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Term Paper on Biology: Evolution of Primate Locomotion and Body Configuration

2021-07-12 14:42:51
8Ā pages
1944 words
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Wesleyan University
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Term paper
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Trees were once humans home, but this has changed over time as they have lost the adaptability to tree climbing partially due to evolution. The hands are still adaptable to tree climbing whereas the assimilation of bipedal walking has made the legs redundant in the arboreal. A lot of evolutionary evidence is seen in the locomotion and body configuration of primates. However, some of the changes are not readily visible and require in-depth scrutiny.

The Lemuroids

Madagascar is home to the strepsirrhines and lemurs with over thirty species represented and five families. As such, the size of the Lemur is up to a maximum of twenty-two pounds while the smallest weighs averagely 28 grams. Human activities and settlement have made some lemurs extinct that were found to weigh as much as 240kg. On consideration of evolution, the lemurs haven't undergone many changes in comparison to their descendants. This aids in comprehending of primates development as we can observe ancestral primates first hand.

The ring-tailed lemur is one of the most commonly known lemurs. Similarly, to other lemurs, locomotion is utilizing their four limbs quadrupedal, on both trees and the ground. However, the spine is designed and adapted to movement quadrupedally, they can hop on twos. There are some fossils from most primitive primates that have a way of living that is similar to the modern lemurs. Although they were not direct descendants of the lemurs in the sense of adaptation.

Nevertheless, the study of the spine of the lemurs shows that is different from that of other primates that position their back in an upright posture. It implies, all monkeys and other primates that walk on all fours almost entirely have a longer and more flexible spine. Making it difficult to maintain a vertical position. The locomotive behavior of lemurs is different as it can leap both horizontally and vertically their spine resembling that of quadruples and found clinging to tree trunks.

The Tarsiers

The Tarsiers belong to a single genus and one of the smallest primates commonly found in Southeast Asia. Moreover, they are nicknamed living fossils due to high resemblance to the primates that date past 40 million years. As such, this primate has enormous eyes in this order and is related to the night. The tarsiers have longer hind limbs than forelimbs with a long and virtually hairless tail. The tarsiers have pads on the edge of their fingers that are adapted to clinging and leaping. Additionally, the uniqueness of tarsiers is that they possess grooming claws on their second and third toe, unlike the lemurs that have toilet claws only on their second toe (Evans, Sarah, Nick, and Delia 162).

The possession of many first features that have become obsolete in much-evolved primates has made the strepsirrhines and tarsiers grouped. Although, the tarsiers also share some characteristics with the higher primates. An example of a bony structure that separates the eyeball from muscles involved in chewing, both lack a toothcomb, a nose that is dry and covered by hair, lips that are not divided, a short muzzle with reduced facial stubbles and the anatomy of the placenta (Evans, Sarah, Nick, and Delia 162). The examples indicate that the similarity between tarsiers and anthropoids is more as compared to that of strepsirrhines.

The movement of tarsiers can be compared to that of a frog and can leap from a small branch to another. For the tarsiers to perform this action swiftly the leg bones that is the tibia and fibula are conjoined at almost half-length enhancing the strength of the legs. The name tarsier is derived from the word tarsals which have an elongated ankle bone that also that help the animal leap efficiently (Evans, Sarah, Nick, and Delia 172). As an emphasis, tarsiers are carnivorous and feed on small lizards and small insects. The large eyes and grasping claws have played an essential role in the perpetuity of the tarsiers if not for the adaptable features they wouldn't have survived this long.

The Monkeys

There are different types of monkeys those that are arboreal and those that live in the grassland. The dimensions of monkeys range from five to six inches long inclusive of the tail. The mass can be as low as four to five ounces and reach up to seventy seven pounds. The environment in which the animals live gives them different characteristic and unique features to adapt to their environment for survival. Monkeys of the new world have a tail that gives them the ability to swing from one tree to another, while old monkeys have no prehensile tail or presence of tail at all (Reed, David, and Diekwisch 47). Some monkeys have three receptors in their retina for the perception of color otherwise referred to as trichromatic others are dichromatic and others monochromatic. Even though the new and old monkeys have eyes facing forward they have entirely different faces, however, they share characteristics such as nose and cheeks.

Moreover, the spider monkey is a unique kind as its evolution characteristics allow it to move in different ways. The spider monkey can run or walk on fours, while climbing, hanging and moving from one tree to another they use suspensory locomotion and bipedalism is used when leaping. Regardless, the monkey uses four limbs in movement especially when there are no obstacles, and the terrain is relatively even. When in suspensory locomotion they use their arms for mobility while ensuring that the tail holds (Reed, David, and Diekwisch 53). The tail of the spider monkey helps it to move bipedally acting as an external spine. The tail is also muscular and robust enabling it to act as an extra arm.

