Introduction
There are a number of popular myths about
vegetarianism that have no scientific basis in
fact. One of these myths is that man is naturally
a vegetarian because our bodies resemble plant
eaters, not carnivores. In fact we are omnivores,
capable of either eating meat or plant foods. The
following addresses the unscientific theory of man
being only a plant eater.
Confusion between Taxonomy and Diet
Much of the misinformation on the issue of man's
being a natural vegetarian arises from confusion
between taxonomic (in biology, the procedure of
classifying organisms in established categories)
and dietary characteristics.
Members of the mammalian Order Carnivora may or
may not be exclusive meat eaters. Those which eat
only meat are carnivores. Dietary adaptations are
not limited by a simple dichotomy between
herbivores (strict vegetarians) and carnivores
(strict meat-eaters), but include frugivores
(predominantly fruit), gramnivores (nuts, seeds,
etc.), folivores (leaves), insectivores
(carnivore-insects and small vertebrates), etc.
Is is also important to remember that the relation
between the form (anatomy/physiology) and function
(behavior) is not always one to one. Individual
anatomical structures can serve one or more
functions and similar functions can be served by
several forms.
Omnivorism
The key category in the discussion of human diet
is omnivores, which are defined as generalized
feeders, with neither carnivore nor herbivore
specializations for acquiring or processing food,
and who are capable of consuming and do consume
both animal protein and vegetation. They are
basically *opportunistic* feeders (survive by
eating what is available) with more generalized
anatomical and physiological traits, especially
the dentition (teeth). All the available evidence
indicates that the natural human diet is
omnivorous and would include meat. We are not,
however, required to consume animal protein. We
have a choice.
The Great Apes
There are very few frugivores amongst the mammals
in general, and primates in particular. The only
apes that are predominantly fruit eaters (gibbons
and siamangs) are atypical for apes in many
behavioral and ecological respects and eat
substantial amounts of vegetation. Orangutans are
similar, with no observations in the wild of
eating meat.
Gorillas are more typically vegetarian, with less
emphasis on fruit. Several years ago a very
elegant study was done on the relationship between
body size and diet in primates (and some other
mammal groups). The only primates on the list
with pure diets were the very small species (which
are entirely insectivorous) and the largest (which
specialize in vegetarian diet). However, the
spectrum of dietary preferences reflect the daily
food intake needs of each body size and the
relative availability of food resources in a
tropical forest. Our closest relatives among the
apes are the chimpanzees (i.e., anatomically,
behaviorally, genetically, and evolutionarily),
who frequently kill and eat other mammals (including other primates).
Evidence of Humans as Omnivores
Archeological Record
As far back as it can be
traced, clearly the archeological record
indicates an omnivorous diet for humans that
included meat. Our ancestry is among the
hunter/gatherers from the beginning. Once
domestication of food sources began, it included
both animals and plants.
Cell Types
Relative number and distribution of
cell types, as well as structural specializations,
are more important than overall length of the
intestine to determining a typical diet. Dogs are
typical carnivores, but their intestinal
characteristics have more in common with
omnivores. Wolves eat quite a lot of plant
material.
Fermenting Vats
Nearly all plant eaters have
fermenting vats (enlarged chambers where foods
sits and microbes attack it). Ruminants like
cattle and deer have forward sacs derived from
remodeled esophagus and stomach. Horses, rhinos,
and colobine monkeys have posterior, hindgut sacs.
Humans have no such specializations.
Jaws
Although evidence on the structure and
function of human hands and jaws, behavior, and
evolutionary history also either support an
omnivorous diet or fail to support strict
vegetarianism, the best evidence comes from our
teeth.
The short canines in humans are a functional
consequence of the enlarged cranium and associated
reduction of the size of the jaws. In primates,
canines function as both defense weapons and
visual threat devices. Interestingly, the
primates with the largest canines (gorillas and
gelada baboons) both have basically vegetarian
diets. In archeological sites, broken human
molars are most often confused with broken
premolars and molars of pigs, a classic omnivore.
On the other hand, some herbivores have
well-developed incisors that are often mistaken
for those of human teeth when found in
archeological excavations.
Salivary Glands
These indicate we could be
omnivores. Saliva and urine data vary, depending
on diet, not taxonomic group.
Intestines
Intestinal absorption is a surface
area, not linear problem. Dogs (which are
carnivores) have intestinal specializations more
characteristic of omnivores than carnivores such
as cats. The relative number of crypts and cell
types is a better indication of diet than simple
length. We are intermediate between the two
groups.
Conclusion
Humans are classic examples of omnivores in all
relevant anatomical traits. There is no basis in
anatomy or physiology for the assumption that
humans are pre-adapted to the vegetarian diet.
For that reason, the best arguments in support of
a meat-free diet remain ecological, ethical, and
health concerns.
[Dr. McArdle is a vegetarian and currently
Scientific Advisor to The American
Anti-Vivisection Society. He is an anatomist and a
primatologist.]
Source: The Vegetarian Resource Group.
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