional to retention time and length of gut… bigger body sizes digest fiber more effectively… (e.g. gorillas!)
Katie Milton: Digestion of food represents a compromise between 2 conflicting demands:

1) efficiency of nutrient extraction

retention of food maximizes extraction but reduces volume/unit time

2) food passage rate & food volume

rapid gut passage increases potential volume of food but reduces efficiency of nutrient extraction

Animal Gut Capacity Stomach Small Intestine Caecum + colon
Pig 28 litres 29% 33% 38%
Dog 7 litres 62% 24% 14%
Spider Monkey 28% 31% 40%
Howler Monkey 26% 35% 39%
Human 6 litres 17% 66% 17%

Other Evolutionary Questions:

1. Vitamin C Dilemma:

Ascorbic acid

Essential for survival, but only needed in small amounts.


Vit C deficiency (Scurvy):

Most mammals can synthesize Ascorbic Acid from a form of glucose, using an enzyme called L-Gulano-Lactone oxidase. This enzyme is ubiquitous throughout nature… suggesting evolved early in primitive forms of life.


  • humans and other primates
  • guinea pigs
  • Indian fruit-eating bat>
  • Edvented Bulbul (a frugivorous bird)

The inability to synthesize Vitamin C is a potentially lethal mutation, unless you live in a tropical forest and eat a lot of fresh fruit & vegetables, so this is an ancient evolutionary legacy.

Humans are dependent on Vitamin C = strong selection pressure!

Linus Pauling has extended this argument to claim that we need very large doses of Vit C

Frugivore – eats fruit

Foliovore – eats leaves


Herbivore – eats grasses (image not shown)



There are four primary tastes: sweet, salty, sour and bitter. The ability to distinguish these tastes enable us to evaluate food and make the critical choice – should we swallow it or spit it out.

  • Sweetness
  • Salty
  • Sour
  • Bitter

Our ability to distinguish the four primary tastes (sweet, salty, sour, bitter) depends on the taste buds which are primarily located on the surface of the tongue, however some can also be found on the inner surface of the cheeks, the roof of the mouth, and in the throat.

  • genetic variation in the number of taste buds, but not in the location of them on the tongue.
  • serve as the interface between chemicals dissolved in saliva and the sensory neurons
  • different regions of the tongue seem to have slightly different sensitivity

Taste circuit Image: click here

Discovery of Taste (Trivedi, B.  2012 Gustatory System: The Finer Points of Taste Nature:486 S2-S3)

Digestive Tract Information

The different diets of domestic mammals have associated anatomical, physiological, and behavioral implications. Locomotor anatomy and behavior are linked to diet, the nature of the digestive tract in the abdomen has implications for locomotion. Features of three types of digestive tracts are:

Canine digestive tract
•simple glandular stomach
•small cecum and simple colon
•small abdominal volume especially when fasted
•high protein diet

Ruminant digestive tract (cattle, sheep, goat, deer, etc.)
•huge stomach with four compartments (fermentation chambers and a glandular compartment)
•large cecum and coiled ascending colon
•large abdominal volume even if fasted
•rumen flora and fermentation products supplement a roughage diet
Equine digestive tract
•simple stomach (half glandular)
•huge cecum and ascending colon
•large abdominal volume even if fasted
•roughage diet requires a protein source (obtained via grain or coprophagy)