The Apes and Man

Apes and humans differ from other primates as they lack a visible external tail. As humans and apes begin to maintain an upright posture, it is believed that the physical outer tail starts to disappear. When the tail is lost the musculature is integrated into the pelvic surface, which forms an added support for the internal organs. The upright posture will make the organs move downwards. Notably, amongst all the primates man and apes are the most intelligent of all.

However, humans are more dependent on other animals for survival. Other than an external tail, the other difference is that humans and apes do not possess a useful appendix that is present in monkeys. Both belong to the Hominoidea family. Although, in recent times humans were classified into their own family. It was stated that humans were found to be different from apes in several aspects. However, a study on the fossils indicates that there are more similarities between humans and apes than thought earlier. Apes can be located in all of the worlds, Orangutans and Gibbons are ape species that are most commonly found in Southeast Asia. In Africa, there is gorillas, bonobos, and chimpanzees which are exclusive and only found in Africa.

The gibbons have 13 species, and one of the smallest apes otherwise referred to as lesser apes. They grow to a height of about 3 feet and weigh between twenty two to twenty pounds. The gibbons are adapted to their environment by possession of long arms that enable it to move from one tree to another with ease. They have curved fingers that allow them to grasp tree branches accurately. Their lightweight bodies also enable the arms to support the organization making the gibbons excellent brachiators. Gibbons can walk bipedally on top of branches although they are better swingers.

Furthermore, orangutans are the rarest type of apes and biggest commonly found in Southeast Asia. The orangutans can grow as tall as 4.5 feet and weigh up to 200 pounds. The large body mass inhibits the orangutans from swinging, therefore they must walk on land. Unlike other apes, they have a meaty upper part of their faces. The female orangutans can move from tree to tree due to their lighter structure (Maiolino, Stephanie, Kingston, and Lemelin 21). However not as swift as gibbons the female orangutans adjust their body weight from one branch to another as their way of brachiation. The large body size forces the primates to come out of the trees as their habitat and get more acquainted with land. The large body size does not favor being an arboreal.

The gorilla is the largest species in the ape family as it can grow to heights of about 6 feet tall and arm length of 10 feet. The long arms and emergence of knuckle-walking has seen the quadrupedal locomotive form face extinction and bipedal movement more acceptable and adapted (Maiolino, Stephanie, Kingston, and Lemelin 199). However, gorilla moves on fours since the legs are small and cannot support the massive head and thorax. The gorilla uses the sole of their legs in walking, but instead of the palm, the gorillas use the knuckles to support their large structure. Gorillas similar to humans are creatures of the ground and not arboreal.

The gorilla bears a resemblance to humans but not as much as the chimpanzees. The chimpanzees are termed as humans' cousins. Chimpanzees grow to a height of about 5.5 feet and an average body mass of 100 pounds. The arms grow to a length of 6 feet. Due to spine evolution in the primates, the chimpanzee is capable of walking bipedally but prefer to movement quadrupedally. For this reason, they are termed as humans' cousins.

Theories of Evolution

There are three theories that were formulated to explain the evolution of primates. The arboreal theory is one of the oldest theory that is used to explain the evolution process, and the other theory is visual predation theory and consequently the most recent theory the angiosperm radiation theory (Young, 128). The arboreal theory was accepted as the theory that explained the evolution of primates until it was questioned and other theories were proposed.

The arboreal theory states that the early primates evolved in such a way that it suited them to live an arboreal life. An example is since they lived in a three-dimensional environment they developed a full stereoscopic vision that created an enabling environment to interact with the environment. The orbit underwent orbital convergence a process that shifted the axes of the orbit from lateral to anterior facing spectrum enabling stereoscopic vision (Young, 118131). Increase in dependence on vision made the olfaction less reliable and therefore shortening of the snout. Grasping hands with nails instead of claws was another adaptation of the arboreal world.

There are counterarguments against the arboreal theory that states there are other orders other than primates that have species living in trees and none of them shows adaptation that is in primates. Squirrel and animals with limbs alike to that of squirrel both hind and fore limbs are better adapted to arboreal life with stronger support. Claws are better in going up and down trees as compared to nails that are present in primates. Certain arboreal mammals depict the significance of olfactory gesture in transmitting and receiving information (Williams, Scott, and Russo 27). This falsifies the theory of arboreal. Other arboreal does not show the signs of stereoscopic vision found in other primates. Moreover, the primate that has most orbital convergence is slow in nature.

Additionally, visual predation theory is another theory that seems like is expounding on the arboreal theory by stating that the orbital convergence that leads to stereoscopic vision, the hands, and feet that are adapted to grasping and reduced claws to fingers that have nails were adaptation of night-time searching for fruits and insects that were in the bushy layer of the jungle information (Williams, Scott, and Russo 37). Stereoscopic vision would aid in determining the distance of the prey without having to move the head a lot like in modern-day owls.

Angiosperm radiation theory is the weakest...

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