The evolutionary process has altered the physical characteristics and behavioral characteristics of primates which led to the appearance of bi-pedal primates. There are several major physical differences between bipedal and non-bipedal primates:
Differences between bipedal and non-bipedal primates
A human skeleton (left) and a mountain gorilla skeleton (right)
In the illustration above, we see two skeletons: that of a human, and that of a mountain gorilla. Humans are obligate bipeds, meaning that they must walk on two legs, while the gorilla is a quadruped, walking on all fours (knuckle walking). The difference between these two modes of locomotion are reflected in the skeletal structure. Although the mountain gorilla is not the common ancestor of humans and the other great apes, we will use it's skeleton to make a general comparison between bipedal primates and non-bipedal primates.
Anatomical adaptations to bi-pedalism:
The foot:The foot of bipedal primates is evolved to carry the entire weight of the body. You can see from the gorilla skeleton that it's foot is very different. It is much wider, with more opposable digits for grasping limbs. Quadrupedal primates had flat feet while bipedal primates evolved ones that were more arched, to help with the distribution of weight and balance. Bipedal feet are also longer to facilitate efficient walking. Elongated structure transfers energy from the leg for the forward locomotion of the foot.
One of the most apparent differences between the legs of a bipedal primates and their quadrupedal relatives is length. Longer legs create a longer, more efficient stride. Quadrupedal legs are more bowed for clinging to trees. This shape is also better suited for squatting. Bipedal knees are enlarged to support more body weight.
Hips:
The hip socket of bipedal primates evolved to become larger, allowing it to bare more weight and have a wider range of motion. Their hips also moved closer to the spinal column to maintain upright balance with less effort.
As these primates began to walk upright, their spinal cord developed an 's' shape to prevent slumped posture and to place the center of the body directly over the feet.
Skull:
The skull of bipedal primates is set more directly on top of the spine where as the quadrupedal primates' spinal cord enters the back of the skull.
Correlation between bigger brain ratio and relationships
Behavioral adaptations to bipedalism
-Traveling long distancesThe evolution of true bipedal locomotion in hominids allowed for the evolution of a wide variety of new behavioral traits. First, true bipedal locomotion allows for far greater efficiency in walking long distances. Chimpanzees and gorillas can walk upright, but only with great effort and awkwardness. Secondly, bipedal locomotion frees up the arms and hands to perform a huge variety of tasks which a hominid perform. From fighting and hunting, to carrying food and infants over long distances, the free use of hands while walking would have presented hominids with many opportunities for advantageous behaviors.
-moving objects from place to place
The ability to carry objects over long distances could also have lead to a development of a new material culture. Non-bipedal hominoids would not have been able to move objects from one place to another with such ease. Freeing the hands during locomotion therefore allows for a greater development of material culture (the gathering of objects, collecting useful items or food etc.). This greater material culture, in turn, may have led to biocultural evolution.
Theories of the emergence of bipedalism in hominids
Paleontological evidence shows that bipedalism emerged very early in hominid evolution. Why some primates should have moved to bipedal locomotion is unclear. Paleoanthropologists have developed several theoretical scenarios that may have led hominids to evolve bipedal locomotion.
The first such theorist was none other than Charles Darwin. Darwin correctly assumed that the African apes were the closest living relatives to humans, and devised a scenario that he thought might explain the transition to bipedalism. Darwin's idea was that hominids were driven to evolve bipedal locomotion by a change in diet. Accordingly, early hominids changed to lifestyle of hunting with weapons and eating meat. This would have required a freeing of the hands to carry weapons and meat. This change to eating meat, according to Darwin, may have happened concurrently with a change in habitat - a loss of tree cover.
It appears that there is a basic problem with this scenario: paleontologists have found that early hominids all lived in areas that were partially or fully wooded. If bipedalism arose in a forested environment, then Darwin's model will not work. Other models have been proposed. One postulates that strong but optional bipedalism arose while our ancestors were still in the trees. In this scenario, hominid's ancestors were already walking horizontally along tree branches before they came out of the trees. One piece of evidence in favor of this hypothesis is the fact that our nearest living relatives, chimpanzees, bonobos, and gorillas, are all capable of bipedal locomotion for short distances.
Other scenarios have been proposed, including changes resulting from the use of weaponry in inter-hominid competition, climate change and other factors. One theory holds that early hominids evolved bipedalism as a result of a change in social behavior, in which males were travelling to gather food and bringing it to females. This arrangement, called 'vested provisioning', may have provided the selection pressure to evolve bipedal locomotion. However, the current state of evidence does not point to any of these narrow scenarios as being the one correct evolutionary path that led to bipedalism.
Paleontological evidence shows that bipedalism emerged very early in hominid evolution. Why some primates should have moved to bipedal locomotion is unclear. Paleoanthropologists have developed several theoretical scenarios that may have led hominids to evolve bipedal locomotion.
The first such theorist was none other than Charles Darwin. Darwin correctly assumed that the African apes were the closest living relatives to humans, and devised a scenario that he thought might explain the transition to bipedalism. Darwin's idea was that hominids were driven to evolve bipedal locomotion by a change in diet. Accordingly, early hominids changed to lifestyle of hunting with weapons and eating meat. This would have required a freeing of the hands to carry weapons and meat. This change to eating meat, according to Darwin, may have happened concurrently with a change in habitat - a loss of tree cover.
It appears that there is a basic problem with this scenario: paleontologists have found that early hominids all lived in areas that were partially or fully wooded. If bipedalism arose in a forested environment, then Darwin's model will not work. Other models have been proposed. One postulates that strong but optional bipedalism arose while our ancestors were still in the trees. In this scenario, hominid's ancestors were already walking horizontally along tree branches before they came out of the trees. One piece of evidence in favor of this hypothesis is the fact that our nearest living relatives, chimpanzees, bonobos, and gorillas, are all capable of bipedal locomotion for short distances.
Other scenarios have been proposed, including changes resulting from the use of weaponry in inter-hominid competition, climate change and other factors. One theory holds that early hominids evolved bipedalism as a result of a change in social behavior, in which males were travelling to gather food and bringing it to females. This arrangement, called 'vested provisioning', may have provided the selection pressure to evolve bipedal locomotion. However, the current state of evidence does not point to any of these narrow scenarios as being the one correct evolutionary path that led to bipedalism.
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