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.]
APPENDIX: Further Evidence
The
following information is taken from The New York Times, May 15, 1979. According
to Dr. Alan Walker, a Johns Hopkins University anthropologist, Homo Erectus, the
species immediately ancestorial to our own Homo Sapiens, had evidence of an omnivorous
diet. Every Homo-Erectus tooth found was that of an omnivore. However, a small
sample of teeth from the human-like species during a 12 million year period leading
up to the Homo-Erectus period, indicates the earlier species may have been a fruit
eater. Even if this species, way before our own, lived on a fruit diet, they probably
would not have consumed what we consider typical fruits. Hundreds of plants produce
fruits that are tougher, more substantial foods than what we eat today.
Quoted
from an editorial by William Clifford Roberts, M.d., Editor-in-Chief of the American
Journal of Cardiology:
"When we kill animals to eat them, they end up
killing us because their flesh, which contains cholesterol and saturated fat,
was never intended for human beings, who are natural herbivores."
Quoted
from "WHAT DID OUR ANCESTORS EAT?" in Nutrition Reviews, by Stanley
Garn, Professor of Nutrition and Anthropology, and William Leonard, Assistant
Professor of Human Biology:
"These people of Upper Pleistocene, and
later those of the mesolithic, were our immediate ancestors, no longer hunters
exclusively and with whole-grain products and a variable amount of roots, fruits,
leafy vegetables and nuts in their diet. We must grant them a mixed diet, with
animal fat providing a smaller proportion of their food energy than was probably
true for the Neanderthals."
This article was originally published in
the May/June 1991 edition of the Vegetarian Journal, published by:
The Vegetarian
Resource Group
P.O. Box 1463, Dept. IN
Baltimore, MD 21203
(410) 366-VEGE