Brief on Human Evolution
All primates possess adaptations catering to an arboreal life-way as they are descended from tree-dwellers. For primates to adapt to live on trees, they first need to climb and achieve a series of complex motions on trees. Primates have opposable thumbs that are widely separated from other toes and fingers. The separation and opposed direction of the thumb lead to cooperation between the opposable thumb and other fingers. Such cooperation between fingers enables primates to firmly “lock” their bodies onto the tree branches. The way primates make a motion when they live on trees is by brachiating, that is, they swing by their arms. Not only does brachiation require a powerful grip achieved by the thumb cooperation, but it also demands a rotating shoulder joint to complete the motion of swinging. To swing from one point to another, primates need to be able to concisely calculate the distance between where they are and where they are moving toward. With their binocular vision, primates can achieve the stereoscopic vision and excellent depth perception which enables them to gauge the distance. The combination of this suite of characteristics results in excellent hand-eye coordination, on which primates rely to achieve physical motions living on trees.
Besides these three relatively important adaptations for dwelling in trees, other characteristics supplement primates’ arboreal lifestyle. For example, their claws have been modified into flattened nails; they have larger brains and greater brain/body ratio relative to other mammals so that their body can stay balanced on trees. Primates typically have one offspring per pregnancy which allows mothers to carry their babies with them while climbing trees by having their babies grip their uptight body.
According to fossil evidence, one group or species of apes living in Africa first left the trees and adapted to life in the savannas approximately 5 to 7 million years ago. Although we are not certain why this happened, popular theories assume that changes happened in the forest in which they lived. To survive in the mixed woodland grassland ecosystem where they no longer had many trees to swing on, those apes first needed to know how to walk upright on two legs, that is bipedalism. Some assume that bipedalism had to do with their need to see further through the grass, others say that it had to do with their needs of holding the food with their arms and sharing it with others. Although bipedalism doesn’t seem to immediately link with tool-making, tool-making is a primary characteristic of early humans without which the bipedal apes would not survive in the savannas.
This is because knowing how to make tools prepares bipedal apes to adapt by transforming their environment instead of physically changing themselves. Bipedal apes could have not evolved to be humans if they had not inherited their physical shape from primate ancestors. To make use of their physical shape and survive the transition of an environment from forest to savannas, a larger brain capacity enables is required. Additionally, it appears that increased brain size may have accompanied the development of tool-making and meat-eating. The increased brain size also impacts other aspects of human evolution. For a large-brained baby to pass through the birth canal of a narrow-hipped mother, baby needs to be born at an extremely early stage of development. Because the babies are born early, they are dependent upon society for a long time before they can mature and find themselves. During the period of dependency that is longer than other animals, babies acquire languages and culture.
Upon learning how to use tools, languages, and cultures, bipedal apes achieved the transformation into humans. The significance of this transformation is the establishment and development of languages, from which derived cultures and the concept of society that are necessary to human existence because they define what it means to be human. According to Darwin’s theory Descent with Modification, useful adaptations are passed onto descendants through heredity. With constant variation and modification on those existing adaptations, descendants can adapt to changing environmental conditions. The history of primates evolving into humans is a clear illustration of descent with modifications. With the inherited adaptations from primate ancestors of living on the trees, apes are able to sustain an arboreal lifestyle; and because of the inherited physical shape, those apes that later on left the forest and moved to savannas became bipedal. The bipedal apes continued to evolve and become humans with adaptations of languages and culture.
Works Cited
“The Evolution of Primates” Boundless.com, Lumen Candela, www.courses.lumenlearning.com/boundless-biology/chapter/the-evolution-of-primates/
Petersen, Glenn. Human Evolution. PDF file.
