PSYC 1000- Psychology 10 Edition in Modules Summary Notes
Wundt’s student, Edward Titchener aimed to discover the mind’s structure. He
engaged people in introspection, although it was unreliable. It waned along with
William James considered functions of our thoughts and feelings. He often asked
“why?” He assumed that thinking, like smelling. Was adaptive. James is a
In 1920, two behavioralists, Watson and Skinner dismissed introspection and
defined psychology as “the scientific study of observable behavior.”
Another force was Freudian psychology, which emphasized how our unconscious
thought process & emotional responses to childhood experiences affect our
In 1960 Carl Rogers and Abraham Maslow (both humanistic psychologists) found
the above too limiting. They drew attention to ways that current environmental
influences can nurture or limit growth potential and having our needs for love and
Today, we define psychology as: “The science of behavior and mental processes.”
Nature vs. Nurture: Plato assumed that we inherit character and intelligence, and
certain ideas are inborn. Aristotle countered that nothing in the mind does not come
from the external world through the senses.
In the 1600’s, John Locke argued that the mind is a blank slate on which experience
writes. Rene Descartes disagreed, believing that the same ideas are innate. He
gained support from Charles Darwin 2 centuries later.
Darwin explained diversity through the process of natural selection. Evolution has
become an important principle for 21 century psychology.
“Nature works on what nature endows.” Every psychological event is
simultaneously a biological event. Thus, depression can be both a brain and a
The tribe of psychology is united by a common quest: describing and explaining
behavior and the mind underlying it.
Biological psychologists: study the links between brain and mind.
Developmental psychologists: study the changing abilities from womb to tomb.
Cognitive psychologist: experiment with how we perceive, think, and solve problems.
Personality psychologists: investigate our persistent traits.
Social psychologists: explore how we view and affect each other. Basic Research: pure science that aims to increase the scientific knowledge base.
Applied Research: scientific study that aims to solve practical problems.
Counseling psychology: a branch of psychology that assists people with problems in
living (ex. School, work, marriage issues)
Clinical Psychology: Studies, assesses, and treats people with psychological
Positive psychology: the scientific study of human functioning.
Community Psychology: studies how people interact with their social environments,
and how institutions affect individuals and groups.
Three phenomena; hindsight bias, judgmental overconfidence, and our tendency to
perceive patterns in random events illustrate why we cannot solely rely on intuition
and common sense.
Hindsight Bias (I knew it all along!)
- This phenomenon makes the history of the world seem like a chain of
- Errors in our recollections and explanations show why we need
- Good ideas are like good inventions- once created, they seem obvious.
- We tend to think we know more than we actually do. We tend to be more
confident than correct.
Perceiving Order In Random Events
- We are prone to perceive patterns
- Random sequences often don’t look random (Falk et. Al 2009)
The points to remember… those 3 phenomena often lead us to overestimate our intuition.
But scientific evidence inquiry can help us sift reality from illusion.
Theory: an explanation using an integrated set of principles that organizes
observations and predicts behaviors or events.
Hypothesis: a testable prediction, often implied by a theory.
Operational definition: A statement of the procedures used to define research
Replication: Repeating the essence of a research study, usually with the different
participants in different situations to see whether the basic finding extends to other
participants and principles.
Case Study: An observation technique in which one person is studied in depth in the
hope of revealing universal principles.
Naturalistic Observation: Observing and recording behavior in naturally occurring
situations without trying to manipulate and control the situation. Does not explain
behavior- it merely describes it. Some naturalistic findings...
Humans laugh 30 times more in social situations than solitary situations.
Life is fastest paced in Japan and Europe and slower in economically less-
Surveys can have hindered results due to wording of the survey, and sampling bias.
Correlation Coefficient: A statistical index of the relationship between two things
(from -1 to +1). A correlation coefficient helps us to see the world more clearly by
revealing the extent to which things relate.
Correlations help us predict. But, association does not prove causation. Correlation
indicates the possibility of a case-effect relationship but does not prove such.
Experiment: a research method in which an investigator manipulates one or more
factors to observe the effects on some behavior or mental process.
Experimental group: The group that is exposed to the treatment: that is, to one
version of the independent variable.
