FREE ESSAY ON DIET AND PRIMATE EVOLUTION

DIET AND PRIMATE EVOLUTION

Diet and Primate Evolution
Variation in the choices of food on a daily, seasonal, and yearly basis is one of the
greatest differences between primate species. Primate diets have generally been divided
into three main food categories-fruit, leaves and fauna (including insects, spiders, and
bird's eggs for the most part). The different diets also are referred to as Frugivores,
Folivores, and Insectivores (fruits, leaves and insects respectively). These gross
dietary categories are correlated with aspects of primate activity patterns such as home
range and group size. There are different problems that have to be overcome in order to
obtain a balanced diet on a day-to-day basis. New leaves and mature leaves, for example,
may have different nutritional bases or availabilities. Some fruits appear in large
clumps while others are spread thinly over a larger area. Aside from diet, primates have
tended to either adapt through specialized dentition and digestive systems or rely on a
variety of different foods. Those that chose this second route have tended to have larger
brain sizes relative to their overall body size. This may be due to the need to know
where different types of food can be found at different times throughout the year. 
Have you ever looked at a picture of a gorilla or money that has what appears to be a
beer belly look? Those primates that specialize on eating large amounts of vegetation
have difficulty digesting their meals. Different solutions have been found including
double stomachs or multichewes, but the problem usually requires an individual to sit
back and let the digestive system work-and on the die expel gas.
It hasn't been until recently that it was realized that primates, who evolved in the
canopy, actually had a quite difficult time finding adequate nutrition. Due to natural
selection, which strongly favors those traits enhancing foraging efficiency, and this
difficulty finding sustenance, the characteristics regarded as belonging to primates were
evolved.
Most primates species either maximize the efficiency of their digestive track or maximize
the quality and the volume of food processed in a day. Also. Those species, which
increase the volume of food, consumed also tended to have larger brains because of a need
to remember, not only what, but also where good food sources are and when they are in
season. 
Knowing the trends of evolution, the next thing to do is to look at how it relates to
humans. It can be seen that out closest living relative, the chimpanzee makes up 94% of
his diet with plants. Most of this is fruit with high sugar and fiber content, meaning
that chimps take in hundreds of grams of fiber per day; contrary to the 10 grams or less
the advantage American consumes. This suggests that our diet should be higher in vitamin
C, pectin, and fiber like our relatives in the wild. Ironically, the same natural
selection, which favors the most energy-dense and low fiber diets, may now be causing us
to suffer from too little fiber. 
Plants have been a major food eaten by primates. The primates were almost exclusively
herbivorous. A strong focus on plant foods is characteristic of all primates-- and there
is strong consensus that the primates were very strongly herbivorous (Milton 1987, 1993).
Many plants are lacking vital nutrients, such as vitamins and the protein building blocks
known as amino acids, that the monkeys and other animals require. Some plants lack enough
carbohydrates to make them worthwhile as energy producers. Yet in all of these cases the
primates would still search for specific plants that exhibited one or more of these
traits, rather than just rely on the plant life that was within easy reach. 
The fact that the primates would make an active search from a variety of plants. One
particular type of plant may have lacked was often complemented by the positive aspects
of another plant. For example, fruits are low in fiber and protein and yet they are rich
in valuable carbohydrates. If the primates had relied solely on eating fruit then they
would have lacked sufficient protein and vital amino acids. To make up for that
particular type of shortage, the monkeys eat certain leaves that are high in protein and
fiber and that are also more abundant than the fruit. Together, the fruit and the leaves
make for a much balanced diet for the primates. 
In order for the primates to rely on just one particular type of plant as a food source,
the primates would have to travel quite a distance to obtain enough food from multiple
trees of the same plant type. In addition, trees of a certain species tend to produce
fruit or leaves during specific seasons of the year and then they are either without
fruit or possibly without leaves. If primates were to depend on a single source of food
supply, either fruit or leaves, then they would have to starve while waiting for a new
crop of fruit or leaves to grow. With a varied diet, the primates are able to eat
different plant types year round, and get a complete set of nutrients too.
