The Biology
of Behavior
Chapter 2
Searching for
the biology of
“self”
2
Is our identity in the
heart?
In the brain?
In the whole body?
Biological
Psychologi...
Overview: What We Have in Mind
 Building blocks of mind: Neurons and how they
communicate (neurotransmitters)
 Systems t...
Neural and Hormonal Systems
Neurons and Neuronal Communication:
The Structure of a Neuron
There are billions of neurons
(nerve cells) throughout the b...
Action potential:
a neural impulse that travels down an
axon like a wave
Just as “the wave” can flow to
the right in a sta...
The
neuron
receives
signals
from other
neurons;
some are
telling it to
fire and
some are
telling it
not to fire.
• When th...
The synapse is
also known as the
“synaptic
junction” or
“synaptic gap.”
The Synapse
The synapse is a
junction between the
...
Neurotransmitters
Neurotransmitters are
chemicals used to send
a signal across the
synaptic gap.
Reuptake:
Recycling Neurotransmitters [NTs]
Reuptake:
After the neurotransmitters
stimulate the receptors on
the receiving...
Seeing all the Steps Together
Neural Communication:
Some Neurotransmitters and Their Functions
Neurotransmitter Function Problems Caused by Imbalances
Roles of Different Neur...
Serotonin
pathways
Networks of neurons that
communicate with serotonin
help regulate mood.
Networks of neurons that
commun...
Divisions of the Nervous System
The Inner and Outer Parts of the
Nervous System
The Central
Nervous
System (CNS),
the brain and
spinal cord, is
the body’s...
Types of Neurons
Sensory
neurons carry
messages IN
from the body’s
tissues and
sensory
receptors to the
CNS for
processing...
The Peripheral Nervous System
The
Autonomic
Nervous
System:
The sympathetic
NS arouses
(fight-or-flight)
The
parasympathetic
NS calms
(rest and digest)
Neural Networks
These complex webs of interconnected neurons form with
experience.
Remember: “Neurons that fire together, ...
Interneurons in the Spine
Decisions made without the brain
Your spine’s interneurons
trigger your hand to pull
away from a...
The Endocrine System
The
endocrine
system:
a set of
glands that
produce
chemical
messengers
called
hormones.
The Body’s “Slow but Sure”
Endocrine Message System
 The endocrine system sends
molecules as messages, just like the
nerv...
Tools of Discovery
and Brain Structures
What We’ll See:
How we learn about
the brain:
 Scans and more
The primitive, life...
Monitoring activity in the brain
Tools to read electrical, metabolic, and magnetic
activity in the brain:
EEG:
electroence...
25
An EEG (electroencephalogram)
is a recording of the electrical
waves sweeping across the
brain’s surface.
An EEG is use...
The PET scan allows us to see what
part of the brain is active by
tracing where a radioactive form
of glucose goes while t...
27
MRI (magnetic resonance imaging)
makes images from signals produced by
brain tissue after magnets align the spin
of ato...
The Brain:
Less Complex Brain Structures
Our tour of the brain begins with parts of the human
brain found also in simpler ...
The Brainstem:
Pons and Medulla
The Base of the
Brainstem:
The Medulla
 The medulla controls the most basic functions
such as heartbeat and breathing.
 ...
The Thalamus
 The thalamus is the
“sensory switchboard” or
“router”: All sensory
messages, except smell, are
routed throu...
Reticular (“net-like”) Formation
 The reticular formation is a
nerve network in the
brainstem.
 It enables alertness
(ar...
The cerebellum
helps coordinate
voluntary
movement such as
playing a sport.
Cerebellum (“little brain”)
The cerebellum has...
 emotions such as fear and
aggression.
 basic drives such as hunger and
sex.
 the formation of episodic
memories.
The h...
The Amygdala:
Enabling two different responses to threat
 Electrical stimulation
of one area of a cat’s
amygdala provokes...
 lies below (“hypo”) the thalamus.
 regulates body temperature and
ensures adequate food and water
intake (homeostasis),...
