The Evolutionary Developments of Primates

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One of the most fascinating aspects of life is that nature equips each species with the particular body configurations and locomotive abilities that can most effectively enable the species to survive. However, as species mutate and evolve, the members of a species tend to possess slight modifications to the normal characteristics. According to the concept of evolution and natural selection, when a member of a species possesses a characteristic that is favorable, the creature tends to utilize the beneficial trait to survive longer and reproduce more children. The children also most likely acquire the favorable characteristic, and as they survive longer and reproduce more and more children, each successive generation of the species features an increased number of members that possess the favorable characteristic until eventually, the trait becomes a dominant norm of the species. Because the human species is generally inferior to other animals regarding our smaller size, slower speed, weaker natural weapons, and weaker strength, it was essential that our species had the ability to adapt to changing environments and ascertain characteristics that improve our chance of survival. The body configuration and locomotion abilities of modern humans were generated by shared traits and the many different evolutionary developments and physical changes that modified the characteristics of primates.

The first grade of primates was the lemuroids, which included the lorises and galagos. Because there haven’t been many changes for lemurs over time, studying lemurs enables us to observe the physical, behavioral and locomotive characteristics of some of the earliest primates. The body configuration of grade 1 primates includes a long spine typically found in many quadrupedal primates that walk on all four limbs, for the long and flexible spines allow them to maneuver on all four limbs but prevent them from lifting their backs up to an erect posture (Hawk, 2011). Although the primary locomotive function of lemurs and grade 1 primates is quadrupedalism, the primates are also capable of using bipedalism to leap, as they can effectively jump from one location to another on two feet, and other primates would eventually evolve and develop this locomotive skill.

Lemurs and other grade 1 primates have prehensile hands, which enable them to perform the locomotive action of brachiation in which they are capable of moving through trees by gripping branches with their hands to continually swing from tree-to-tree. The body configuration of these primates also includes prehensile feet, which helped them grab objects, grip branches or lift food from the ground with their feet (Hawk, 2011). These grade 1 primates also features nails at the ends of their fingers and toes instead of claws, for nails helped them succeed while living in the trees by allowing them to dig the edges of the nails into tree limbs to more effectively maintain a sturdy grip on the branches while hanging, climbing or swinging on trees.

However, lemuroids also possessed a claw on their 2nd toe and a distinct tooth comb, which served the important locomotive function of enabling the primates to groom their fur. Many insects in forests can infest, irritate and contaminate fur, including ticks, lice, and fleas. Having their fur infested with insects and parasites exposed the primates to the risk of becoming infected with various diseases (Hawk, 2011). Thus, these primates developed the tooth comb and the claw on their 2nd toes because these devices provided them with the locomotive ability to effectively groom their fur and eradicate dangerous insects or pests.

The 2nd grade of primates from which our species evolved is the tarsiers. These primates had very tiny arms that were disproportionately small compared to their legs, which is a feature that would permeate for many other primate groups as well. These primates also possessed prehensile feet, but in contrast to a lemur, the tarsiers had two toilet claws, with one claw on the 2nd toe and an additional claw on the 3rd toe.

Tarsiers had prehensile hands to grip tree branches, as the primary locomotive function of the primates is brachiation and prehensile hands provided them with the ability to grip and securely hold branches to swing from tree to tree. However, studies indicate that these tarsier primates tend to be vertical clingers that can hang and remain suspended from tree branches for extended periods of time (Hawk, 2011). Thus, tarsiers developed padding on their fingertips so they could sustain their grips on branches and hang steadily from the branches for extensive lengths of time without experiencing pain or a diminished grip. Additionally, the tarsiers possess large hands and feet that can increase their ability to remain suspended from branches and that can improve their ability to effectively catch their prey. Because tarsiers are relatively small primates, they require large hands and feet to successfully subdue and capture their prey.

