Essay, Research Paper: Primate Evolution


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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.

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