Review of Brain Structures
Higher Brain, Split Brain
Topics for your cortex to process:
 Cerebral Cortex
Structure: The
Lobes
 The motor and
sensor...
The Cerebral Cortex:
300 billion synaptic
connections
The brain has
left and right
hemispheres
 The outer grey “bark” str...
40
The Lobes of the Cerebral Cortex:
Preview
Frontal Lobes
Parietal Lobes
Occipital Lobes
Temporal Lobes
involved in speak...
Input: Sensory
cortex (Left
hemisphere
section receives
input from the
body’s right side)
Output: Motor
cortex (Left
hemis...
Sensory Functions of the Cortex
 The sensory strip deals
with information from
touch stimuli.
 The occipital lobe deals
...
The Visual Cortex
This fMRI scan
shows
increased
activity in the
visual cortex
when a person
looks at a
photograph.
Association function of the cortex
More complex animals have more cortical space
devoted to integrating/associating inform...
Case study: Phineas Gage
In a work accident, a metal rod
shot up through Phineas Gage’s
skull, destroying his eye and part...
Whole-brain Association Activity
Whole-brain association
activity involves complex
activities which require
communication ...
This 6-year-old had a
hemispherectomy to end life-
threatening seizures; her
remaining hemisphere
compensated for the dama...
Brain Studies
Researchers have studied the
impact of this surgery on
patients’ functioning.
Split-
To end severe
whole-bra...
Separating the Hemispheres:
Factors to Keep in Mind
 Each hemisphere controls the opposite side of
the body AND is aware ...
Split visual field
Each hemisphere
perceives the half of the
view in front of you that
goes with the half of the
body that...
51
Divided Awareness in the Split Brain
Try to explain the following result:
The divided brain in action
 Talent: people
are able to
follow two
instructions and
draw two
different shapes
simultaneou...
Our Two
Hemispheres
Lateralization (“going to one side”)
The two hemispheres serve some different functions.
How do we kno...
• Thoughts
and logic
• Language:
words and
definitions
• Pieces and
details
• Feelings
and
intuition
• Language:
tone,
inf...
Behavior Genetics and Evolutionary
Psychology
Behavior Genetics:
Predicting Individual Differences
More ways of exploring the
origins of the biology of
behavior:
1. Und...
Genes are
parts of DNA
molecules,
which are
found in
chromosomes
in the nuclei of
cells.
DNA
(Deoxyribonucleic Acid)
GENES...
Chromosomes are made of DNA,
which are made of genes.
}
Chromosome:
threadlike structure
made largely of DNA
molecules
DNA...
Chromosomes and Inheritance
 The human genome includes 46
chromosomes in 23 sets
matched sets; each
chromosome has the sa...
The Human Genome:
20,000 to 25,000 Genes
 Human genomes are so nearly
identical that we can speak of
one universal human ...
How Genes Work
 Genes are not blueprints;
they are molecules.
 These molecules have
the ability to direct the
assembly o...
Or vary the genes in the
same environment?
Next step for behavior geneticists:
Controlling Variables
Can we design an
expe...
Twin and
Adoption Studies
To assess the
impact of nature
and nurture, how
do we examine
how genes make a
difference within...
Twin and
Adoption Studies
How do we find
out how the same
genes express
themselves in
different
environments?
We can study...
Critiques of Twin Studies
1. In the more recent years of the
Minnesota Twin Family Study, twins
have known about each othe...
Searching for Parenting Effects:
Biological vs. Adoptive Relatives
Studies have been performed with adopted children for
w...
Despite the strong impact of
genetics on personality,
parenting has an influence on:
 religious beliefs
 values
 manner...
 Gene-Environment
Interaction: genes turn
each other on and off in
response to
environmental
conditions
 Epigenetics: Th...
69
Some topics:
 Natural selection and
adaptation
 Evolutionary success may help
explain similarities
 An evolutionary ...
