Psychology 1010 6.0 Section A Instructor: Professor Jennifer Steeves

Psychology 1010 6.0
Section A
Instructor: Professor Jennifer Steeves
e-mail: steeves@yorku.ca
telephone: 416-736-2100 X20452
Web: www.psych.yorku.ca/kopinska
Contact by email for appointment
Frequently asked questions
• Class is full, still try to enroll
• Can you post the slides because I can’t take
notes and listen… or I missed the last class…
• Am I responsible for the text, the lectures,
and the videos that you show in class?
• Don’t understand the assignment
• Where is the assignment posted?
Sample Question
factual:
A negative correlation means that:
a) high values of one variable are associated
with low values of the other.
b) high values of one variable are associated
with high values of the other.
c) low values of one variable are associated
with low values of the other.
d) there is no relationship between the two
variables.
e) none of the above
1
Sample Question
conceptual:
It is quite likely that the more classes students
miss, the lower their test grades tend to be.
This relationship illustrates a(n):
a) negative correlation
b) positive correlation
c) coefficient of correlation.
d) zero correlation.
e) a perfect positive correlation.
Sample question
applied:
Julie has found that the number of hours she sleeps each night
is related to the scores she receives on quizzes the next
day. As her sleep approaches eight hours, her quiz scores
improve; as her sleep drops to five hours, her quiz scores
show a similar decline. Julie realizes that:
a) there is a negative correlation between the number of hours
she sleeps and her quiz grades.
b) there is a positive correlation between the number of hours
she sleeps and her quiz grades.
c) her low quiz scores are caused by sleep deprivation the
night before a quiz.
d) she should sleep about ten hours a night to ensure 100
percent quiz grades.
e) high quiz scores are due to adequate sleep the previous
night.
2
The Brain: Source of Mind and Self
1.
The Nervous System
a.
b.
c.
2.
Neural Bases of Behaviour
a.
b.
c.
3.
Peripheral nervous system
Central nervous system
Hierarchical Brain: structures and functions
Neurons
Electrochemical process
Synaptic transmission
How we can study the brain
Show video P&B
Human Brain
~3 lbs
~2% of body weight
20% of body’s oxygen
consumption
CNS vs. PNS
Spinal
Cord
Brain
Nerves
Central Nervous System
• brain + spinal cord
Peripheral Nervous System
• nerves connecting CNS to
muscles and organs
3
Peripheral Nervous System
Peripheral Nervous System
Skeletal
(Somatic)
Autonomic
Sympathetic
Parasympathetic
Somatic System
• Sensory Neurons
– input from body to CNS
• Motor neurons
– output from CNS to
control muscle
movements
• Interneurons
– sensory-motor relay
within CNS
• Both voluntary and
reflex movements
• Spinal reflex arc
Reflexes
4
Peripheral Nervous System
Peripheral Nervous System
Skeletal
(Somatic)
Autonomic
Sympathetic
Parasympathetic
Autonomic Nervous System
The Sympathetic Nervous System
in Action
Sympathetic
• “fight or flight”
Parasympathetic
• “rest and digest”
5
Central Nervous System
Spinal
Cord
• brain
• spinal cord
Brain
Nerves
Spinal Cord
Spinal injuries
• input can’t get in
• output can’t get out
• different levels wired to
different body parts
– quadraplegic vs. paraplegic
Brain
6
Brain Stem and Thalamus
Brainstem and Midbrain
• postural reflexes
• vital reflexes (breathing
rate, heart rate)
• movements
• sleep & arousal
Thalamus
• relay or gateway or
“traffic officer”
• sensory messages
directed to higher
centres (except
olfaction)
7
Cerebellum
• “little brain”
• traditionally thought to help you “walk and chew gum at
the same time (balance and muscle coordination)
• scientists now realize it’s much more diverse and
sophisticated-- involved in higher cognitive tasks
Basal ganglia
• movement
• Parkinson’s disease affects BG circuits
– tremor
– rigidity
– problems initiating movements
Fig 5.7
Limbic system
• amygdala
– emotion
• hippocampus
– memory formation
• hypothalamus
–
–
–
–
–
–
regulate body functions
autonomic NS
hormones
drives
emotion
“4 Fs”
• pituitary gland
– receives messages from
hypothalamus
– Then sends hormones to
endocrine glands
8
Cerebral Cortex
• cortex = bark = outer surface of brain
Localization of Function
Phrenology
-bumps on the head
said to be related to
personality traits
Localization of Function
The Case of Phineas Gage
9
“Dr. Penfield, I smell toast!”