Control group: The group that is not exposed to the treatment. Serves as a
comparison for evaluating the effect of the treatment. This group is often given a
Double-blind procedure: A procedure in which both the research participants and
the research staff are ignorant about whether the participants have received the
treatment or a placebo.
Placebo effect: Experimental results caused by expectations alone: any affect on
behavior caused by the administering of an inert substance or condition.
Independent variable: the experimental factor that is manipulated; the variable that
might produce an effect on an experiment.
Dependent variable: The outcome factor; the variable that may change in response
to manipulations of the independent variable.
Cofounding variable: a factor other than the independent variable that might
produce an affect on an experiment.
MODULE FOUR :
In the early 1800’s, Franz Gall proposed that phrenology (studying bumps on the
skull) could reveal a person’s mental abilities and character traits.
Phrenology focused attention on the localization of function- the idea that various
brain regions have particular functions:
Within the past century, researchers seeking to understand the biology of the mind
have discovered that:
The body is composed of cells.
Among these are nerve cells that conduct electricity and “talk” to one
another by sending chemical messages across a tiny gap that
Specific brain systems serve specific functions (though not the
functions Gall proposed)
We integrate information processed in these different brain systems
to construct our experience of sights and sounds, meanings and
memories, pain and passion. Our adaptive brain is wired by our experience.
We are each a system composed of subsystems that are in turn composed of smaller
subsystems. Thus, we are biopsychosocial systems
o Neurons: a nerve cell; the basic building block of the nervous system.
- Each neuron consists of a cell body and its branching fibers. The bushy
dendrite fibers receive information and conduct it toward the cell body.
- From there, the cell’s lengthy axon fiber passes the message through its
terminal branches to other neurons or to muscles or glands. (Dendrites
listen; axons speak).
- Unlike short dendrites, axons may be very long.
- Some axons are encased in a myelin sheath, a layer of fatty tissue that
insulates them and speeds their impulses. If the myelin sheath
degenerates, multiple sclerosis results.
- The gap between two neurons is called a synapse.
o Neuron Functioning:
- Neurons transmit messages when stimulated by signals from our senses
or when triggered by chemical signals from other neurons.
- In response, a neuron fires an impulse called an action potential.
- An action potential is a brief electrical charge that travels down its axon.
- A neural impulse can travel from 2 to 180 miles per hour.
o Neuron Chemical Explanations:
- Neurons generate electricity from chemical events.
- Ions (electrically charged atoms) are exchanged.
- The fluid outside an axon’s membrane has mostly positively charged
ions; a resting axon’s fluid interior has mostly negatively charged ions.
- This positive-outside/negative-inside state is called the resting
- The axon’s surface is very selective about what it allows through its
gates. The axon’s surface is selectively permeable.
o The Process:
- When a neuron fires, the first section of the axon opens its gates, and
positively charged sodium ions flood through the cell membrane.
- This depolarizes that axon section, causing another axon channel to
open, and then another, etc.
- During a resting pause (the refractory period) the neuron pumps the
positively charged sodium ions back outside. Then it can catch fire again.
- Most signals are excitatory (like pushing an neurons accelerator), but
some are inhibitory (like pushing on the break).
- If excitatory signals minus inhibitory signals exceed a minimum
intensity, or threshold, the combined signals trigger an action potential.
- Increasing the level of stimulation above the threshold will not increase
the neural impulse’s intensity. They neuron’s reaction is an all-or-
nothing response: the neuron will either fire or not.
- When an action potential reaches the knob-like terminals at an axon’s
end, it triggers the release of chemical messengers called
neurotransmitters. - Neurotransmitters cross the synaptic gap and bind to receptor sites on
the receiving neuron. Then, electrically charged atoms flow in, exciting
or inhibiting the receiving neurons readiness to fire. Then, in a process
called reuptake, the sending neuron reabsorbs the excess
How Do Drugs And Other Chemicals Alter Neurotransmission?
When flooded with opiate drugs such as heroin and morphine, the brain may stop
producing its own natural opiates.
When the drug is withdrawn, the brain may then be deprived of any form of opiate,
causing intense discomfort.
