Chapter 8

Primate Models forHuman Behavioral Evolution

Chapter Outline• Introduction• Human Origins and Behavior• Brain and Body Size• Language• The Evolution of Language• Primate Cultural Behavior

Chapter Outline• Aggressive Interactions Between Groups• Affiliation, Altruism, and Cooperation• The Primate Continuum• New Frontiers in Research: Molecular

Applications in Primatology

Developmental Changes in the Skull of Chimpanzees and Humans

• (a) Chimpanzee and (b) Human. Anatomical differences arise through changes in regulatory genes in one or both species.

Human Origins and Behavior • In the 1970s, the theory was that early

hominids diverged from apes as they moved out of a forested environment and adapted to a savanna environment.

• They were subjected to increased predation pressure, so they adopted bipedalism partly out of the need to stand upright while looking for predators.

Human Origins and Behavior• The evolutionary story of early hominid

ancestors probably began with a behavioral shift to exploiting an econiche different from other hominoids.

• This adaptation required spending more time on the ground.

• These factors, in turn, selected for further adaptations, while other hominoids were responding to different environmental pressures.

Human Origins and Behavior• Primatologists still use nonhuman primate

behavior to examine the evolution of human behavior, they also use statistical tests to examine relationships between variables. They look for correlations between life history

traits and sociality. Once correlations are found, they can

propose principles to the study of human behavioral evolution.

Brain and Body Size• One characteristic that differentiates humans

from other species is relative brain size. • The relationship between body and brain size is

the index of encephalization. • Modern humans have a brain size well beyond

that expected for a primate of similar body weight, a central component of recent human evolution.

Brain and Body Size• Early members of the genus Homo as

well as more primitive hominids (Australopithecus) weren’t nearly as encephalized as modern humans are.

• Allometry, also called scaling; is the differential proportion among various anatomical structures.

Cortex• In the brain, the cortex is the layer that

covers the cerebral hemispheres, which in turn cover more primitive or older structures related to bodily functions and the sense of smell.

• It’s composed of neurons which communicate with each other and send and receive messages to and from all parts of the body.

Neocortex• The more recently evolved portions of the

cortex of the brain that are involved with higher mental functions and composed of areas that integrate incoming information from different sensory organs.

Comparisons of Mammalian Brains

Language• Nonhuman animals haven’t been

considered capable of communicating about external events, objects, or other animals.

• It has been assumed that nonhuman animals use a closed system of communication, where vocalizations don’t include references to specific external phenomena.

Language• These views have been challenged:

Vervet monkeys use specific vocalizations to refer to categories of predators, such as snakes, birds of prey, and leopards.

Other studies have demonstrated that numerous nonhuman primates produce distinct calls that have specific references.

Language

• The bonobo Kanzi, as a youngster, using lexigrams to communicate with human observers.

Question• Vervet monkey communication

a) is used to support the theory that primate vocalizations do not include external events or objects.

b) is limited to scent marking and an occasional bark.

c) includes specific sounds for different categories of predators (air, tree or ground).

d) is sophisticated with regard to food.

Answer: c• Vervet monkey communication includes

specific sounds for different categories of predators (air, tree or ground).

Lateralized• Pertaining to lateralization, the functional

specialization of the hemispheres of the brain for specific activities.

Motor Cortex • That portion of the cortex involved in

sending outgoing signals involved in muscle use.

• The motor cortex is located at the rear of the frontal lobe.

Left Lateral View of the Human Brain

• Information that is to be used in speech is sent from Wernicke’s area, via a bundle of nerve fibers, to Broca’s area.

Evolution of Human Language

Question• The language area of the brain that is

responsible for speech production is:a) the left hemisphere.b) Broca's.c) Wernicke's.d) Cerebellum.

Answer: b• The language area of the brain that is

responsible for speech production is Broca's.

Primate Cultural Behavior• Cultural behavior makes primates attractive as

models for behavior in early hominids.• Since humans are products of the same

evolutionary forces that produced other species, they exhibit some of the same behavioral patterns.

• Because of increased brain size and learning capacities, humans express many characteristics to a greater degree.

Primate Cultural Behavior• Cultural behavior is learned; it’s passed

from generation to generation not biologically, but through learning.

• Like young nonhuman primates, human children acquire a tremendous amount of knowledge through observation rather than instruction.

Culture is Learned• (a) This little girl is

learning how to use a computer by watching her older sister.

• (b) A chimpanzee learns the art of termiting through intense observation.

Using Tools• Chimpanzees in

Bossou, Guinea, West Africa, use stones as hammer and anvil to crack oil-palm nuts.

• The youngster is learning to use stone tools through observation.

Criteria for Cultural Acts in Other Species• Innovation

New pattern is invented or modified.• Dissemination

Pattern is acquired by another from an innovator.

Criteria for Cultural Acts in Other Species• Standardization

Form of pattern is consistent and stylized.

• Durability Pattern is performed without presence

of demonstrator.

Criteria for Cultural Acts in Other Species• Diffusion

Pattern spreads from one group to another.

• Tradition Pattern persists from innovator’s

generation to the next.

Criteria for Cultural Acts in Other Species• Nonsubsistence

Pattern transcends subsistence.• Naturalness

Pattern is shown in absence of direct human influence.

Anthropocentric• Viewing nonhuman organisms in terms of

human experience and capabilities; emphasizing the importance of humans over everything else.

Core Area• The portion of a home range containing

the highest concentration and most reliable supplies of food and water.

• The core area is frequently the area that will be defended.

Territory • The portions of an

individual’s or group’s home range actively defended against intrusion, particularly by conspecifics.

• Members of a chimpanzee “border patrol” at Gombe survey their territory from a tree.

Altruism• Behavior that benefits another individual

but at some potential risk or cost to oneself.

The Primate Continuum• Human brains are larger than primate brains,

but the neurological processes are functionally the same.

• That humans are part of an evolutionary continuum is the basis for animal research, yet we cage nonhuman primates without regard for their needs.

• Nonhuman primates should be maintained in social groups and introduced to habitat enrichment programs.