Survival and Success of Bipedal Primates

Survival Issues:

• the need to find new food and water sources after the thinning of the forests took place 
• the threat of very large, roaming predators 
• increased exposure to the sun 
• increased difficulty in birth and raising of young due to longer maturation periods

Physical Characteristics that helped/hurt bipedal primates facing these issues:

Helpful Traits:

Bipedalism

The most important factor in the switch to bipedalism is the freeing up of the hands. A change in locomotion and how this species got around also made them more stable walkers and even developed into the ability to run. Bipedality was helpful in finding food because it allowed primates to see over longer distances on the savanna and the bipedal stride helped them expend less energy when walking long distances foraging for food and water. Becoming migratory could have been new to these bipeds, and introduced them to the potentiality of traveling around and surveying new landscapes with better food sources. Traveling longer distances could have helped these species avoid predators, as their bipedality made them less effective at escaping danger. Standing upright also made it easier to get food from low hanging tree branches. A standing posture made them appear bigger and more threatening as well.

Bipedalism also reduced the amount of sun exposure these primates were experiencing since they no longer had their backs toward the sun. As the the forests began thinning during this time, the intensity of the sun could have become much greater. The need to be able to release body heat is common in every animal, and is typically done through panting. As humans, we do not pant. We release body heat through sweat glands located under the surface of our skin. It is possible that the development of these sweat glands is what allowed for the loss of hair that we begin to see in these species.


A Precision Grip

It is thought that Homo habilis was the first of the bipedal primates to begin perfecting the use of tools. It is obvious that this is not a characteristic that developed overnight, but one that took time and patience. As the bipedal primates began to use tools, their hands began to change. They developed longer and stronger thumbs due to the pressure applied to it while using tools. Also, their fingers became more flexible and dexterous. These better grasping and manipulating hands allowed them to use tools to fight predators (like throwing stones) and meant they were better at handling those tools to protect themselves. The beginning of tool use possibly led them to begin cooking their food, though we are not sure when this took place. Cooking was very important to the success of these species, as it allowed for a much higher caloric intake without a high energy expense.


Omnivorous Diet

The ability to process different types of food effectively was probably one of the most important evolutionary adaptations that took place in bipedal primates. When their diet began to include more meat, it led to the evolution of smaller, sharper teeth and a more slender jaw, better for processing this wider range of foods. Those with flatter teeth were better suited to process plant foods. As they began to eat meat and other sources of protein, whether it be from scavenging or hunting, it paved the way for encephalization. It is thought that due to the change in diet, the temporal lobes and the prefrontal cortex of these primates began to grow disproportionate to the rest of their brains. This is important because the temporal lobe controls communication skills, while the prefrontal cortex is responsible for complex decision-making and social behavior. Another important change in the bipedal primates diet was the addition of starch. Studies on the saliva of humans versus the saliva of chimpanzees show that humans produce an enzyme called amylase, which breaks down starch into sugar, while chimpanzees and other animals do not posses this quality.

Impeding Traits:

Bipedalism

A possible disadvantage to bipedalism is the loss of the ability to climb. The development of bipedality meant primates developed stronger legs and weaker arms which made it increasingly harder to live in trees. The changes in foot structure made it difficult to grasp, causing more problems surviving or finding shelter in an arboreal environment. This put them in more danger because bipedal primates were slower at running from quadrupedal predators and could no longer use the trees to escape.

Encephalization

The growth of large brains could have been an impeding quality in that birth became much more difficult and dangerous. It also made the raising of offspring a slow and difficult process due to the long maturation period required to finish the development of the brain.