Drugs and other chemicals affect brain chemistry at synapses, often by either
exciting or inhibiting neurons’ firing.
Agonist molecules may be similar enough to a neurotransmitter to bind to its
receptor and mimic its effects. Some opiate drugs are agonists and produce a
temporary “high” by amplifying normal sensations of arousal or pleasure.
Antagonists also bind to receptors but their effect is to block a neurotransmitter’s
functioning- neurotransmitter can no longer bind to site. Ex. Botulin, causes
paralysis by blocking ACh release, botox.
The Nervous System
The nervous system is the body’s speedy, electrochemical communication network,
consisting of all the nerve cells of the peripheral and the central nervous systems.
The brain and the spinal cord form the central nervous system (CNS), the body’s
The peripheral nervous system is the sensory and motor neurons that connect the
central nervous system to the rest of the body. Responsible for gathering
information and transmitting CNS decisions to other body parts.
Nerves, electrical cables formed of bundles of axons, link the CNS with the body’s
sensory receptors, muscles, and glands.
Information travels through the nervous system through three types of neurons:
1. Sensory Neurons: carry messages from the body’s tissues and sensory
receptors inward to the brain and spinal cord for processing.
2. Motor Neurons: carry instructions from the CNS out to the body’s muscles.
3. Interneurons: neurons within the brain and spinal cord that communicate
internally and intervene between the sensory inputs and motor outputs.
The Peripheral Nervous System:
o Has two components: somatic and autonomic.
o Our somatic nervous system enables voluntary control of our skeletal muscles.
o Our autonomic nervous system (ANS) controls our glands and the muscles of our
internal organs, influencing such functions as glandular activity, heartbeat, and
digestion. Usually operates autonomously.
o Our ANS serves two important, basic functions. The sympathetic nervous system: arouses and expands energy. If something
alarms or challenges you, your sympathetic nervous system will accelerate
your heartbeat. Arouses the body.
When the stress subsides, your parasympathetic nervous system will
produce opposite effects, conserving energy, decreasing your heartbeat, etc.
Calms the body
The Central Nervous System:
The human body has 40 billion neurons, each containing roughly 10,000 other
neurons; we end up with some 400 trillion synapses.
The brain’s neurons cluster into groups called neural networks.
Neurons network with nearby neurons with which they can have short, fast
The other part of the CNS, the spinal cord is a two way information highway
connecting between the peripheral nervous system and the brain. Ascending neural
fibers send up sensory information and descending fibers send back motor-control
The neural pathways govern our reflexes (automatic responses to stimuli).
A simple spinal reflex pathway is composed of a single sensory neuron and a single
motor neuron. These often communicate through an interneuron.
Another such pathway enables the pain reflex when your finger touches a flame,
neural activity (excited by the heat) travels via sensory neurons to interneurons in
your spinal cord. These interneurons respond by activating motor neurons leading
to the muscles in your arm. Because the simple pain-reflex pathway runs through
the spinal cord and right back out, your hand jerks away from the candle’s flame
before your brain receives and responds to this information that causes you to feel
The Endocrine System:
The endocrine system is a set of glands that secrete hormones into the bloodstream.
Hormone: chemical messengers that are manufactured by the endocrine glands,
travel through the bloodstream, and affect other tissues.
Some hormones are chemically identical to neurotransmitters, making the
endocrine and the nervous system close relatives.
Both produce molecules that act on receptors elsewhere.
The nervous system acts extremely quickly (fraction of a second); the
endocrine system may take several seconds for the hormone to reach the
Endocrine messages tend to outlast the effects of neural messages (that may
explain why upset feelings may linger beyond our awareness of what upset
In a moment of danger, our autonomic nervous system orders the adrenal glands
at the top of the kidneys to release epinephrine and norepinephrine (also called
adrenaline and noradrenaline). These hormones increase heart rate, blood pressure,
and blood sugar, providing us with a surge of energy. When the emergency ends,
these feelings linger for a while.
The most influential endocrine gland is the pituitary gland.
This is located in the core of the brain where it is controlled by an adjacent
brain area, the hypothalamus This gland releases a growth hormone that stimulates physical development.