Begin with a
species’ genome,
which contains a
variety of
versions of genes
that shape traits.
Conditions make it
difficul...
71
 Dmitri Balyaev and
Lyudmila Trut spent
40 years selecting
the most gentle,
friendly, and tame
foxes from a fox
popula...
72
Example:
 Why does “stranger anxiety”
develop between the ages of 9
and 13 months?
Hint: in evolutionary/survival
term...
73
 Why do people so easily
acquire a phobia of
snakes, more easily than a
phobia of cars?
 An evolutionary
psychologist...
Critiquing Evolutionary Psychology
“You’re just
taking current
reality and
constructing a
way you could
have predicted
it....
Evolution: Theory
 Evolution is a scientific theory
(NOT a “guess” and not a
hypothesis, but something
more): a coherent ...
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APPEL PSY 150 403 Chapter 2 SLIDES

  1. 1. The Biology of Behavior Chapter 2
  2. 2. Searching for the biology of “self” 2 Is our identity in the heart? In the brain? In the whole body? Biological Psychologists explore the associations between body, mind, and behavior.
  3. 3. Overview: What We Have in Mind  Building blocks of mind: Neurons and how they communicate (neurotransmitters)  Systems that build the mind: Functions of Parts of the Nervous system  Supporting player: the slower-communicating Endocrine system (hormones)  Tools for examining the brain and its activities  More primitive and advanced brain structures
  4. 4. Neural and Hormonal Systems
  5. 5. Neurons and Neuronal Communication: The Structure of a Neuron There are billions of neurons (nerve cells) throughout the body.
  6. 6. Action potential: a neural impulse that travels down an axon like a wave Just as “the wave” can flow to the right in a stadium even though the people only move up and down, a wave moves down an axon although it is only made up of ion exchanges moving in and out.
  7. 7. The neuron receives signals from other neurons; some are telling it to fire and some are telling it not to fire. • When the threshold is reached, the action potential starts moving. • Like a gun, it either fires or it doesn’t; more stimulation does nothing. • This is known as the “all-or- none” response. The action potential travels down the axon from the cell body to the terminal branches . The signal is transmitted to another cell. However, the message must find a way to cross a gap between cells. This gap is also called the synapse. How neurons communicate (with each other): When does the cell send the action potential? When it reaches a threshold. The threshold is reached when excitatory (“Fire!”) signals outweigh the inhibitory (“Don’t fire!”) signals by a certain amount.
  8. 8. The synapse is also known as the “synaptic junction” or “synaptic gap.” The Synapse The synapse is a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron.
  9. 9. Neurotransmitters Neurotransmitters are chemicals used to send a signal across the synaptic gap.
  10. 10. Reuptake: Recycling Neurotransmitters [NTs] Reuptake: After the neurotransmitters stimulate the receptors on the receiving neuron, the chemicals are taken back up into the sending neuron to be used again.
  11. 11. Seeing all the Steps Together Neural Communication:
  12. 12. Some Neurotransmitters and Their Functions Neurotransmitter Function Problems Caused by Imbalances Roles of Different Neurotransmitters Serotonin Affects mood, hunger, sleep, and arousal Undersupply linked to depression; some antidepressant drugs raise serotonin levels Dopamine Influences movement, learning, attention, and emotion Oversupply linked to schizophrenia; undersupply linked to tremors and decreased mobility in Parkinson’s disease and ADHD Acetylcholine (ACh) Enables muscle action, learning, and memory ACh-producing neurons deteriorate as Alzheimer’s disease progresses Norepinephrine Helps control alertness and arousal Undersupply can depress mood and cause ADHD-like attention problems GABA gamma- aminobutyric acid A major inhibitory neurotransmitter Undersupply linked to seizures, tremors, and insomnia Glutamate A major excitatory neurotransmitter; involved in memory Oversupply can overstimulate the brain, producing migraines or seizures; this is why some people avoid MSG (monosodium glutamate) in food
  13. 13. Serotonin pathways Networks of neurons that communicate with serotonin help regulate mood. Networks of neurons that communicate with dopamine are involved in focusing attention and controlling movement. Dopamine pathways
  14. 14. Divisions of the Nervous System
  15. 15. The Inner and Outer Parts of the Nervous System The Central Nervous System (CNS), the brain and spinal cord, is the body’s decisionmaker. The Peripheral Nervous System (CNS), gathers information from the body and sends CNS decisions out to the body.
