Introduction

Little is known about the evolutionary beginnings of primates. The best earliest fossil evidence puts primate origins back about 55 million years ago (mya).  The best known earliest primate form is known as Aegyptopithecus dated to about 34 mya. From the fossil remains, we know this was a quadraped that lived in an aboreal environment and was the size of a small dog.

From about 23 mya to 10 mya, emergence of apes moden looking dentition and by15mya, modern looking ape jaws, and face structures. At about 12 mya, a noticeable increase in the amount of ground dwelling species of apes with larger molars, suggesting a diet that included hard vegetable foods, including nuts.
 

Gigantopithecus (7 mya to 300,000 years ago) a giant fossil ape found in China, Viet Nam and Northern India. It had huge jaws and teeth, and is estimated to have stood between 10 and 12 feet tall. Dental evidence suggest that Gigantopithecus was a vegetarian like the modern-day gorilla. Certain features and teeth link it to the sivapithecid group

Primatology is a subfield of physical anthropology that combines field observations of primate behavior, and the study of primate anatomy. As such, it's both an observational and an experimental science. The study of primate anatomy and behavior allows us to identify traits that are shared between humans and primates and therefore are derived from a common ancestor.

Primate Ecology
Primates today tend to occupy three specific types of environments:
i. Tropical Rainforests
ii. Deciduous Tropical Forests
iii. Open Savannah-Woodland Environments

Each setting presents specific challenges to primates who seek food and water, while at the same time avoid predators, disease, and parasites. As a result, many primate species have developed specialized diets and or food acquisition strategies that compliment the environments in which they live. Thus, when we talk about primate ecology, we are talking about the relationship that exists between primate behavior and anatomy, and the external environment.

Most primate species operate on a very tight energy budget. If energy expended exceeds the energy obtained by the animal in the environment, then the animal dies. Any energy surpluses the animal might gain are extremely important because they can be applied to behaviors that increase the fitness (ability to survive and successfully reproduce offspring) of the animal.

a) Nutrition - How a primate feeds itself will determine what ecological niche it occupies in nature, and the anatomical features most closely associated with primate feeding systems include the teeth, bones of the jaw and skull, lips, cheeks, and various muscle masses which allow for chewing.

b) Locomotion - The relationship between locomotion and habitat is variable due the fact that all primate species are capable of a range of different locomotive patterns, postures, and gaits (locomotive profile).

d) Senses and The Brain - The development of sensory organs and brains of differing sizes appears to be related more to evolutionary heritage and less to ecological adaptation. Brain size in primates is relatively important in the organism's ability to acquire, store and retrieve information. Vision is often reflected in the size of the eye orbits of the skull, and is directly correlated with patterns of feeding.

The Evolution of Primate Societies
Much of the recent work done in field primatology stresses the study of individual groups over extended periods of time, and this approach has shown the extreme complexity of most primate social groups. Extended fieldwork has allowed primatologists to identify "individuality" among primates such as Chimpanzees. It is this range of different personality types that makes the patterns of interaction between individuals very complex.

Why Do Primates Interact Socially?
Many primatologists feel that since primates expend a lot of energy in social interaction, it must serve some adaptive purpose. As a result, like locomotion and feeding systems, many of the basic patterns of primate social behavior are shared traits that have been inherited from a common ancestor.

Primate Communication includes a variety of mechanisms, including:
a) vocalizations and cries
b) facial movements and body gestures
c) swelling of sexual organs
d) scent

More primitive primates such as lemurs tend to communicate by leaving scent marks along the branches and tree trunks that they travel. More advanced primates, such as the Great Apes, rely more on vocalizations, facial gestures and body gestures to communicate.

Social interactions allow primates to live in structured groups. Living in groups provides primates with a number of adaptive advantages, including:
a) foraging efficiency
b) defense of territories
c) decrease in energy expenditures
d) increased opportunities for care of offspring

Primates tend to structure their relations with others in terms of either: antagonistic behavior and hedonistic behavior.  Antagonistic, including threats and attacks (usually males) establishes dominance. Hedonistic behaviors, such as grooming, provide a "social currency" for favors and preferential treatment.

Reproductive Strategies
In order to maximize their "fitness" males need to develop strategies that allow them to mate with as many females as possible. Aggressive Male behavior provides a context in which males can compete among each other for mates. Female Reproductive Strategies increase their "fitness" by channeling all of their available energies into parental care for their offspring.

Sociobiology argues that natural selection favors behavioral traits that enhance the survival or reproduction of single individuals. Group Selection argues that natural selection favors behavioral traits that enhance the survival or reproduction of groups of individuals.

The Great Apes
Given the fact that at least some of the behaviors we express as humans are similar to those expressed by Great Apes, anthropologists are extremely interested in understanding how social behavior among great apes might resemble the behaviors expressed by our earliest hominid ancestors.
 

Orangutans are unique among great apes in that they are not socially gregarious. Rather, most individuals live solitary lives in the jungles of Southeast Asia. While males and females are highly territorial, their home territories overlap to provide them with breeding opportunities.

Chimpanzees are the most socially gregarious of the Great Apes. Chimps live in groups that form and disband in relation to the interactions of their members. Females tend to breed within the population in which they are born and often forage by themselves in ranges that overlap with those of other females. Unlike other primate species, mating is generally not an aggressive and competitive procedure. As a result of this general lack of sexual aggression, there is very little sexual dimorphism present between male and female chimps, and little in the way of large canine teeth, etc.

Gorilla social organization is the opposite of chimps. Gorillas are not socially gregarious, instead they live in small groups comprised of females jealously guarded by a single male. This has lead to marked sexual dimorphism between male and female Gorillas. Gorilla foraging territories are quite small, reflecting the abundant in the environments that they usually inhabit.

Early Hominid Analogies
Since human beings are genetically most closely related to Chimpanzees, (98.5% genetic similarity between our species) it seems likely that some aspects of chimp social behavior may have characterized early hominid behavior. Attempts to understand human social-cultural evolution have also been made by examining human hunter-gather groups. This has been done under the premise that the least technologically complex human societies may parallel the life of our hominid ancestors, since they made similar ways of living. The use of these kinds of analogies has to be taken with some caution however, since foraging peoples are fully modern people, and not the pre-modern versions that we are trying to understand.

By comparison, there are some intriguing similarities between foraging societies and societies of non-human primates, particularly with chimpanzees and bonobos.  Specifically, there are similarities in mother infant bonds, the presence of a home range, group social dynamics, and the role of cooperation within groups.  Since humans have been foragers for most of the time that we have been on earth, it seems reasonable that the behavior of our earliest ancestors was not that different.

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