Another, oxytocin enables contractions associated with birthing, milk flow
during nursing, and orgasm. Also promotes pair bonding, group cohesion,
and social trust.
Pituitary secretions also influence the release of hormones by other
endocrine glands. In short, this gland is a master gland ( whose own master
is the hypothalamus).
Brain pituitary other glands hormones body and brain.
^ This feedback system reveals the intimate connection of the nervous system and
the endocrine system. The nervous system directs endocrine secretions, which then
affect the nervous system.
Ex. Under the brains influence, the pituitary triggers your sex glands to
release sex hormones. These in turn influence your brain and behavior. So
too, with stress.
Endorphins: natural, opiate-like neurotransmitters linked to pain control and to pleasure.
Biological Perspective: concerned with the links between biology and behavior. Includes
psychologists working in neuroscience, behavior genetics, and evolutionary psychology.
A century ago, scientists used early clinical observations to reveal some brain-mind
Damage to one side of the brain often caused numbness or paralysis on the body’s
opposite side, suggesting that the body’s right side is wired to the brain’s left side,
and vice versa.
Damage to the back of the brain disrupted vision, and to the left-front part of the
brain produced speech difficulties.
Now, scientists can selectively lesion (tissue destruction. A brain lesion is naturally
experimentally caused destruction of brain tissue) tiny clusters of brain cells,
leaving the surrounding tissue unharmed.
Today, neuroscientists can stimulate various parts of the brain and note the effects.
Depending on the stimulated brain part, people may giggle, hear voices, turn their
head, feel themselves falling, or have an out of body experience.
An electroencephalogram (EEG) is an amplified recording of the waves of electrical
activity that sweep across the brain’s surface. Electrodes placed on the scalp
measure these waves.
Positron Emission Tomography (PET) Scan: a visual display of brain activity that
detects where a radioactive form of glucose goes while the brain performs a given
Magnetic Resonance Imaging (MRI): A technique that uses magnetic fields and radio
waves to produce computer-generated images of soft tissue. MRI scans show brain
Ventricles: fluid-filled brain areas.
Functional MRI (fMRI): a technique for revealing blood flow and, therefore, brain
activity by comparing successive MRI scans. fMRI scans show brain function. The Older Brain Structure:
o The Brainstem:
- The oldest part and central core of the brain, beginning where the spinal
cord swells as it enters the skull; the brainstem is responsible for
automatic survival functions.
- The brainstem handles heartbeat and breathing.
- It begins where the spinal cord swells slightly after entering the skull.
- This slight swelling is the medulla.
- Just above the medulla sits the pons, which helps coordinate
- The brainstem is a crossover point, where most nerves to and from each
side of the brain connect with the body’s opposite side.
o The Thalamus:
- Sitting atop the brainstem is the thalamus.
- The thalamus is a pair of egg-shape structures that act as the brain’s
- Receives information from all the senses except smell and routes it to
the higher brain regions that deal with seeing, hearing, tasting, and
- Also receives some of the higher brain’s replies, which it then directs to
the medulla and the cerebellum.
- The brain’s sensory switchboard, located on top of the brainstem; it
directs messages to the sensory receiving areas in the cortex and
transmits replies to the cerebellum and medulla.
o The Reticular Formation:
- Located inside the brainstem, between your ears.
- A finger-shaped network of neurons that extends from the spinal cord
right up through the thalamus.
- As the spinal cord’s sensory input flows up to the thalamus, some of it
travels through the reticular formation, which filters incoming stimuli
and relays important information to other areas of the brain.
- In 1949, Giuseppe Moruzzi and Horace Magoun discovered that
electrically stimulating the reticular formation of a sleeping cat almost
instantly produced and awake, alert animal.
- When Magoun severed a cats reticular formation without damaging the
nearby sensory pathways, the effect was equally dramatic: the cat lapsed
into a permanent coma.
- The reticular formation enables arousal.
- A nerve network that travels through the brainstem and plays an
important role in controlling arousal.
o The Cerebellum:
- The “little brain” at the rear of the brain-stem; functions include
processing sensory input and coordinating movement output and
- It enables nonverbal learning and memory.
- Also helps us judge time, modulate our emotions, and discriminate
sounds and textures. And it coordinates voluntary movement.