The body configuration of tarsiers having legs disproportionately longer than their arms was caused by exceptionally long ankle bones and two lower leg bones that become conjoined towards the bottom of the leg. Scholars assert that the longer features of the legs and leg bones helped serve the locomotive function of leaping, for the tarsiers were superior leapers that could leap from one tree to another with one thrust (Hawk, 2011). The long legs also enabled the primates to suddenly and abruptly leap out of bushes to attack and capture unsuspecting prey, which often consisted of smaller animals such as lizards and insects.

Because the primates consistently display the behavioral pattern of living nocturnal lifestyles, the body configuration of tarsiers also included very large eyes that enhanced their ability to detect and catch other animals at night. The difficulty of seeing at night makes them vulnerable to become attacked by predators, impairs their ability to prepare for the impending attack, and prevents them from being able to respond to the situation quickly. Thus, being awake and moving at night can be dangerous and expose them to the risk of potential attacks (Hawk, 2011). Additionally, in the darkness of night, it is harder to see prey and initiate attacks quickly enough to catch the prey before they can run or hide. However, the larger eyes enhanced the quality of the vision for tarsiers and enabled these primates to see at night effectively enough to spot prey, avoid predators, and flourish with their nocturnal behavior pattern.

The body configuration of tarsiers also has many similarities with anthropoids. For example, these primates did not possess toothcombs, they had a dry nose covered with hair, short snouts that contain minimal amounts of whiskers, and a unified upper-lip. Additionally, through an anthropological analysis, many cranial and facial features in the body configuration also demonstrate a connection between tarsier primates and monkey or ape primates.

The 3rd grade of primates includes monkeys, which are divided into the two classifications of old world monkeys and new world monkeys. Old world monkeys, or Cercopithecidae, consist of two subfamilies, Cercopithecidae and Colobinae, and each family demonstrates certain characteristics to indicate that the monkeys within each respective family share the same ancestral connection. Both families of Old World monkeys often display distinct sexual dimorphism that allows the observer to detect the sex of the monkey based on the stark difference in appearances between the two sexes. The Cercopithecidae family of old world monkeys tends to possess a buccal sack that they utilize for storing food, and although the monkeys are willing to eat a wide variety of different types of food, they generally prefer a diet that focuses on fruit. In contrast, the Colobinae family of old world monkeys typically fulfills a diet that emphasizes leaves (Jones & Pilbeam, 1992). This difference in dietary habits between the two different families is reflected in the different dental configurations of the monkeys, for Cercopithecinae monkeys tend to have rounded bilophodont molars with very large incisors, whereas Colobinae monkeys feature much smaller incisors but sharper teeth.

There are many differences between old world monkeys and new world monkeys. Although the body configuration of new world monkeys includes prehensile tails, old world monkeys do not display any tails. The prehensile tail of new world monkeys is often relatively muscular and very long, to the extent that some tails are longer than the body of the primates. In contrast to old-world monkeys, all species of new world monkeys are exclusively arboreal, almost always live in the trees and rarely forage on the floor of the forest. Thus, the possession of a tail is because new world monkeys require the strong prehensile tail to serve as an extra gripping device to grab and hold on to tree limbs (Jones & Pilbeam, 1992). Studies indicate that the tails were utilized to grip branches while suspending or brachiating among the trees and to grip the branches high up in trees so they can safely maintain their position while using their hands to eat food.

Another difference that separates the two classifications of monkeys is that new world monkeys have three upper and lower premolars on each side of their mouths, which aligns their dental configurations closely with the prosimians. In contrast, old world monkeys, apes and hominoids only have two dental premolars. New world monkeys also possess round and flat noses with forward-facing nostrils, which distinguishes the facial configuration of these primates from the noses and facial arrangements of old world monkeys and hominoids (Jones & Pilbeam, 1992). The monkeys tend to be mostly quadrupedal, as they typically walk on all four limbs, and the monkeys are also capable of brachiating, suspending, climbing and running. The monkeys are also capable of very impressive bipedal leaping.

