Effect of Environmental Conditions on Human Behavior and Development in the Past

Timothy Kent

ANTH 111 16

Title: Effect of Environmental Conditions on Human Behavior and Development in the Past.

Abstract: This paper will discuss and outline behavioral and developmental changes in human existence and the reasoning behind the formation of these new distinctions. Several changes in the human past that will be discussed are the change from walking on all four limbs to bipedalism, the greatly increased brain size in humans as compared to earlier humans and the creation of language and communication among earlier species. These distinctions will be investigated and specific reasoning behind their formation will be analyzed. I will also compare early hominids to modern Homo sapiens and explain particular factors that lead to their evolutionary changes. The Australopithecus afarensis, one of the earlier hominids, has a brain size of 500cc centimeters as compared to modern Homo sapiens who possess a brain size of more than 1350cc. The adaptation of bipedalism is also an important highlight of human evolution and there are many theories to explain its creation. Bipedalism may have been evolved over time due to changes in their environment and a necessity to walk upright and on two feet. This paper will try to outline the human past and provide anthropological evidence to support the evolutionary changes in human development.

It is a fundamental postulation that hominid evolution is directly correlated to the environment the species existed in. The term hominid refers to any member of the human family, Hominidae, and even more specifically, the genus Homo. The family Homindae consists of ancestors of modern humans and apes living today. (Foley 1995: 2) The fossil record of human evolution is incomplete, however human fossils can be traced back to millions of years ago. The family of humans has evolved greatly over time and is in part due to the effect of the environment on their behavior and development. The evolutionary changes most evident in the past have been the emergence of bipedalism, increased brain size, development of language, and creation of advanced tools. The reasoning behind the formation of these distinctions in human evolution has been studied and several hypotheses have been formulated. Not a lot of information is known about our human ancestors, but examining the fossil record can offer clues to why the Homo genus evolved the way it did.

The emergence of bipedalism in the family of Hominidae has been theorized to be due to the adaptation to the new life that man began to lead. However, many hypotheses have been formulated about what made humans stand up straight on two feet rather than being quadrapedal. The hypothesis that is widely supported and accepted by anthropologists around the world is that our ancestors began to walk on two feet largely because of environmental changes. The change that formed this new feature in ancient humans was a gradual process rather than an abrupt alteration of their lifestyle. The lifestyle new humans began to lead included hunting and gathering in large open grasslands rather than climbing and living in trees. The additional stress and pressure that this new lifestyle put on the human body forced them to construct a new means of locomotion. (Lynn 2002:393)

The earliest fossils recovered, that provide evidence of bipedal locomotion, existed in the genus Australopithecus. The Australopithecus existed approximately two to five million years ago, in Africa. The Australopithecus is not a direct ancestor of the Homo genus; nevertheless, they do share a common ancestor. The Australopithecus, now extinct, was a small bipedal ape whose fossils reveal clues to the development of bipedalism. The major structural evidence for bipedalism are the foramen magnum, occipital condyles being set forward, and the way the neck muscles append to the lower back. All of these features are necessary for balance in upright stance, however the inner ear bone structure suggests a partial bipedal motion. The bone structure of the inner ear suggests that the Australopithecus resembled chimpanzees and gorillas and did not possess full bipedal posture. (Evans 2004: 1-2) One of the earliest fossils of hominids discovered, nicknamed Lucy, belong to the Australopithecus afarensis. This fossil, excavated in Ethiopia, exhibits early stages of bipedal movement. The specific features examined on Lucy included the way the hip and pelvis are positioned. The basket formed by the pelvis provided balance for the weight of the upper body and the locking knee joint allowed for upright posture (Kottak 2004: 155-158, 164). This new formation of these bone structures were induced by selective pressures in the new environment hominids existed in.

The environment of early hominids played an important role in the evolution of bipedalism. The formation of bipedalism provides morphological and behavioral evidence for the difference between hominids and pongids. Pongids, in contrast to hominids, are anthropoid apes of the family Pongindae, which include the chimpanzee, gorilla, and orangutan. New tools, ways to gather and consume food, and ways of traveling were all maximized with bipedalism stance and locomotion. The upright posture was determined to be a more energetically efficient form of walking as compared to quadrapedalism. Additionally, the upright posture decreased sun exposure which kept early hominids cooler, which ultimately granted more energy for other uses. The earliest bipedal hominids only partially walked on two feet and continued their arboreal nature until full bipedalism increased the species' fitness. (Isbell and Young 1994: 393)

The lifestyle of human predecessors was based on the new formation of bone structures that allowed them to move bipedally. As hominids began to spend more time on two feet, they were now taller and able to scout and get a better view of their surroundings. In the hunting aspect of early hominids, bipedalism provided a huge advantage over quadrapedal predators because they were able to view a larger range of the area. The speed of these newly developed hominids increased greatly because of bipedalism, aiding in hunting and general hominid actions. An additional advantage of bipedalism is the ability to carry possessions in their two free limbs. With this new ability, early hominids became able to carry food, tools or other possessions for long distances. The freeing up of these two limbs once used for walking created new advantages and formed a wholly different way of life for humans. (Evans 2004: 2)

An alternate hypothesis formed was amalgamated into the name, "The Jolly/Rose/Wrangham Hypothesis." (Hunt 1993: 191) This alternate hypothesis focuses on the importance of