  16. 16. Types of Neurons Sensory neurons carry messages IN from the body’s tissues and sensory receptors to the CNS for processing. Motor neurons carry instructions OUT from the CNS out to the body’s tissues. Interneurons (in the brain and spinal cord) process information between the sensory input and motor output.
  17. 17. The Peripheral Nervous System
  18. 18. The Autonomic Nervous System: The sympathetic NS arouses (fight-or-flight) The parasympathetic NS calms (rest and digest)
  19. 19. Neural Networks These complex webs of interconnected neurons form with experience. Remember: “Neurons that fire together, wire together.”
  20. 20. Interneurons in the Spine Decisions made without the brain Your spine’s interneurons trigger your hand to pull away from a fire before you can say OUCH! This is an example of a reflex action. The brain finds out about the reflex after it happens.
  21. 21. The Endocrine System The endocrine system: a set of glands that produce chemical messengers called hormones.
  22. 22. The Body’s “Slow but Sure” Endocrine Message System  The endocrine system sends molecules as messages, just like the nervous system, but it sends them through the bloodstream instead of across synapses.  These molecules, called hormones, are produced in various glands around the body.  The messages go to the brain and other tissues. Pituitary gland  The pituitary gland is the “master gland” of the endocrine system.  It is controlled through the nervous system by the nearby brain area--the hypothalamus.  The pituitary gland produces hormones that regulate other glands.
  23. 23. Tools of Discovery and Brain Structures What We’ll See: How we learn about the brain:  Scans and more The primitive, life- sustaining, inner parts of the brain:  The brainstem and limbic system Higher Brain structure that help us think and act:  The Cerebral Cortex
  24. 24. Monitoring activity in the brain Tools to read electrical, metabolic, and magnetic activity in the brain: EEG: electroencephalogram MRI: magnetic resonance imaging fMRI: functional MRI PET: positron emission tomography
  25. 25. 25 An EEG (electroencephalogram) is a recording of the electrical waves sweeping across the brain’s surface. An EEG is useful in studying seizures and sleep. EEG: electroencephalogram
  26. 26. The PET scan allows us to see what part of the brain is active by tracing where a radioactive form of glucose goes while the brain performs a given task. PET: positron emission tomography
  27. 27. 27 MRI (magnetic resonance imaging) makes images from signals produced by brain tissue after magnets align the spin of atoms. The arrows below show ventricular enlargement in a schizophrenic patient (right). MRI: magnetic resonance imaging Functional MRI reveals brain activity and function rather than structures. Functional MRI compares successive MRI images taken a split second apart, and shows changes in the level of oxygen in bloodflow in the brain. fMRI: functional MRI
  28. 28. The Brain: Less Complex Brain Structures Our tour of the brain begins with parts of the human brain found also in simpler animals; these parts generally deal with less complex functions: Brainstem (Pons and Medulla) Thalamus Reticular Formation Cerebellum Limbic System
  29. 29. The Brainstem: Pons and Medulla
  30. 30. The Base of the Brainstem: The Medulla  The medulla controls the most basic functions such as heartbeat and breathing.  Someone with total brain damage above the medulla could still breathe independently, but someone with damage in this area could not.
  31. 31. The Thalamus  The thalamus is the “sensory switchboard” or “router”: All sensory messages, except smell, are routed through the thalamus on the way to the cortex (outer brain).  These messages cross over from one side of the body to the opposite side of the brain. The crossover
  32. 32. Reticular (“net-like”) Formation  The reticular formation is a nerve network in the brainstem.  It enables alertness (arousal); stimulating this makes us wide awake.  It also filters incoming sensory information and relays it to other brain areas.