•
•
•
•
Wilder Penfield, Montreal Neurological Institute
Epilepsy surgery
Stimulate brain
can invoke movements, sensations, emotions, memories,
experiences
Each hemisphere is
divided into 4 lobes
Frontal
Parietal
Occipital
Temporal
Occipital Lobe
• Input from eyes via
optic nerve
• Contains primary visual
cortex
• Outputs to parietal and
temporal lobes
Occipital
Lobe
Primary
Visual
Cortex
10
Temporal Lobe
• Auditory cortex gets input
from the ears
• Visual Input from occipital
lobe
• Recognition and Memory
–
–
–
–
Auditory
Cortex
speech recognition
face recognition
word recognition
memory formation
Temporal
Lobe
• Outputs to limbic system,
basal ganglia, and
brainstem
Parietal Lobe
• Inputs from multiple
senses
Somatosensory
Cortex
– Input from touch to
somatosensory cortex
– Input from vision via
occipital lobe and
audition via temporal
lobe
Parietal
Lobe
• Output to frontal lobe
• Sensorimotor control
– hand-eye coordination
– eye movements
– attention
Frontal Lobe
• No direct sensory input
• Includes motor cortex
• Includes motor speech
area (Broca’s area)
• Important for planning
and sequencing ideas
Frontal Lobe
Broca’s
Area
Motor
Cortex
11
Brain has 2 Hemispheres
Sensory Information
sent to opposite
hemisphere
• Sensory data crosses over
in pathways leading to the
cortex
• Visual crossover
– left visual field to right hemisphere
– right field to left
• Other senses similar
The visual fields NOT the eyes cross over!!!
Contralateral Motor Control
• Movements controlled
Motor Cortex
by motor area
• Right hemisphere
controls left side of
body
• Left hemisphere
controls right side
• Motor nerves cross
sides in spinal cord
Somatosensory Cortex
12
Corpus Callosum
• Major ( but not only)
Medial surface of right hemisphere
pathway between sides
• Connects comparable
structures on each side
• Permits data received on
one side to be processed
in both hemispheres
• Aids motor coordination Corpus Callosum
of left and right side
Corpus Callosum
• What happens when the corpus
callosum is cut?
• Sensory inputs are still crossed
• Motor outputs are still crossed
• Hemispheres can’t exchange data
• Scientific American video
The ‘Split Brain’ studies
• Special apparatus
– picture input to just one side
of brain
– screen blocks objects on
table from view
Verbal
left
hemisphere
Nonverbal
right
hemisphere
13
Cell types in the brain
1) Glia
–
–
–
–
“glue”
support cells
constantly replacing themselves
~1 trillion glial (1,000,000,000,000) cells
2) Neurons
– information processing cells
– less able than other cells to replace themselves
– ~100 billion (100,000,000,000) neurons
14
Glia
support cells
– provide insulation
• increase speed of neurons
– provide nutrients
– keep toxic substances out
(blood-brain barrier)
– support neurons
– clean-up and repair
15
Information Flow
dendrites
– many dendrites per neuron
(“dendritic tree”)
– collect information from other
neurons
cell body
– one cell body per neuron
– normal cell regulation functions
– axon hillock sums inputs
axon
– one axon per neuron
– transmit signal
• can be over long distances (e.g.,
sensory neurons in toe)
– end feet (axon terminals)
communicate information to the
dendrites of other neurons
(synapses -- stay tuned)
Structure
indicates function
sensory neurons
cortex
– relay information
– not many dendrites
cerebellum
interneurons
– collect and integrate
information
motor neurons
– collect information
– long axons
Axons
Let’s take a closer look at what goes on in the
axons…
16
Let’s Zoom in on an Axon
Ion Distribution-- resting potential
Outside
Membrane
Inside
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
+
-
• Because of the A- inside and Na+ outside, there is a
voltage across the membrane
• Inside is 70 mV more negative than outside
• Resting voltage = -70 mV
So What?
