Ironically, our greatest achievement as a species
may be applying our enlarged brain and our technology to recreating the
diet we instinctively ate a million years ago.
by Sally Grande and Stephen Leckie
Imagine the primordial jungle. Imagine many kinds of
primates, including anthropoids (chimps, gorillas and early humans)
foraging for fruits and protein-rich leaves in the canopy of the arboreal
forest. This story begins more than 55 million years ago but it has been
the life-long study of Dr. Katherine Milton,
professor of anthropology at the University of California. Her quest for
links between diet and evolution is shared by David Popovich, a doctoral
student in nutritional sciences at the University of Toronto, who also
sees a connection between diet and human development of vision, depth
perception, memory, speech, dexterity and social behaviour.
We have been given the impression that our early
ancestors were closer to carnivores than they were to plant eating
animals. The degree of meat in the early hominid diet is a matter of
controversy and the more conservative view sees evidence for including
small amounts of meat in the ancestral diet through opportunistic foraging
and scavenging. The ancestors in question lived long before any modern
human predecessors. The National Geographic Society's recent report on
Neanderthal life in glaciated Europe, for example, cites evidence of
cannabilism and reliance on hunting for food. However, these primate
cousins were relatively recent in hominid history. Our original ancestors
predate them by eons, long before the last great ice age. The early
hominids were much more similar to modern day chimpanzees and gorillas.
Most of us think of a chimp's life as being fairly
carefree. Dr. Milton was surprised when she was observing a troupe of
chimps and noticed that, instead of sitting around in the tree branches
and eating what was nearby, they hurriedly sought out specific foods,
rejecting a number of delicious looking leaves in order to move on. When
they found an acceptable specimen, they did not gorge themselves. Instead,
they seemed driven to obtain a mixture of fruits and leaves from a variety
of plant species. On the spot, Dr. Milton decided to devote her career to
studying how these animals met their nutritional needs.
Chimps in the wild today face many challenges to
obtaining a sufficient variety of plant material - similar challenges were
likely faced our distant ancestors. For starters, many plants have
developed outer coatings to discourage hungry herbivores. These outer
layers contain chemical compounds that taste terrible and sometimes are
lethal.
In addition, the fibrous content of plants, which we
call "fibre" or "roughage," resists breakdown by mammalian digestive
enzymes. Excessive intake of fibre is troublesome because when fibre goes
undigested, it provides no energy for the feeder. The trick is to do a
better job of digesting the fibre. At the University of Toronto, David
Popovich has been studying the micro-nutrient content of the wild
vegetation consumed by gorillas. He has found that much of the energy and
nutrient value that gorillas are able to derive from such a diet comes
from colonic fermentation. Their studies on human subjects have shown that
humans may also be able to rely on colonic fermentation. Thus, a diet
consisting of substantial quantities of fruits, vegetables and nuts - no
pasta or starches - will provide adequate protein, B-12 and amino acids
(the building blocks of protein). Gorillas and chimpanzees have little
trouble digesting cellulose thanks to the presence of the ciliate
Troglodytella in their intestines. However, chimps and gorillas in
captivity begin to lose their Troglodytella when they are fed cooked food.
Thus, it is reasonable to assume that humans lost their intestinal cilia
when they started cooking with fire.
While the amount of meat consumed by our distant
ancestors is still debated, there is consensus that the Pleistocene diet
consisted overwhelmingly of vegetable material.
Another concern with such a diet is finding time to
forage. Primates cannot concentrate on just a few plant sources because,
even if the fibre could be well-digested, many plant foods are low in one
or more of the required nutrients, such as vitamins or amino acids. Fruits
tend to be rich in easily digested forms of carbohydrate and relatively
low in fibre, and provide little protein. Given that primates in the
arboreal canopy do not cultivate protein-rich beans and vegetables, they
rely heavily on efficient access to a wide variety of preferred fruits and
leaves to achieve adequate protein.