- If you injured your cerebellum, you would have difficulty walking,
keeping your balance, or shaking hands. Note: all of these occur without any conscious effort.
The Limbic System
A neural system composed of the hippocampus, amygdala, and hypothalamus.
Located below the cerebral hemispheres; associated with emotions and drives.
The hippocampus processes conscious memories. People who lose their
hippocampus to surgery lose their ability to form new memories of facts and events.
o The Amygdala:
- Two-lima bean sized neural clusters in the limbic system; linked to
emotion (aggression and fear).
- When removed by a neurosurgeon, ill-tempered animals turned into
mellow creatures. (Kluver and Bucy)
- These and other experiments have confirmed the amygdala’s role in rage
and fear, including the perception of these emotions and the processing
of emotional memories.
o The Hypothalamus:
- A neural structure lying below (hypo) the thalamus; it directs several
maintenance activities (eating, drinking, body temperature), helps
govern the endocrine system via the pituitary gland, and is linked to
emotion and reward.
- Some neural clusters in the hypothalamus influence hunger; others
regulate thirst, body temperature, and sexual behavior.
- Together, they help maintain a steady internal state.
- As the hypothalamus monitors the state of your body, it tunes into your
blood chemistry and any incoming orders from other brain parts.
- Ex. Picking up signals that you’re thinking about sex, your hypothalamus
will secrete hormones. These hormones will in turn trigger the adjacent
‘master gland,’ your pituitary to influence your sex glands to release
their hormones. These will intensify the thoughts of sex in your cerebral
cortex. (Note interplay between nervous and endocrine system)
- Considered a reward center.
- Other limbic system reward centers, such as the nucleus accumbens
were discovered in many other species.
- Some researchers belie that addictive disorders such as alcohol
dependence, drug abuse, and binge-eating may stem from malfunctions
in natural brain systems for pleasure and well-being.
- People genetically predisposed to this reward deficiency syndrome may
crave whatever provides that missing pleasure or relieves negative
The Cerebral Cortex
Older brain networks sustain basic life functions and enable memory, emotions, and
basic drives. Newer neural networks within the cerebrum- (the hemispheres that
contribute 85 percent of the brain’s weight) – form specialized work teams that
enable our perceiving, thinking, and speaking. The cerebral hemispheres come as a pair.
Covering these hemispheres, like bark on a tree, is the cerebral cortex (a thin
surface layer of interconnected neural cells)
What distinctively makes us human mostly arises from the complex functions of our
Cerebral cortex: the intricate fabric of interconnected neural cells covering the
cerebral hemispheres; the body’s ultimate control and information-processing
The Structure of The Cortex
The cerebral cortex contains some 20 to 23 billion nerve cells and 300 trillion
Supporting these billions of nerve cells are nine times as many spidery glial cells.
Glial Cells: Cells in the nervous system that support, nourish and protect neurons;
they may also play a role in learning and thinking. They provide nutrients and
insulating myelin , guide neural connections, and mop up ions and
neurotransmitters. May play a role in learning and thinking.
In more complex animal brains, the proportion of glia to neurons increases. A post-
mortem analysis of Albert Einstein’s brain did not find more or larger-than-usual
neurons, but it did reveal a much greater concentration of glial cells than average.
Each hemisphere’s cortex is subdivided into four lobes, separated by prominent
fissures or folds.
Starting at the front of your brain and moving over the top, there are the frontal
lobes (behind your forehead), parietal lobes (at the top and to the rear), and the
occipital lobes (at the back of your head).
Frontal lobes: a portion of the cerebral cortex lying just behind the forehead;
involved in speaking and muscle movements and in making plans and
Parietal Lobes: portion of the cerebral cortex lying at the top of the head and
toward the rear; receives sensory input for touch and body position.
Occipital lobes: portion of the cerebral cortex lying at the back of the head;
includes areas that receive information from the visual fields.
Reversing direction and moving forward, just above your ears you find the
Temporal lobes: portion of the cerebral cortex lying roughly
above the ears; includes the auditory areas, each receiving
information primarily from the opposite ear.
Functions of the Cortex:
o Motor Functions:
- Mild electrical stimulation to parts of an animal’s cortex made parts of its
body move. (Fritsch and Hitzig).
