How can we explain the survival and success of bipedal primates?

What are/were the survival issues?

The main survival issues of the past were disease, starvation, dehydration, war, and successful reproduction.

What traits may have helped survival (physical and behavioral characteristics)?

A particularly important trait in regards to the survival of primates is their bipedal pelvis and locomotion. Primates and humans have a tendency towards walking upward. Humans have a bipedal pelvis and therefore, walking upright on two legs is the way humans effectively move. Primates can move in bipedal motion as a result of their specialized pelvis, which allows for such a specific type of movement (Jurmain pp 122).

Another factor in the survival of primates is in regards to their movement as a result of their generalized limb structure. A generalized limb structure in primates and humans allows for various forms of locomotion using all of the limbs. Primates can move in different ways based on their skeletal structures (climbing, swinging in trees, etc.) while humans mainly walk on two feet. Humans and primates alike do have a generalized use of their limbs in order to function based on various situations (Jurmain pp. 122).

Primates and humans have prehensile hands and feet. Humans and primates can meticulously manipulate objects with their five-fingered hands and feet. This differs from other mammals as primates and humans exhibit a much higher level of control over objects with their hands and feet then all other mammals. Both have opposable thumbs and partially opposable big toes. Humans have nails on their fingers and toes instead of claws. Primates also have nails on all of their fingers. Every species of primate has nails instead of claws except for New World monkeys (Jurmain pp. 123). This is crucial to the degree of digital manipulation that primates can accomplish (Dr. Chipley’s Lecture).  Also, all lemurs and lorises have a claw on one digit. Both have tactile pads with fingerprints and nerve endings at the end of their digits. The fingerprints and palm prints allow primates and humans to more successfully hold onto things (branches, anything that is held). The increased sensitivity at the end of the digits in primates and humans assist in safety and manipulation of things with the hands and feet (Jurmain pp. 123).

A primates diet is of crucial importance in their survival because of its versatility. Primates do not have a specialized diet. Primates and humans have the ability to eat and metabolize plants and meats. Both have generalized dentition. This means that their teeth are not specialized for any one type of food (Jurmain pp. 123-124).

Another factor of survival is in the primates' visual abilities.

Primates and humans rely on their vision in order to live. They both have color vision, although nocturnal primates do not. Both also have stereoscopic vision, which allows for depth perception. Visual information in humans and primates is transmitted to both hemispheres of the brain. This allows for more detailed visual information. This information is organized into three-dimensional images by specialized structures in the brain (Jurmain pp. 124-125).

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The neocortex in a primate’s brain is essential in their survival because it allows for different senses and a more advanced sensory system.

Humans and primates have a decreased reliance upon the sense of smell. The olfactory glands (allow for smell) in primates and humans are smaller than they are in other mammals. This occurs because of the higher dependence that primates and humans have on their sense of sight. Some primates do have large noses for the purpose of accommodation for canine teeth or to attract mates.

Both have an increased complexity of their brains. This is most evident in the visual and association areas of the neocortex (part of the brain that allows for more advanced thinking). Humans have larger, more complex brains although the structures are quite similar in both humans and primates (Jurmain pp. 125-126).

The fetal nourishment in primates and humans is far more efficient than that of other mammals. Both have longer gestation periods (humans have longer gestation periods). They also have fewer offspring compared to other animals.  Both primates and humans have delayed rates of maturation and extension of their entire lifespan. Humans live much longer than other primates although primates live for a relatively long amount of time in comparison with other mammals (Jurmain pp. 126).

Humans and primates have a greater dependence and flexibility on learned behavior. This occurs because of their delayed maturation, which causes longer periods of infant and adolescent dependency on at least one parent. Because of this, the parents in both humans and primates invest more in their offspring. As a result both offspring receive more intense parental care (Jurmain pp. 126).

Humans and primates have a tendency to live in social groups.  Primates differ in that the males in the groups are permanent associations within social groups. Nocturnal primates tend to have smaller social groups. Humans have various sizes of social groups (Jurmain pp. 126).

Each of the above traits are important separately and in tandem with one another. These traits have allowed for primates to survive and become more adept at survival than other species.