• By storing up energy, you can use it later
• Analogy: water dam
• When nerve cell is stimulated → sudden
inflow of + charged Na+ across membrane
followed by outflow of K+
• → brief change in electrical voltage
• → The action potential
17
Membrane Potential (mV)
+50
Resting Potential
0
Resting membrane
potential
-70
Time 
Membrane Potential (mV)
+50
Hyperpolarization
0
-70
Time 
Membrane Potential (mV)
+50
Depolarization
0
-70
Time 
18
The Action Potential
Membrane Potential (mV)
+50
Threshold of
excitation
Na+ enters
cell
Na+ channels close
K+ channels open
K+ leaves cell
0
Larger
depolarization
Hyperpolarization
-60
-70
Nothing
happens At threshold,
Small
Voltage-gated
depolarization
Na+ channels open
below threshold
Resting membrane
potential restored
The cell won’t produce another action
potential until the resting potential has
been restored.
This is called the cell’s refractory period.
An action potential either occurs or it
doesn’t ... and if it occurs, it occurs
at full amplitude.
This is called the All-or-none Law
19
How is a Neuron Like a Toilet?
• threshold
• all-or-none
• refractory period
Rapid Action Potentials
• An action potential takes less than 1/1000 second
• You can have many action potentials in a row
– sometimes we’ll call action potentials “spikes”
– sometimes we describe an AP as the neuron “firing”
Action Potential Propagates
= depolarization (+)
20
Action potentials on their own are quite
slow and metabolically expensive
What can make them go faster?
Go Faster!
1. Wider diameter axons
– the squid’s solution -- giant axons (1 mm diameter)
Yeah, that’s fine if you’re a squid and don’t have a lot of neurons!
2. Saltatory conduction
Saltatory Conduction
= depolarization (+)
21
Action Potential Propagates
~30 metres/sec
~120 metres/sec
How Does Saltatory Conduction Work?
• Glia wrap around axon
• This insulation is called
myelin
• Nodes of Ranvier
– Gaps between glia
• Saltatory conduction
– Action potential jumps
between nodes
Myelin
• Myelin is mostly fat
• Fat is white
• White matter contains myelinated axons
gray matter
• dendrites, cell bodies, end feet
white matter
• axons
22
Myelinization
• not all neurons are covered in myelin at birth
• myelin develops in different regions at
different times
• simpler areas (sensory and motor) become
myelinated first
• myelination can continue until ~age 20 in
areas involved in abstract thinking
Yes, you CAN learn to think better, stronger and FASTER!
Multiple Sclerosis
• decay of myelin sheaths
• impaired sensation and
movement
• axons are exposed and
break down
• sclerosis = hardening
• may be an autoimmune
disorder
What makes an action potential begin?
Axon hillock
• “little hill” at the junction of
the cell body and the
beginning of the axon
• gathers information from
dendrites
• sort of like a “vote counter”
23
Synapses
= the connection between the axon of one
neuron and (usually) the dendrite of another
presynaptic
membrane
synaptic cleft
postsynaptic
membrane
Postsynaptic Potentials
• Postsynaptic
– on the dendrites (or sometimes the cell body) of the
receiving neuron
• Potential
– voltage difference
• Excitatory post-synaptic potentials (EPSPs)
– “yes” votes
• Inhibitory post-synaptic potentials (IPSPs)
– “no” votes
24
What happens when the action
potential reaches the end?