  33. 33. The cerebellum helps coordinate voluntary movement such as playing a sport. Cerebellum (“little brain”) The cerebellum has many other functions, including enabling nonverbal learning and memory.
  34. 34.  emotions such as fear and aggression.  basic drives such as hunger and sex.  the formation of episodic memories. The hippocampus (“seahorse”)  processes conscious, episodic memories.  works with the amygdala to form emotionally charged memories. The Amygdala (“almond”)  consists of two lima bean- sized neural clusters.  helps process emotions, especially fear and aggression. The Limbic (“Border”) System The limbic system coordinates:
  35. 35. The Amygdala: Enabling two different responses to threat  Electrical stimulation of one area of a cat’s amygdala provokes aggressive reactions.  If you stimulate a different part of the amygdala and put the cat in a cage with a mouse, the cat will cower in terror.
  36. 36.  lies below (“hypo”) the thalamus.  regulates body temperature and ensures adequate food and water intake (homeostasis), and is involved in sex drive.  directs the endocrine system via messages to the pituitary gland. The Hypothalamus: Thalamus Riddle: Why did the rat cross the grid? Why did the rat want to get to the other side? The Hypothalamus as a Reward Center Pushing the pedal that stimulated the electrode placed in the hypothalamus was much more rewarding than food pellets.
  37. 37. Review of Brain Structures
  38. 38. Higher Brain, Split Brain Topics for your cortex to process:  Cerebral Cortex Structure: The Lobes  The motor and sensory strips and association areas  Brain Plasticity  Functioning of he right and left hemispheres from cases of the divided and intact brains
  39. 39. The Cerebral Cortex: 300 billion synaptic connections The brain has left and right hemispheres  The outer grey “bark” structure that is wrinkled in order to create more surface area for 20+ billion neurons.  Organized into 4 lobes in each of two hemispheres.
  40. 40. 40 The Lobes of the Cerebral Cortex: Preview Frontal Lobes Parietal Lobes Occipital Lobes Temporal Lobes involved in speaking and muscle movements and in making plans and judgments include the sensory cortex include the visual areas; they receive visual information from the opposite visual field include the auditory processing areas
  41. 41. Input: Sensory cortex (Left hemisphere section receives input from the body’s right side) Output: Motor cortex (Left hemisphere section controls the body’s right side) Functions of the Brain: The Motor and Sensory Strips  Axons receiving motor signals FROM the cortex Axons sending sensory information TO the cortex
  42. 42. Sensory Functions of the Cortex  The sensory strip deals with information from touch stimuli.  The occipital lobe deals with visual information.  Auditory information is sent to the temporal lobe.
  43. 43. The Visual Cortex This fMRI scan shows increased activity in the visual cortex when a person looks at a photograph.
  44. 44. Association function of the cortex More complex animals have more cortical space devoted to integrating/associating information
  45. 45. Case study: Phineas Gage In a work accident, a metal rod shot up through Phineas Gage’s skull, destroying his eye and part of his frontal lobes. After healing, he was rude, odd, irritable, and unpredictable. Possible explanation for the change in personality: Damage to his frontal lobes hurt his ability to inhibit emotions and impulses.
  46. 46. Whole-brain Association Activity Whole-brain association activity involves complex activities which require communication among association areas across the brain such as:  memory  language  attention  meditation and spirituality  consciousness
  47. 47. This 6-year-old had a hemispherectomy to end life- threatening seizures; her remaining hemisphere compensated for the damage. Plasticity: The Brain is Adaptable If the brain is damaged, especially in the general association areas of the cortex:  the brain does not repair damaged neurons, BUT it can restore some functions  it can form new connections, reorganize, reassign brain areas to new functions.  Some neurogenesis, production of new brain cells, helps rebuild
  48. 48. Brain Studies Researchers have studied the impact of this surgery on patients’ functioning. Split- To end severe whole-brain seizures, some people have had surgery to cut the corpus callosum, a band of axons connecting the hemispheres.