Developing a better memory for the exact location of
favoured trees, the shortest routes between them and a timetable for when
they would likely be fruit-bearing would definitely favour survival. A
larger brain would no doubt support these activities as well as group
communication. Today, spider monkeys comb the forest for fruit by dividing
into small, changeable groups. Their expanded mental capacity helps them
recognize members of their own social unit and learn the meanings of
different food-related calls.
The inherent complexities of the plant food niche could
have been a factor in increasing the longevity of primates. Neither apes
nor humans can rely on their relatively poor senses of taste and smell to
detect toxicity, so they require several years of adolescence to learn
which foods are safe and nutritious. This may be why humans are one of the
longest living animals on earth.
Dr. Milton claims that the crafty Homo sapiens were
better equipped to solve the dietary problems wrought by changing
environmental conditions. Expansion of brain power in combination with
growth in body size and reduction in the jaw and teeth, are evidence of
achievement of a high quality diet. Without the high quality diet, the
increased body size simply produces a slow moving, fairly sedentary and
unsociable ape, like present-day orangutans and gorillas. Dental patterns
among fossils of hominids support evidence of a high quality, plant-based
diet. The decreased mass of the jaw and teeth signify that either our
ancestors were eating less fibrous, easier-to-chew foods or they were
processing them to remove material that would be hard to digest.
Some researchers have proposed that modification in
dental structures resulted partly from specialization in hunting and
scavenging. However, electron microscope examination of bones collected
from early hominid sites reveals that our ancestors most likely scavenged
bones that were already ravaged by carnivores. While the amount of meat
consumed by our distant ancestors is still hotly debated, there is
consensus that the Pleistocene diet consisted overwhelmingly of vegetable
material. While chimpanzees are known to kill, this behaviour is not
necessarily dietary but ritualistic and their diet is at least 94% plants
and fruits.
Wild chimps take in 100 grams of fibre each day, much
more than the 10 grams or less that the average North American ingests
today. Dr. Milton's studies have shown that the chimpanzee gut is
strikingly similar to the human gut in the efficiency with which it
processes fibre. According to Dr. Milton, our digestive tract does not
seem to be greatly modified from that of the common ancestor of apes and
humans, which was undoubtedly a predominately herbivorous animal.
While there is no authoritative recommendation for the
daily intake of fibre, the small amount ingested daily by most Canadians
is far less than we need to remain healthy. According to David Popovich,
captive gorillas are dying in zoos of the same arterial sclerosis
afflicting human cardiac patients because the zoos are unaware of the
gorillas' reliance on fibre. Dr. David Jenkins, known as the father of the
"fibre movement" in Canada and Director of the Clinical Risk Factor
Modification Centre at St. Michael's Hospital, continues to make a strong
case for vegetarianism as the optimum human diet.
Bibliography:
2002 Hans Dehmelt.
What is the
optimal diet of the anthropoid primate homo sapiens?(212 Kb pdf file)
Department of Physics, University of Washington, Seattle, March 18, 2002
1993 Milton, Katherine. "Diet
and Primate Evolution," Scientific American, pp. 86-93.
1996 Popovich, David. Interviews with graduate researcher in the
Department of Nutritional Sciences at the University of Toronto to prepare
this article (May, 1996).
1997 David G. Popovich, David J. A. Jenkins, et all. "The
Western Lowland Gorilla Diet Has Implications for the Health of Humans and
Other Hominoids." The Journal of Nutrition, Vol. 127, No. 10
October 1997, pp. 2000-2005.
1988 Potts, Richard. "On an early hominid scavenging niche."
Current Anthropology, 29(1):153-155.
1984 "Home bases and early hominids." American Scientist, 72:
338-347.
1988 Shipman, Pat. Scavenging or hunting in early hominids: theoretical
framework and tests. American Anthropologist, 88(1): 27-43.
1984 Stalh, Ann A. Brower. "Hominid dietary selection before fire." and
Adrian Kortlandt, "Commentary," Current Anthropology 25(2):
151-168 .
Source:
http://www.veg.ca