A tremendous diversity exists within the dietary choices of primates. As a general rule,
small animals require a high nutrient flow but a lower caloric input, while larger
animals can survive on a poor quality, high-density diet. This is linked to metabolic
rate, whereby the smaller the primate, the faster the metabolism (Gaulin and Konner
1977). Diet can also be associated with energy levels. It is notable that gorillas and
oranges exhibit low energy levels and consume low quality foods, while active chimpanzees
consume a high-quality diet. There are exceptions to the generalization that small
primates will select a high quality diet, while larger primates will rely primarily on
low quality foods. Aye-ayes consume a large proportion of insects in their diet and are
considerably larger than most other primate. Yet, they do eat wood boring insect larvae,
which are less mobile and provide a higher yield. As well, the potto consumes a high
proportion of insects and sap. This may somehow be linked to a faster metabolic rate
(Gaulin and Konner 1977). Dietary constraints, such as competition, should also be
considered. Natural selection would favor variation in size and the ability to exploit
alternative dietary niches. One such paleontological example focuses on the early horse
or equid. Ancestors of the contemporary horse were much smaller than today and consumed
shoots (growing plants) and fruits. Certain lineages established a trend towards grazing.
Within these lineages that exploited dense grasses (low nutritive value), an increase in
size, similar to modern populations, is evident (Gaulin and Konner 1977).
The primate gut is very sensitive to the differences between C3 and C4 plants.
Specifically, the microflora in human guts is sensitive to these differences. Human
primates can effectively digest fiber from vegetables such as cabbage and carrots, but
less
efficiently break down that from cereal fibers such as bran. This suggests that the
consumption of cereal grains is a recent departure from more traditional plant foods
consumed by a majority of primates.
Potentially, this is linked to an increase in energy requirements, with no increase in
dietary quality. The surface area of the small intestine must increase in order to
maximize
absorption of vital nutrients. Yet, the colon is actually a derived trait and not an
ancestral trait (Milton 1987).
Is there a primate analogue to the human gut? Quite similar proportions, with respect to
small intestine and small gut mass to body ratio, can be found in the capuchin monkey.
These monkeys have a high quality diet of rich foods such as fruits, oil rich seeds, and
insects. Baboons also have a very selective diet. Interestingly, both Savannah baboons
and capuchin monkeys are known for their manual dexterity, efforts in food preparation,
and extensive selective searching. The similarity in gut morphology is not associated
with a common ancestor, but more likely has arisen from commonality in high quality diets
(Milton 1987).
Dietary changes have been sited as the impetus behind bipedal locomotion. If early humans
exploited high quality, low-density foods, this would require a home base and extensive
travelling. Bipedalism could serve as a more energetically efficient method
for gathering food items. Based on her discussion of the capuchin monkeys, Savannah
baboons, and the use of the hand, Milton (1987) appears to support this hypothesis.
Extinction of robust australopithecines has also been linked to dietary shifts. Milton
(1987) suggests that robust australopithecines may have opted for a lower quality diet.
This is indicated by the massiveness in the morphology of dental and facial bones due to
consumption of tough plant foods. Such a dietary selection may have led to the direct
competition preceding extinction. There is a decrease in cheek tooth size, thinning of
dental enamel, expansion of cranial capacity, and increase in body size. Factors such as
these confirm a dietary change,
potentially linked with a novel technology, social innovation such as sharing or
development of language skills, or both.
The study of primate diets is an important aspect of paleonutrition. Information gleaned
from research on primates has been linked to such diverse topics as the anatomical
proportions of the human digestive tract, to the advent of language and bipedalism.
Although some connections are somewhat tenuous, primate studies can provide a living
perspective on the direction of human evolution.
There's a link between the diet and teeth. The typical of most primates lack of dietary
specialization. They tend to eat a wide assortment of food items. The teeth are not
specialized for processing only one type of food, a pattern corrected with the lack of
dietary specialization. 
Most primates possess fairly generalized teeth. For example, the cheek teeth have low,
rounded cusps. Equipped with this type of premolar and molar morphology, most primates
are capable of processing a wide variety of foods ranging from rough or hard items, such
as leaves and seeds, to more easily processed fruits, insects, and even meat. 
Although the majority of primate species tend to emphasize some food items or others,
most eat a combination of fruit, leaves, and insects. Many obtain animal protein from
birds and amphibians as well. Some (baboon and, especially, chimpanzees) occasionally
kill and eat small mammal, including other primates. Others, such as African colobus
monkeys and the leaf-eating monkey (langus) of Southeast Asia, have become more
specialized and subsist primarily on leaves.