  49. 49. Separating the Hemispheres: Factors to Keep in Mind  Each hemisphere controls the opposite side of the body AND is aware of the visual field on that opposite side.  Without the corpus callosum, the halves of the body and the halves of the visual field do not work together.  Only the left half of the brain has enough verbal ability to express its thoughts out loud.
  50. 50. Split visual field Each hemisphere perceives the half of the view in front of you that goes with the half of the body that is controlled by that hemisphere.
  51. 51. 51 Divided Awareness in the Split Brain Try to explain the following result:
  52. 52. The divided brain in action  Talent: people are able to follow two instructions and draw two different shapes simultaneously  Drawback: people can be frustrated that the right and left sides do different things
  53. 53. Our Two Hemispheres Lateralization (“going to one side”) The two hemispheres serve some different functions. How do we know about these differences?  Brain damage studies revealed many functions of the left hemisphere.  Brain scans and split brain studies show more about the functions of the two hemispheres, and how they coordinate with each other.
  54. 54. • Thoughts and logic • Language: words and definitions • Pieces and details • Feelings and intuition • Language: tone, inflection, context • Wholes, including the self The intact but lateralized brain Right-Left Hemisphere Differences Left Hemisphere Right Hemisphere
  55. 55. Behavior Genetics and Evolutionary Psychology
  56. 56. Behavior Genetics: Predicting Individual Differences More ways of exploring the origins of the biology of behavior: 1. Understanding genes 2. Twin and adoption studies 3. Gene/environment interactions 4. Evolutionary Psychology Behavior geneticists study how heredity and environment contribute to human differences. Let’s start by looking at GENES.
  57. 57. Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells. DNA (Deoxyribonucleic Acid) GENES: The Building Blocks of Heredity and Development Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells. GENES: The Building Blocks of Heredity and Development
  58. 58. Chromosomes are made of DNA, which are made of genes. } Chromosome: threadlike structure made largely of DNA molecules DNA: a spiraling, complex molecule containing genes
  59. 59. Chromosomes and Inheritance  The human genome includes 46 chromosomes in 23 sets matched sets; each chromosome has the same gene locations.  This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y.  A biological parent donates half his/her set of chromosomes to his/her offspring.  We received half a set of chromosomes from each biological parent.
  60. 60. The Human Genome: 20,000 to 25,000 Genes  Human genomes are so nearly identical that we can speak of one universal human genome.  Yet tiny genetic differences make a difference. If there is a:  .001 percent difference in genome, your DNA would not match the crime scene/you are not the baby’s father.  0.5 to 4 percent difference in genome, you may be a chimpanzee.  50 percent difference in genome, you may be a banana. The genome: an organism’s entire collection of genes
  61. 61. How Genes Work  Genes are not blueprints; they are molecules.  These molecules have the ability to direct the assembly of proteins that build the body.  This genetic protein assembly can be turned on and off by the environment, or by other genes.  Any trait we see is a result of the complex interactions of many genes and countless other molecules.
  62. 62. Or vary the genes in the same environment? Next step for behavior geneticists: Controlling Variables Can we design an experiment to keep genes constant and vary the environment and see what happens?
  63. 63. Twin and Adoption Studies To assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment?  study traits of siblings vs. identical twins  see if the siblings vary more than twins Fraternal and Identical Twins Fraternal “twins” from separate eggs are not any more genetically alike than other siblings. Identical twin: Same sex only Fraternal twin: Same or opposite sex
  64. 64. Twin and Adoption Studies How do we find out how the same genes express themselves in different environments? We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study). Identical vs. Fraternal Twins Studies of twins in adulthood show that identical twins are more alike than fraternal twins in:  personality traits such as extraversion (sociability) and neuroticism (emotional instability).  behaviors/outcomes such as the rate of divorce.  abilities such as overall Intelligence test scores.