Synapses
presynaptic
membrane
synaptic cleft
postsynaptic
membrane
neurotransmitter
molecules
synaptic
vesicles
Receptors: “Lock and Key”
25
Synaptic
Transmission
precursor 1
SYNTHESIS
breakdown
product
transmitter
DEGRADATION
STORAGE
INACTIVATION
breakdown
product
2
7
5
REUPTAKE
6
RELEASE
4
3
RECEPTOR
BINDING
PSPs
Receptor binding
• opens ion
channels
Drug Actions
• Drugs can act at any stage of synaptic
transmission
• Agonists
– drugs that increase the effectiveness of synaptic
transmission
• Antagonists
– drugs that decrease the effectiveness of
Normal
Antagonist
Agonist
26
Acetylcholine
(ACh) Drugs
• neurotransmitter in the
PNS (neuromuscular
junction) and CNS that
involved in motor
control, learning and
memory, and sleep and
dreaming
Serotonin
• serotonin
– neurotransmitter involved
in emotions and dreaming
• depression
– common disorder
• 5% of population
depressed at any one
time
• 30% depressed at some
point during lifetime
• higher incidence among
women than men
– seems to be due to
reduced serotonin
• selective serotonin
reuptake inhibitors (SSRIs)
– e.g., Prozac, Paxil, Zoloft,
– selective for serotonin
– reuptake inhibitors prevent
serotonin from being taken
back up so it remains in
the synaptic cleft longer
Brief Overview of Neurotransmitters
NEUROTRANSMITTER
FUNCTIONS
DISEASES
DRUGS
Acetylcholine
Motor control over muscles
Learning, memory, sleeping & dreaming
Alzheimer’s ()
Nicotine ()
many toxins (e.g., spider
venom )
Norepinephrine
Arousal and vigilance, eating behavior
Dopamine
Reward and motivation, Motor control over voluntary movement
Schizophrenia ()
Parkinson’s ()
L-dopa for Parkinson’s ()
Amphetamine ()
Cocaine ()
Antipsychotics ()
Serotonin
Emotional states and impulsiveness, dreaming
Depression (), mania (
)
Prozac and other SSRIs ()
Ecstasy ()
LSD ()
Psilocybin (mushroom) ()
GABA
Inhibition of action potentials; anxiety and intoxication
Glutamate
Enhances action potentials, learning and memory
Adenosine
relaxation (sympathetic parasympathetic return)
Endorphins
Pain reduction, reward
Amphetamine ()
Valium ()
Barbiturates (“downers”) ()
Alcohol ()
Caffeine ()
Heroin
Morphine
Jogging
Chocolate
Substance P
Pain perception
Chili peppers
Anandamide
Enhancing forgetting?
THC (marijuana)
Chocolate (a lot!)
27
What can you do with a neuron?
• Perform computations
• Make muscles twitch
• Make glands squirt
Neural Computing
1,000 to 10,000 synapses per neuron
~3 neurotransmitters/neuron (range ~2-5)
4 neurotransmitters x 3 states = 81 states
~100 billion (100,000,000,000) neurons
28
Single-Neuron Recording
• Stick a thin electrode into an animal’s brain (rat, cat,
monkey)
• record action potentials from a single neuron
• measure neuronal firing under a range of conditions
Example: Head direction neuron in limbic system
EEG (electroencephalography)
• Measure voltage differences with electrodes
placed on the scalp
• “Like holding a microphone over a stadium”
EEG (electroencephalography)
Waveforms vary with brain states
Epileptic seizure
29
Event-related Potentials (ERPs)
Neuropsychological Patients
• Determine the performance deficits of patients who
have lesions (brain damage) to a specific part of the
brain
• Examples
– Phineas Gage
– Broca’s aphasia
– split brain patients
MRI vs. fMRI
MRI studies brain anatomy.
Functional MRI (fMRI)
studies brain
function.
30
Brain Imaging: Anatomy
CAT
Photography
PET
MRI
Functional MRI
Big magnet
(typical magnet is 60,000X earth’s magnetic field)
+ radio waves
MRI vs. fMRI
good resolution
(1 mm)
MRI
fMRI
poorer resolution
(~3 mm but can be better)
one image
…
many images
(e.g., every 2 sec for 5 mins)
↑ neural activity
 ↑ blood oxygen  ↑ fMRI signal
31
PET and fMRI Activation
Transcranial Magnetic
Stimulation (TMS)
• Virtual, temporary lesions
• Wire coil on head-- magnetic pulse-- causes
neurons to fire
• Video clip
How can genetics and evolutionary
theory explain behavior?