Hominids and apes represent grade four of the primate evolutionary scale, and these primates also demonstrate the evolutionary transition that spawned the human species. Apes and hominids are different than every other type of primate because apes and hominids do not have external tails. Many studies indicate that the primates lost their tails for a variety of reasons. One reason is that the primates shifted their bodies into a more upright position, which over time caused the apes to lose their tails (Shapiro, 2001). After losing the tails, the musculature became incorporated into the pelvic floor to provide enhanced support for the organs that had shifted down as a result of the upright shift in body posture.

Another possible reason for the loss of the tail is that the large size of apes prevented some species from being tree-dwellers and instead caused the large apes to become terrestrial. Although many species of apes were still capable of brachiating and swinging among the trees, many species were far too large and heavy to be supported by branches and to maneuver successfully in the trees. Thus, large apes began to explore the flat terrestrial ground with much more frequency, and the departure from the trees diminished the need for the apes to possess prehensile tails or any tails at all (Shapiro, 2001). Having become obsolete and no longer required, generations began to feature less and less tails until over a vast stretch of time tails were entirely eliminated from the body configuration of apes and hominids.

An important evolutionary feature of apes is that many apes demonstrate the ability to periodically and briefly display bipedalism, which indicates that apes were among the earliest primates to possess this skill. Although they are primarily quadrupedal and usually must be on all four limbs to walk, the primates can effectively walk on two legs for temporary periods of time. While some apes are able to walk over short distances by balancing and moving on two legs, some other apes developed the strategy of dragging the knuckles along the ground to help maintain proper balance while walking on two legs. However, many early hominids were entirely capable of walking on two legs, and studies indicate that hominids typically utilized the skill of bipedalism when they were holding food or objects in both hands and needed to walk and transport the objects to another location (Zimmer). Thus, apes and early hominids represent the first traces of bipedalism from which our species absorbed the beneficial characteristic of walking on two legs.

Apes also feature a much more powerful intelligence level than the other primates, which is a characteristic that hominids and humans most likely absorbed as we evolved from the apes. Apes have a very large cranial capacity and a much more complex brain structure than the other primates, and the structure and capacity are most closely aligned with our own brains. For instance, apes have been proven to be impressively capable of displaying effective and complex communication skills, developing and utilizing tools to help overcome challenges, and demonstrating exceptional learning and comprehension skills. This high intelligence level is the most important aspect that enabled our own species to survive, for the size of the skull and brain continued to increase among the hominids, and the skull and brain size of humans is very large (Zimmer). Considering that we are inferior to many other species regarding our size, speed, weaponry, and power, the only feature that we have that is powerful enough to facilitate our survival is the mind and our superior reasoning skills. By exercising our high intelligence and powerful thinking skills, our early human ancestors were able to succeed in very difficult and dangerous hunts, utilize tools to build structures, and solve complex problems to maximize their chance at surviving very challenging circumstances.

Because hominids and the apes share a common ancestor that most likely resided approximately 5 to 8 million years ago, after splitting from the apes the hominids still retained some of the body configuration and locomotive characteristics that originated from the apes. However, over vast periods of time hominids and homo sapiens modified those characteristics to maximize our own survival capabilities.

One of the most important evolutionary developments of our species is the locomotive ability of bipedalism. Although apes initiated the skill with moderate and brief bipedal abilities, humans were able to actualize the full potential of bipedalism by becoming capable of standing, walking and running on two legs for long periods of time. The body configuration of hominids and homo sapiens became modified to further maximize our bipedal abilities, as hominids developed a recurved spine and a vertical backbone that allowed us to easily and comfortably maintain an upright stance, while other advancements in the hip joints and femurs of hominids further improved the bipedal ability of humans (Zimmer).

Additionally, the body configuration of hominids continued to evolve in ways that enhanced bipedalism. Hominids began to develop flat and arched feet along with very long legs that were disproportionately longer than the arms. The arched feet and disproportionately long legs helped improve the ability of hominids and humans to walk long-distances with greater endurance and to run short distances with faster speed (Zimmer). The ability to stand, walk and run on two legs was a very powerful evolutionary advantage, as the bipedalism enabled our species to more easily maneuver around diverse terrestrial environments, more conveniently carry and transport objects to appropriate locations, and more effectively use our hands to operate tools and build structures. Thus, the locomotive skill of bipedalism helped enhance the ability of our species to adapt and survive in various different environments.

