Chapter 8
Primate Models for
Human Behavioral Evolution
Chapter Outline
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Introduction
Human Origins and Behavior
Brain and Body Size
Language
The Evolution of Language
Primate Cultural Behavior
Chapter Outline
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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
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(a) Chimpanzee and (b) Human. Anatomical
differences arise through changes in regulatory
genes in one or both species.
Human Origins and Behavior
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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
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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
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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
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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
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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
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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
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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
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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
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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
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The bonobo Kanzi, as a youngster, using lexigrams to
communicate with human observers.
Question
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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
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Vervet monkey communication includes
specific sounds for different
categories of predators (air, tree or
ground).
Lateralized
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Pertaining to lateralization, the functional
specialization of the hemispheres of the
brain for specific activities.
Motor Cortex
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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
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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
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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
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The language area of the brain that is
responsible for speech production is
Broca's.
Primate Cultural Behavior
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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
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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
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(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
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Chimpanzees in
Bossou, Guinea,
West Africa, use
stones as hammer
and anvil to crack oilpalm nuts.
The youngster is
learning to use stone
tools through
observation.
Criteria for Cultural Acts in
Other Species
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Innovation
New pattern is invented or modified.
Dissemination
Pattern is acquired by another from an
innovator.
Criteria for Cultural Acts in
Other Species
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Standardization
Form of pattern is consistent and
stylized.
Durability
Pattern is performed without presence
of demonstrator.
Criteria for Cultural Acts in
Other Species
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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
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Nonsubsistence
Pattern transcends subsistence.
Naturalness
Pattern is shown in absence of direct
human influence.
Anthropocentric
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Viewing nonhuman organisms in terms of
human experience and capabilities;
emphasizing the importance of humans
over everything else.
Core Area
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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
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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
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Behavior that benefits another individual
but at some potential risk or cost to
oneself.
The Primate Continuum
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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.