  65. 65. Critiques of Twin Studies 1. In the more recent years of the Minnesota Twin Family Study, twins have known about each other and may influence each other to be more similar. 2. Coincidences happen; some randomly chosen pairs of people will have similar traits. 3. Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values. Studies of Identical Twins Raised Apart Similarities found in identical twins despite being raised in different homes:  personality, styles of thinking and relating  abilities/intelligence test scores  attitudes  interests, tastes  specific fears  brain waves, heart rate BUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins.
  66. 66. Searching for Parenting Effects: Biological vs. Adoptive Relatives Studies have been performed with adopted children for whom the biological relatives are known. Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives. Given the evidence of genetic impact on how a person turns out, does parenting/nurture make any difference? Does the home environment have any impact?
  67. 67. Despite the strong impact of genetics on personality, parenting has an influence on:  religious beliefs  values  manners  attitudes  politics  habits Parenting Does Matter
  68. 68.  Gene-Environment Interaction: genes turn each other on and off in response to environmental conditions  Epigenetics: The study of how this happens: The environment acts on the surface of genes to alter their activity How does the interaction of genes and environment work? Example in animals: shortened daylight triggers animals to change fur color or to hibernate Example in humans: obesity in adults can turn off weight regulation genes in offspring
  69. 69. 69 Some topics:  Natural selection and adaptation  Evolutionary success may help explain similarities  An evolutionary explanation of human sexuality Evolutionary Psychology: Understanding Human Nature Evolutionary psychology is the study of how evolutionary principles help explain the origin and function of the human mind, traits, and behaviors. We have been talking so far about human differences; we may now seek insight in the ways in which humans are alike.
  70. 70. Begin with a species’ genome, which contains a variety of versions of genes that shape traits. Conditions make it difficult for individuals with some traits (some versions of those genes) to survive long enough to reproduce. Other individuals thus have their traits and genes “selected” to spread in the population. Evolutionary Psychology: Natural Selection: How it Works
  71. 71. 71  Dmitri Balyaev and Lyudmila Trut spent 40 years selecting the most gentle, friendly, and tame foxes from a fox population, and having those reproduce.  As a result, they were able to shape avoidant and aggressive creatures into social ones, just as wolves were once shaped into dogs. Artificial Selection The Domesticated Silver Foxes
  72. 72. 72 Example:  Why does “stranger anxiety” develop between the ages of 9 and 13 months? Hint: in evolutionary/survival terms, humans are learning to walk at that time. Infants who used their new ability to walk by walking away from family and toward a lion might not have survived to reproduce as well as those who decided to stay with parents around the time they learned to walk. How might evolution have shaped the human species?
  73. 73. 73  Why do people so easily acquire a phobia of snakes, more easily than a phobia of cars?  An evolutionary psychologist would note that snakes are often poisonous… …so, those who more readily learned to fear them were more likely to survive and reproduce. Evolutionary Psychology’s Explanation of Biologically Driven Phobias
  74. 74. Critiquing Evolutionary Psychology “You’re just taking current reality and constructing a way you could have predicted it.” This is hindsight reasoning and unscientific. “You’re attributing too much to genes rather than the human ability to make choices about social behavior.” Response: yes, but there are predictions made about future behavior using this reasoning. Response: yes, but our evolutionary past does not prevent our ability to act differently; “is” does not equal “ought.”
  75. 75. Evolution: Theory  Evolution is a scientific theory (NOT a “guess” and not a hypothesis, but something more): a coherent set of principles that fits very well with the accumulated evidence.  Parts of the evolutionary story may conflict with other stories of origins and change over time.  Is there room for overlap and agreement? Possible areas of consensus, with or without evolution:  The human mind and body seems almost “designed,” by evolution or other forces, to have certain traits and abilities.  Nurture may shape us, but we seem to start out with some sort of human nature.

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