Hominids also provided the human species with the essential evolutionary development of the opposable or prehensile thumb. The thumb originally developed with monkeys and apes, but the hominid species Homo habilis was the first known species that developed a prehensile thumb capable of enhancing the gripping abilities of the hands. Homo sapiens then inherited this body configuration adaptation and became capable of using the thumb to enclose our hands, fasten our fingers and tighten our grips on objects (Kemme, 2012r). This evolutionary development helped our species survive, for the prehensile thumb allowed us to attain firm grips on various objects, carry heavier objects such as tools and weapons, and maneuver our hands with more precise motor skills to grip tools and build various objects or structures.

Additionally, many scholars maintain that the proportions of the hands were molded over time to most effectively form a fist both for gripping objects and for fighting. The apes that hominids emerged from were very violent, and so too the hominids displayed substantial amounts of violence in the form of fighting rivals for mates or fighting enemy groups for resources. Because the ability to form a strong fist helped humans win fights, hold weapons and grip tools more effectively, humans that could form strong fists tended to survive longer and reproduce more children, which enabled the proportions of our hands and fingers to become most suitable for tight fist formation (Carrier, 2012). Thus, the human hand has relatively short fingers and a small palm along with a strong and flexible thumb, which provides us with the proportions required to form a fist, grip various objects and fight enemies.

Language is another evolutionary development that dramatically enhanced the survival capabilities of the human species. Although studies indicate that humans inherited the underlying necessary physical and mental characteristics that facilitate language from previous hominid groups, homo sapiens were the first to actualize the potential of complete oral language. Language required both body configuration changes and locomotive evolutions, and the primary types of evolutionary developments required for human language included neuro-cognitive, social and physical developments. Physical developments in the body configuration that allowed homo sapiens to use language include the increased size of the skull and brain, development of motor musculature in the vocal tract along with a neural circuitry that controls the musculature, and adjustments to the vocal tract, larynx and pharynx that allowed a resonant chamber to release audible speech sounds. Neuro-cognitive evolutionary developments that facilitated human language include a new connection between the cortex and vocalization locomotion, increasingly powerful memory, and the advanced mental ability to codify verbal symbols into words and associate meanings to those symbols (Kemmer, 2012, Language). Additionally, hominid social adaptations were also required to actualize the power of language, such as recognition and differentiation of others, listening to others and understanding the perceptions of others.

There were also many other body configuration changes that helped establish the appearance and locomotive functioning of the human species. Apes and hominid groups were generally the largest of the primates, and thus humans inherited the relatively large bone structures and body size from apes and earlier hominids. The body size continued to grow among hominids because larger sizes strengthened a creature’s power and enhanced its speed, which in turn improved the survival abilities of the creature and of the species (Zimmer). Humans also evolved to be very sexually dimorphic in that the physical differences between the sexes are dramatically noticeable.

Although apes had relatively dense hair to maintain warmth, reports indicate that the fur or hair of hominids continually became less and less dense until we homo sapiens generally discarded the majority of our hair. There are different valid theories that help explain why humans lost our fur. One theory suggests that early hominids left the forest and began walking across the blazing hot African deserts, and thus we lost our hair to help keep us cool during those hot walks. Another theory contends that humans lost our hair because dangerous parasites often infested and contaminated the fur of our primate ancestors with dangerous diseases, and thus we shed the majority of our fur to eliminate the threat of parasite infestations and to protect ourselves from becoming infected with diseases (Wade, 2003). Thus, natural selection most likely enabled humans to minimize our hair density to help us overcome the heat of the desert and to help us avoid parasitic infections.

