AP Psychology Unit 2:
The Biological Bases of Behavior
(Chapters 2 and 4)
An Early History of Biopsychology
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Plato: the mind is
located in the brain
Franz Gall and
Phrenology
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Touch my sexy
head lumps. Go
on….touch them!
Early 1800s
Read bumps on skull
to understand traits
Biopsychology Today
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Everything we do is ultimately controlled by
our body and brain
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Body/brain composed of cells
Brain cells called neurons communicate
electrically and chemically
Different parts of the brain have specific functions
Our brains create meaningful experiences from
sensory information
Brain structure and function is influenced by
experience
Neurons: Defining and Types
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A NEURON is a nerve cell.
There are three basic types of neurons (diagram):
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Sensory Neurons: Afferent neurons that detect stimuli from
sense organs and relay this information TO the brain and/or
spinal cord.
Motor Neurons: Efferent neurons that receive signals from the
brain and/or spinal cord and relay this information to glands
and muscles.
Interneurons: neurons in the brain and spinal cord that
coodinate activity between sensory and motor neurons.
Three Types of Neurons in action!
Glial Cells: provide nutrients to neurons, insulate
neurons, and remove debris when neurons die.
Neuroanatomy (diagram)
The Neural Impulse (diagram)
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Intraneural
transmission: within
on neuron
This is an
ELECTRICAL
process
Occurs as a result
of the exchange of
charged particles
called ions
Neural Impulse: Resting Potential
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When more negative ions are inside the neuron than outside
Neuron is not transmitting information
Similar to a compressed spring
The neuron is POLARIZED – meaning it has a charge (-)
System WANTS to reach equilibrium and balance charges, but
selectively permeable membrane is closed when in this state known
as resting potential
Neural Impulse: Action Potential
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Sudden, massive change in
charge in the neuron
Neuron reaches the
threshold of excitation when
neighboring neurons’
excitatory signals outnumber
inhibitory signals
Ions flow across cell
membrane down axon
(domino effect) facilitated by
myelin sheath
Na+ in, K+ out
Neuron fires and
DEPOLARIZES – no charge
Neural Impulse: All-or-None Law
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A neuron either fires or it
does not
When it does fire, it will
always produce an
impulse of the same
strength
Intensity of a stimulus is
coded by the frequency
of action potentials or
the number of neurons
that fire
Neural Impulse: Refractory
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Absolute refractory period
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Relative refractory period
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Period immediately after an action
potential when another action
potential cannot occur
Period following absolute
refractory period when a neuron
will only respond to a stronger than
normal impulse
During the refractory period, the
neuron is trying to get back to
resting potential by pumping out
K+ ions!
Dude…I’m in
refractory. No
action potential
here…
Hmpf
.
So…?
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Impulse has traveled down the length of the
axon
Signal end up at terminal buttons, very end
points of the axon terminals
Then what?
Signal must get to other neurons, but how?
The Synapse (diagram)
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The synapse
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Composed of the terminal button of one neuron,
the synaptic space, and the dendrites or cell body
of the receiving neuron
Synaptic space (synaptic cleft)
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Tiny gap between neurons
Messages must travel across the space to get
from one neuron to the next
Transmission Between Neurons
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Interneural: between
neurons
a CHEMICAL process
Synaptic vesicles
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Neurotransmitters
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Sacs in terminal button that
release chemicals into
synaptic space
Chemicals released by
synaptic vesicles
Receptor sites
Location on receptor neuron
for specific neurotransmitter
– Lock and key
 Reuptake
Postsynaptic
– “Recycling”
Neuron
neurotransmitters
–
Presynaptic
Neuron
Putting it together…
Neurotransmitters and Behavior (diagram)
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Neurotransmitters
regulate many
aspects of
behavior
An imbalance of
neurotransmitters
may cause
maladaptive
behavior
Neurotransmitters
may be inhibitory,
excitatory or both
Drugs and Neurotransmitters
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Drugs’ impact on the body
has helped scientists
discover neurotransmitters,
neuropeptides (e.g. amino
acids such as endorphins)
and neuromodulators that
can increase or decrease the
activity of certain
neurotransmitters
How do drugs work?
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Agonists mimic or prevent
reuptake (1, 3)
Antagonists block
neurotransmission (2)
Psychopharmacology
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Botulism
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Blocks release of ACh at
the neuromuscular junction,
causing paralysis
“Botox” is botulism toxin
used to prevent facial
muscles from making
wrinkles
Curare – found in vines in S.