- Stimulating parts of this region in the left or right hemisphere caused
movements of specific body parts on the opposite side of the body.
- They discovered what is now called the motor cortex.
- Motor Cortex: an area at the rear of the frontal lobes that controls
voluntary movements. - Body areas requiring precise control, such as the fingers and mouth,
require the greatest amount if cortical space.
o Sensory Functions:
- The sensory cortex is an area at the front of the parietal lobes that
registers and processes body touch and movement sensations.
- The more sensitive the body region, the larger the sensory cortex area
devoted to it.
o Association Areas:
- Areas of the cerebral cortex that are not involved in primary motor or
sensory functions; rather, they are involved in higher mental functions
such as learning, remembering, thinking, and speaking.
- Electronically probing an association area won’t trigger and observable
response. So, these functions cannot be neatly mapped.
- Association areas are not dormant. Rather, these areas interpret,
integrate, and act on sensory information and link it with stored
- Association areas are found in all four lobes.
- In the frontal lobes, they enable judgment, planning, and processing of
new memories. Frontal lobe damage can alter personality and remove a
- In parietal lobes, mathematical and spatial reasoning are enabled.
- Another association area, on the underside of the right temporal lobe,
enables us to recognize faces.
The Brain’s Plasticity
Plasticity: the brain’s ability to change, especially during childhood, by reorganizing
after damage or by building new pathways based on experience.
The brain has the ability to modify itself after damage.
Some of the effects of brain damage can be traced to two hard facts:
1. Severed neurons, unlike cut skin, usually do not regenerate. (If your spinal
cord were severed, you would probably be permanently paralyzed).
2. Some brain functions seem pre-assigned to specific areas.
Some neural tissue can reorganize in response to damage. Our brains are constantly
changing, building new pathways as it adjusts to little mishaps and new experiences.
Plasticity may also occur after serious damage, especially in young children.
Constraint-induced therapy aims to rewire brains and improve the dexterity of a
brain-damaged child or even an adult stroke victim.
Although the brain often attempts self-repair by reorganizing existing tissue, it
sometimes attempts to mend itself by producing new brain cells. This process is
known as neurogenesis. This has been found in adult mice, birds, monkeys, and
Our Divided Brain
Our brain’s look-alike left and right hemispheres serve differing functions. This
lateralization is apparent after brain damage.
Accidents, strokes, and tumors in the left hemisphere can impair reading, writing,
speaking, arithmetic reasoning, and understanding. Similar lesions in the right
hemisphere seldom have such dramatic effects. o Splitting the brain:
- In 1961, Vogel and Bogen speculated that major epileptic seizures were
caused by an amplification of abnormal brain activity bouncing back and
forth between the two cerebral hemispheres. They wondered if they
could put an end to this by severing the corpus callosum.
Corpus callosum: the large brand of neural fibers connecting the
two brain hemispheres and carrying messages between them
- The seizures all but disappeared. The patients with these split brains
where surprisingly normal, their personality and intellect hardly
Split brain: a condition resulting from surgery that isolates the
brain’s two hemispheres by cutting the fibers (mainly those of
the corpus callosum) connecting them.
- Information from the left half of your field of vision goes to your right
hemisphere, which usually controls speech.
- Data received by either hemisphere are quickly transmitted to the other
across the corpus callosum. In a person with a severed corpus callosum,
this information sharing does not take place.
o Right-Left Differences in the Intact Brain
- When a person performs a perceptual task, brain waves, blood flow and
glucose consumption reveal increased activity in the right hemisphere.
- When the person speaks or calculates, activity increases in the left
- To the brain, language is language, whether spoken or signed. Just as
hearing people usually use the left hemisphere to process speech, deaf
people use the left hemisphere to process sign language.
- Although the left hemisphere is adept at making quick, literal
interpretations of language, the right hemisphere:
Excels in making inferences
Helps us modulate our speech to make meaning clear.
Helps orchestrate our sense of self.
Consciousness: Our awareness of ourselves and our environment. This awareness
allows us to assemble information form many sources as we reflect on our past and
plan for our future.