During my visit to the Los Angeles Zoo, I was fortunate to get a very good look at a large group of chimpanzee apes. During my extensive and entertaining observation of the chimps, I was struck with awe at both the distinct differences and the close similarities between us humans and our ape ancestors. The glaring differences included the abundance of black fur that each chimpanzee possessed and the quadrupedal nature with which they walked around the grass and the rocks. Additionally, their body movements and gesticulations were very different, as their arms seemed to swing around with very lengthy and elongated movements. However, there were also many blatant similarities between us humans and the chimpanzees, and these obvious similarities made me reflect on how disingenuous it is for religious zealots to pretend that the notion of us “coming from apes” is so ridiculous and impossible. Just from looking at the chimpanzees it is apparent that the apes look very similar to humans, and the similar appearance definitely indicates an ancestral connection between the two species.

The aspects that appeared similar to humans included the rounded facial features, the primate body structure, and the arms, legs, hands, torso, and shoulders. Aside from the excessive fur, the general body configuration of the apes had an extremely close and direct resemblance to the body configuration of humans. Some of their locomotion patterns also reflected human motions, for the manner in which the apes would sit down, rest their elbows on their knees and look around the area with a ponderous and contemplative look on their faces provided the impression that these creatures were actually human.

I was very fortunate that I was eventually able to see bipedal locomotive functions. Although almost all of the dozen or more apes incessantly demonstrated quadrupedalism by walking on all fours, there was one moment in which a chimp stood on its two legs and quickly ran about ten feet over to a fellow ape, and there was another moment in which an ape exhibited a bipedal leap high into the air that was so unexpected that it surprised the entire crowd. Additionally, the social order of the chimpanzees was also similar to that of humans, for like humans some apes were walking around together while others were sitting in a circle together gathering, socializing and grooming each other’s fur. Thus, seeing living chimpanzees sitting and walking directly in front of me was an awe-inspiring experience that filled me with excitement to see animals so similar to us and appreciation for the source from which our species generated.

The human mind and body is a powerful combination that enabled our ancestors to overcome incredibly difficult circumstances and to survive an incessant array of challenges. For instance, the amazing fact that humans can use the mind to imagine new ideas that don’t exist and then use the body to transfer those ideas into the physical world and into existence has allowed us to invent tools, develop weapons, build shelters and develop clothing, all of which has enabled us to protect ourselves from threats and maximize our chances of survival. Although the body configuration and locomotive functions of humans effectively allow us to survive, it is important that we understand the history of our species, the evolutionary developments of primates, and how those developments helped to provide humans with the characteristics that we enjoy today.

References

Carrier, D. (2012, December 19). Fine Hands, Fists of Fury. University of Utah. Retrieved November 22, 2013, from http://unews.utah.edu/news_releases/fine-hands-fists-of-fury/

Hawk, J. (2011, October 12). Primate classification and phylogeny. John Hawks: Paleoanthropology, Genetics and Evolution. Retrieved November 21, 2013, from http://johnhawks.net/explainer/primates/primate-classification-phylogeny

Jones, J., & Pilbeam, M. (1992, July 15). Evolution of Old World Monkeys. NYCEP. Retrieved November 21, 2013, from http://pages.nycep.org/ed/download/pdf/Delson_1992.pdf

Kemmer, S. (2012, January 9). Primates: The Opposable Thumb. Rice University. Retrieved November 21, 2013, from http://www.ruf.rice.edu/~kemmer/Evol/opposablethumb.html

Kemmer, S. (2012, January 9). Language: Three Dimensions of Development in the History of the Human Species: Neuro-Cognitive, Social, and Physical. Rice University. Retrieved November 21, 2013, from http://www.ruf.rice.edu/~kemmer/Evol/dimensions.html

Shapiro, L. (2001, July 15). Primate Locomotion. PBS. Retrieved November 22, 2013, from http://www.pbs.org/wgbh/evolution/library/07/3/text_pop/l_073_08.html

Wade, N. (2003, August 19). Why Humans and Their Fur Parted Ways. The New York Times. Retrieved November 21, 2013, from http://www.nytimes.com/2003/08/19/science/why-humans-and-their-fur-parted-ways.html?pagewanted=all&src=pm

Zimmer, C. (n.d.). The Emergence of Humans. University of California Berkley. RetrievedNovember 21, 2013, from http://evolution.berkeley.edu/evolibrary/article/evograms_07