America; used as poison
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Can stun or kill prey quickly
Blocks ACh receptors
causing paralysis
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Antipsychotic medications
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Caffeine
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Block dopamine receptors
Reduces schizophrenic
hallucinations
Increases the release of
excitatory neurotransmitters by
blocking the inhibitory
neurotransmitter adenosine
Cocaine
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Prevents reuptake of dopamine
Leads to heightened arousal of
entire nervous system
The Nervous System (diagram)
The Autonomic Nervous System (diagram)
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Fight-or-flight
response
Sympathetic: Arouses
Parasympathetic:
Calms
Central Nervous System
Brain
Spinal Cord
Central Nervous System (CNS)
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Brain
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Enables all functioning
Billions of neurons and their connections
These neurons work together in neural networks to facilitate
efficient output.
As we learn, these networks strengthen
Spinal Cord
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Connects brain to PNS
Handles reflexes
I rule.
The Endocrine System (diagram)
I hate being
naked in
front of all
these
students…
Tell
me
about
it!
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Helps coordinate and
integrate complex
psychological reactions
Endocrine glands secrete
hormones into the
bloodstream
Hormones serve to organize
the nervous system and body
Hormones also activate
behavior, such as sexual
behavior, hunger and
aggression
Dunno.
Got
diabeeetus?
diabeetusfetus
Endocrine Glands (diagram)
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Thyroid gland
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Regulates blood-sugar
levels
Secretes insulin
Diabetes?
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Referred to as the
“master gland”
regulates many other
glands
Adrenal glands
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Sleep-wake cycle
Secretes melatonin
Pancreas
Pituitary gland
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Pineal gland
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Secretes hormones
(primarily thyroxin) that
control metabolism
Hypothyroidism and
Hyperthyroidism
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Reaction to stress
Secretes adrenaline
(epinephrine)
Gonads
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Ovaries and testes
secrete estrogens and
androgens
The Brain
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Without our brains,
we would really be
nothing!
“The mind is what
the brain does”
Studying the Brain
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Studying the brain
through lesions or
damaged areas
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“Ta” and Phineas Gage
Experiments in rats –
hypothalamus lesions
Monitoring Electrical
Activity: the EEG
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Electroencephalograms
provide information about
cortical activity
Record electrical activity of
neurons on surface of
brain (neural firing)
A functional technique
Studying the Brain:
Structural Neuroimaging Techniques
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CT Scan (Computerized
tomography)
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Computer-assisted x-ray of
brain
Used to create overall images
of brain
MRI (Magnetic Resonance
Imaging)
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Produces detailed pictures of
soft tissue in brain
Can focus on specific regions
when CT cannot produce
clear images
CT scan
(top) and
MRI
(bottom)
showing a
tumor.
Studying the Brain:
Functional Neuroimaging Techniques
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PET (positron emission
tomography)
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Image created by the rate at
which radioactive glucose is
metabolized
Which areas of the brain are
active during a particular activity
fMRI (functional MRI)
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Combines structural and
functional techniques
Multiple images of brain created
during a particular task
Records changes in blood flow
to indicate regions of greater
activity
Primitive Brain Structures
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Brainstem
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Thalamus
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Oldest part of brain
Contains medulla, controlling heartbeat,
blood pressure and breathing
Also contains pons, which helps regulate
sensory information and facial expressions
Contains Reticular Formation (RF) for
alertness/arousal, sleep/wakefulness
Pair of egg-shaped structures on top of
brainstem
Routes all incoming sensory information
except for smell to appropriate areas of brain
Cerebellum
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“little brain” at read of brainstem
Controls coordination, balance, and muscle
tone
These parts of the brain are
our “autopilot” so other
regions can deal with higherlevel “human” functions
The Limbic System
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Located in between the primitive parts of the brain
and the cerebral hemispheres
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Hippocampus processes new memories (case of H.M.)
Amygdala controls emotions such as aggression and fear –
in animals, the “attack” response (rat study)
Hypothalamus regulates hunger, thirst, body temperature
and sex drive – also controls pituitary gland
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Rat study – self-stimulation of “pleasure centers”
Human implications? Mild pleasure, addiction tendencies?
Primarily, the limbic system processes drives, smell
and various emotional responses
The Cortex
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Part of the cerebrum, the
two large hemispheres
comprising 85% of brain
weight
Wrinkled outer layer
Why so convoluted?
Higher level functions
Designation of cortical
space and “higher level”
animals?
Most highly evolved part
of the human brain
Cortex Breakdown…
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Each hemisphere is
divided into 4 lobes
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Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe
The lobes are
separated by deep
convolutions known
as fissures
Homunculous!
