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:
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).
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
.