Some states of consciousness occur spontaneously: daydreaming, drowsiness,
Some states are physiologically induced: hallucinations, orgasm, food or oxygen
Some are psychologically induced: sensory deprivation, hypnosis, and meditation.
Cognitive neuroscience: the interdisciplinary study of the brain activity linked with
our mental processes.
Perception, memory, thinking, language, and attitudes all operate on two levels- a
conscious, deliberate “high road” and an unconscious, automatic “low road.”
Dual processing: the principle that information is often simultaneously processed on
separate conscious and unconscious tracks. Blindsight: a condition in which a person can respond to a visual stimulus without
consciously experiencing it.
Selective attention: the focusing of conscious awareness on a particular stimulus.
“The cocktail party effect”: your ability to attend to only one voice among many.
Inattentional blindness: failing to see visible objects when our attention is directed
Change blindness: failing to notice changes in the environment.
Behavior genetics: the study of the relative power and limits of genetic and
environmental influences on behavior.
Chromosome: Threadlike structures made of DNA molecules that contain genes.
Deoxyribonucleic acid (DNA): A complex molecule containing the genetic
information that makes up the chromosomes.
Genes: the biochemical units of heredity that make up the chromosomes; segments
of DNHA capable of synthesizing a protein.
Genome: the complete instructions for making an organism, consisting of all the
genetic material in that organism’s chromosomes.
You have 20,000 to 25,000 genes.
Genes can either be active (expressed) or inactive. Environmental factors “turn on”
genes, like hot water enabling a tea bag to express its flavor.
When turned on, genes provide the code for creating protein molecules, our body’s
Human genome researchers have discovered the common sequence within human
DNA- this shared genetic profile makes us humans.
We share about 96% of our DNA sequence with chimpanzees.
Our genetic predispositions –our genetically influenced traits- help explain both our
shared human nature and our human diversity.
Twin and Adoption Studies
o Identical Vs. Fraternal Twins
- Identical twins develop from a single (monozygotic) fertilized egg that
splits in two, thus are genetically identical.
- Although identical twins have the same genes, they don’t always have
the same number of copies of these genes. (Explaining why one twin
might be more at risk for a certain illness).
- Most identical twins share a placenta during prenatal development, but
one of every 3 sets has 2 separate placentas. One placenta may have
better nourishment, contributing to differences.
- Develop from separate (dizygotic) fertilized eggs. They share a fetal
environment, but are genetically no more similar that ordinary brothers
and sisters. Shares genes can translate into shared experiences. A person whose identical twin
has Alzheimer’s disease has a 60 % risk of getting the disease; if the affected twin is
fraternal, the risk is 30%.
Identical twins are much more similar than fraternal twins.
McGue and Lykken noted that if you have a fraternal twin who has divorced, the
odds of your divorcing are 1.6 times greater than if you have a non-divorced twin. If
your identical twin is divorced, the odds are now 5.5 times greater.
Identical twins, more than fraternal twins, also report being treated alike.
In explaining individual differences, genes matter.
o Biological Versus Adoptive Relatives:
- The stunning finding from studies of hundreds of adoptive families is
that people who grow up together, whether biologically related or not,
do not much resemble one another in personality.
- In traits such as extraversion and agreeableness, adoptees are more
similar to their biological parents than to their caregiving adoptive
- The environment shared by a family’s children has virtually no
discernable impact on their personalities.
- Most adopted children thrive, especially when adopted as infants (child
neglect and abuse and even divorce are rareadoptive parents are
- Regardless of personality differences between parents and their
adoptees, most children benefit from adoption.
Temperament and Heredity
Temperament: a person’s characteristic emotional reactivity and intensity.
Heredity predisposes one quickly apparent aspect of personality- temperament, or
From their first weeks of life, some infants are reactive, intense, and fidgety. Others
are easygoing, quiet, and placid.
Difficult babies are more irritable, intense and unpredictable. Easy babies are
cheerful, relaxed, and predictable in sleeping and eating. Slow-to-warm-up infants
tend to resist or withdraw from new people and situations (Chess and Thomas).
Temperament differences typically persist. Consider:
The most emotionally reactive newborns tend to also be the most reactive
Exceptionally inhibited and fearful 2 year olds are still relatively shy as 8
year olds; about half will become introverted adolescents.