Cortex Breakdown…
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Occipital Lobes
Parietal Lobes
Visual cortex
Damage?
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Temporal Lobes
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Auditory cortex
Auditory hallucinations?
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Primary sensory or
somatosensory cortex
Allocation of space?
Frontal Lobes
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Most evolved
Motor cortex, which
allows us to move
Allocation of space?
Motor and Sensory Cortex Revealed!
The Cortex: Association Areas
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We only use 10% of our brains?
Undifferentiated cortex
Association areas
Phineas Gage:
A Case Study in Frontal Lobe Association Area Damage
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In 1848, railroad
foreman Phineas
Gage – accident!
No longer
“himself”
Emotions, the
frontal cortex,
and the
unchecked limbic
system
The skull of Phineas and rogue tamping iron,
displayed proudly at Harvard University’s
medical school! For real!
Neuroplasticity
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Brain’s to change and
reorganize as a result of
experience
Mark Rosenzweig’s (19222009) Rat Studies (1950s60s)
Implications for humans?
Shafted
again.
Hey guys! Check out
our phat crib!
Party!
Neuroplasticity in Rats
Neurogenesis?
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Recent evidence has
suggested that human
brains may be able to
generate new brain cells,
known as Neurogenesis
Stem cell research?
The Two Hemispheres
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Two halves are NOT identical
Most have a dominant hemisphere – usually
the left, which controls the right side of the
body
Both sides serve important functions, revealed
by studying split-brain patients
Split-Brain
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Epilepsy, seizures and the
corpus callosum
Reduction in epileptic seizures
Different abilities in each
hemisphere
The story of “Vicki”
Michael Gazzaniga
Some Hemispheric Strengths
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Left Hemisphere
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Language in most
people: The cases
of Ta of Charles
Landry
Logic
Right side of body
Right Hemisphere
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Perception
Sense of self
Inferences
Hemispheric Dominance: Handedness
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90% of humans are right-handed
The 10% of left-handers show less predictable
patterns of hemispheric dominance
Causes?
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Genetics?
Fetal testosterone levels?
Learned?
Handedness and sexual orientation?
A closer look: a curse or an advantage?
Behavior Genetics:
What’s the Point?
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Behavior
Genetics seeks to
understand the
relative influence
of our heredity and
our experiences
Nature vs.
Nurture? It’s both –
but how much of
each?
Behavior Genetics:
Genetics Review
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Heredity examines the transmission of
trait from one generation to next
Chromosomes
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Deoxyribonucleic acid (DNA)
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Organic molecule arranged in a doublehelix
Contains the “code of life”
Genes
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Pairs of thread like bodies that contain
genes
Average human cell has 23 pairs
Sex cells?
Basic units of inheritance
Segment of DNA
Genome
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“map” for an organism’s genetic complete
make-up
Human Genome Project
Behavioral Genetics:
Studying Nature vs. Nurture
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Animal Studies
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Strain Studies
Selection Studies
Human Studies
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Identical Twins
Fraternal Twins
Separated Twins
Adoption Studies
Family studies
Behavioral Genetics:
Temperament and Heritability
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Temperament refers to emotional
reactivity and seems to be set very
early in life
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Thomas and Chess (easy, difficult,
slow-to-warm-up)
Kagan’s “shy child”
Indicates this aspect of behavior is
genetically manipulated
Environment can enhance or
diminish this genetic predisposition
Behavior Genetics: Heritability
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Heritability: the extent to which differences
among organisms are caused by genes
Does NOT refer to which percentage of a
trait is determined by genetics in a given
individual!
The more similar and controlled the
environment of the organisms is, the more
we can attribute differences to genes, and
the higher the heritability!
So…Nature vs. Nurture…?
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Genes and environment interact like “two hands
clapping…”
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Environment can trigger genetic “switches”
Our genes can provoke us to seek particular environments
e.g. Eating Disorders
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Genetic predisposition (some are more susceptible than others)
Cultural regulation (Western culture)
Molecular Genetics
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Studies how particular genes influence behavior
e.g. Is there a gene that determines obesity? Sexual
orientation?
Promise and peril of molecular genetics?
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Genetic engineering
Eugenics
Evolutionary Psychology
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Whereas behavior geneticists seek to explain
our behavioral differences in terms of our
genes, evolutionary psychologists focus on
our similarities, as dictated by natural
selection.