The most emotionally intense preschoolers tend to be relatively intense
The genetic effect appears in physiological differences. Anxious, inhibited infants
have high and variable heart rates and a reactive nervous system. One form of a
gene that regulate the neurotransmitter serotonin predisposes a fearful
temperament and, in combination with unsupportive caregiving, and inhibited child.
Molecular Genetics The subfield of biology that studies the molecular structure and function of genes.
Seeks to identify specific genes influencing behavior.
Given that genes are typically not solo players, a goal of molecular behavior genetics
is to find some of the many genes that together orchestrate traits such as body
weight, sexual orientation, and extraversion.
Prenatal screening poses ethical dilemmas. In China and India, testing for an
offspring’s sex has enabled selective abortions.
The proportion of variation among individuals that we can attribute to genes. The
heritability of a trait may vary, depending on the range of populations and
Using twin and adoption studies, behavior geneticists can mathematically estimate
the heritability of a trait.
If the heritability of intelligence is 50%, meaning the genetic influence explains 50%
of the observed variation among people.
We can never say what percentage of an individuals personality or intelligence is
inherited. Heritability refers to the extent to which differences among people are
attributable to genes.
Genes are self-regulating; rather than acting as blue prints that lead to the same
results no matter the context, genes react.
People with identical genes but differing experiences will have similar but not
Genes and experience are both important- they interact. Environments trigger gene
Our genetically influenced traits evoke significant responses in others.
Genes can either be active (expressed) or inactive.
A new field called epigenetics is studying the molecular mechanisms by which
environments trigger genetic expression.
Epigenetics: the study of influences on gene expression that occur without
Although genes have the potential to influence development, environmental triggers
can switch them on or off.
The study of the evolution of behavior and the mind, using principles of natural
Natural Selection: the principle that, among the range of inherited trait variations,
those contributing to increased reproduction and survival will most likely be passed
on to succeeding generations.
Mutation: a random error in gene replication that leads to a change.
An Evolutionary Explanation of Human Sexuality
Males are more likely than females to initiate sexual activity. This is the largest
gender difference in sexuality, but there are others. In surveys, gay men (like straight men) report more interest in uncommitted sex,
more responsiveness to visual sexual stimuli, and more concern with their partner’s
physical attractiveness than do lesbian women.
Gay male couples also report having more sex than lesbian couples.
Although men are roughly 2/3 of the gay population, they were only about 1/3 of
those electing legal partnership.
Gender: in psychology, the biologically and socially influenced characteristics by
which people define male and female.
Our genes dictate our overall brain architecture, but experience fills in the details,
developing neural connections and preparing our brain for thought and language
and other later experiences.
Rats put in an enriched environment developed a heavier and thicker brain cortex.
After 60 days in the enriched environment, the rat’s brains increased 7-10% and the
number of synapses increased by 20%
Shared environmental influences from the womb onward typically account for less
than 10% of children’s differences.
Children in childhood and adolescence seek to fit in with groups and are influenced
Preschoolers who disdain a certain food will often eat it if that food is put
at a table with a group of children who like it.
Children who hear English spoken with one accent at home and another in
the neighborhood and at school, will adopt the accent of their peers, not
Teens who start smoking typically have friends who model smoking,
suggest its pleasure, and offer cigarettes,
Parents are more important when it comes to education, discipline, responsibility,
orderliness, charitableness, and ways of interacting with authority figures. Peers are more
important for learning cooperation, for finding the road to popularity, for inventing styles of
interaction among people that same age. Youngsters may find their peers more interesting,
but will look to their parents when contemplating their own futures.
Culture: The enduring behaviors, ideas, attitudes, values, and traditions shared by a
group of people and transmitted from one generation to the next.
Human nature seemed designed for culture. We are social animals and culture
provides a good way of being social.
Capacity for culture is similar across the world.
Culture transmits the customs and beliefs that enable us to communicate, to
exchange money for things, to play, to eat, and to drive with agreed-upon rules and
without crashing into each other.
o Variation Across Cultures:
- Human nature manifests human diversity. We see our adaptability in