Richard Dawkins The Selfish Gene (1976)
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Varied organisms in a population compete to
survive
Certain biological and behavioral variations
facilitate survival
Surviving organisms may reproduce and pass
on their genes
This leads to overall changing characteristics in
a population
Evolutionary Psychology:
Natural Selection, Adaptation and Evolutionary Success
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Selection – providing a reproductive advantage, either naturally
or artificially (e.g. tame foxes), based on a trait/set of traits
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Variation can result from mutations (errors in genetic replication
right after conception)
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These traits will endure over time
Population will change as a result
Some of these “errors” provide an advantage and are selected for,
and therefore persist
The errors are adaptive – increasing our fitness, or our chances to
survive (and to reproduce)
Humans have so many shared characteristics – How?
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Differences that were not “fit” were not passed on
Those that increased survival were, as these organisms lived and
reproduced
Evolutionary Psychology
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Selection happens SLOWLY
and often our world changes
faster than the gene pool can
(e.g. fatty/sweet food
cravings)
Today, evolutionary
psychologists examine
persistent trends in human
behavior and seek to explain
them
Keep in mind, however, that
genetically driven tendencies
only partially govern human
behavior!
Evolutionary Psychology:
Explaining Human Sexuality and Mating
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Males of all sexualities
generally are more interested
in sex, regard sex as a
recreational activity and prefer
young, attractive mates
Females of all sexualities
generally see sex as an
outgrowth of relationships and
prefer mature, stable, and
affluent mates
Have these trends genetically
motivated?
Evolutionary Psychology:
Human Sexuality and Mating
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Women
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Men
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Perhaps males
should invest more in
child-rearing?
Quality over quantity
More invested in bearing/nurturing children
Seek men who either provide superb genes
(he-man strategy) or are good providers
(domestic-bliss strategy)
“fast” vs. “coy” females
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Quantity over quality
Increase reproductive success by
spreading their genes as widely as possible
Attraction to fertile females
Not physically bound to pregnancy
He-man strategy vs. opportunists
Philanderers vs. Stable males?
Evolutionary Psychology:
Criticism
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Do these arguments just provide
excuses for bad behavior?
Do humans have more of a
social and cultural responsibility
to make the world better?
What about environmental
influence?
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How does the environment
reinforce these trends?
How much of a role does
environment play in the
persistence of these roles?
Who benefits?
Parents and Peers
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Experience and Brain Development
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Parental Influence?
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Critical Periods
Rosenzweig revisited
Brains are shaped by our genes AND
experience
If abusive or neglectful, can have major impact
In non-extreme cases, parents probably deserve
less credit, or less blame!
Parents shape values, beliefs and habits, but not
as much as we may believe
Most important to provide unconditional love and
support
Peer Influence
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Peers teach us how to socialize and cooperate
Selection effect: seeking peers with similar
interests
Cultural Influences
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Culture
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distinctive values, beliefs,
language and characteristics of
a society
both tangible (food, clothing)
and intangible (values, beliefs).
Norms
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Rules that represent the typical
behaviors of a particular group
One example is expected
personal space, the distance
we like to keep ourselves from
other people
Individualism vs. Collectivism
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Individualist cultures place value of singular person over that
of the group
Collectivist cultures value the group over the individual
Which type of culture does the US have? Why?
Implications?
Gender Development
Aggression, Power, and Connectedness
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Aggression involves an intent to
harm, whether verbal or physical:
males admit to and exhibit more
than females.
Men are and are perceived as
more powerful and engage in
behaviors that exhibit and
perpetuate this power inequity.
Females place greater emphasis
on social connections, choosing
careers that involve social
interaction or require nurturing
roles
Males have more difficulty
admitting they are wrong
Why Are We Different?
Biological Explanations
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X and Y Chromosomes
Y triggers sex differentiation during
fetal development, causing greater
testosterone production in males
Female infants exposed to
elevated levels of testosterone
exhibit “male” behavioral
characteristics
Males with normal male hormones
but had their sex reassigned at
birth for various reasons often
embrace a male identity, despite
efforts to raise them as females
Why Are We Different?
Social Explanations
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Gender Roles – expected behaviors for males and
females
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Women as caregivers?
Men as breadwinners?
The Reality? Women now OUTNUMBER men in the
workplace in the US, yet in 87% of families with
children, are still the primary caregivers.
Variations across culture and time…
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Gender Identity – our sense of being male or female
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Gender typing – embracing a traditional masculine/feminine
role
Social Learning Theory and Gender Schemas
What do these roles and stereotypes provide for us?
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Sense of stability and simplification
Sense of confinement
Nature vs. Nurture?
Call the Whole Thing Off!
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Our genes and our experiences form us
Family, friends, and culture have an influence
over the genes that make us
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These structures are constantly in flux
We are adaptive creatures
The world changes, and we change with it