• Evolutionary psychology:
– Field of psychology emphasizing evolutionary
mechanisms that may help explain human
commonalities in cognition, development, emotion,
social practices, etc…
• Behavioural genetics:
– Interdisciplinary field of study concerned with the
genetic bases of individual differences in
behaviour
32
Unlocking the Secrets of Genes
• Genes and how they operate
– Chromosomes
• rod-shaped structures within cells that carry genes
– Genes
• functional units of heredity which are composed of DNA and
specify the structure of proteins
– DNA
• transfers genetic characteristics by way of coded instructions
for the structure of proteins
– genome
How can genetics and evolutionary
theory explain behaviour?
A. Genetics of Alcoholism
B. Genetics of Intelligence
C. Evolutionary Psychology of Altruism
How can we examine genetic
factors in behaviour?
1) Twin studies
Identical Twins
• monozygotic (MZ): originate
from one zygote (fertilized
cell)
• 100% relatedness
Fraternal Twins
• dizygotic (DZ): originate
from two separate zygotes
• 50% relatedness (same as
any two siblings)
33
Logic of Twin Studies
• Both identical and fraternal twins share
the same environment (same age, same
parents)
• Only MZ twins share exactly the same
genes
• Concordance: both twins share the same
trait
• Discordance: one twin has a trait that the
other doesn’t
• When we observe a trait exhibiting high
concordance for MZ but not DZ twins, we
can conclude the trait is strongly affected
by genetics
Comparison of Concordance
Rates Between MZ & DZ Twins
TRAIT
MZ (%)
DZ (%)
Blood type
100
66
Eye color
99
28
Mental retardation
97
37
Measles
95
87
Idiopathic epilepsy
72
15
Schizophrenia
69
10
Diabetes
65
18
Identical allergy
59
5
Tuberculosis
57
23
A) Genetics of Alcoholism
Concordance rates for alcoholism
• 77% MZ vs. 54% DZ for males (significant)
• 39% MZ vs. 42% DZ for females (notsignificant)
Concordance rates for drinking patterns
(frequency and amount)
• greater for MZ than DZ
• less severe drinking patterns are less
heritable, and more severe drinking patterns
are more heritable
34
How can we study genetic factors
in behaviour?
2) Adoption Studies
• Examine whether adopted children bear a
greater resemblance to their biological
parents and siblings or their adoptive
parents and siblings
• Can suggest whether genes or environment
(nature vs. nurture, nativism vs. empiricism)
play a greater role
Adoption Studies of Alcoholism
• First-degree relatives of alcoholics are three
to four times more likely to have alcoholism
than first-degree relatives of non-alcoholics
– ~ 20-25% of sons and brothers of alcoholics
become alcoholic, and 5% of the daughters and
sisters
• But how can you tell if it’s genes or
environment?
• Sons of alcoholic biological parents were
more likely to become alcoholics than sons of
non-alcoholic biological parents, even when
they were reared by non-alcoholic adoptive
parents. Same is true for females
How can we study genetic factors
in behaviour?
3) Artificial Selection Studies
• Specific strains of animals (usually rats) are
bred for a particular trait
• Strength of that trait is measured over
successive generations
35
Artificial Selection Studies of
Alcoholism
• breed strain of rats for alcohol preference
– one strain voluntarily drinks alcohol, prefers
alcohol to other liquids, works hard to obtain
alcohol and develops a physical dependency
– other strain does not show these characteristics
• the chemical composition of specific brain
mechanisms in these two strains is different,
suggesting a biological susceptibility to
alcoholism
Summary
Many experimental approaches show a genetic
influence on alcoholism
• twin studies
• adoption studies
• artificial selection studies
Does this mean that if your father is an
alcoholic, you will necessarily be one too?
B) Genes and Individual differences
• Twin studies also show a role of genetics in
psychological traits such as intelligence
36
Genes and Group Differences
• Tomato plant experiment
The Environment and Intelligence
•
•
•
•
Poor prenatal care
Malnutrition
Exposure to toxins
Stressful family circumstances
Artificial Selection for Intelligence
Tyron (1942)
• “maze-bright”: mate male
and female rats who made
the fewest mistakes in mazerunning
• “maze-dull”: mate male and
female rates who made the
most mistakes in mazerunning
• difference cumulates over
successive generations
37
Conclusion
• Feature such as intelligence seem to be heritable
Evolution
Charles Darwin
1809-1882
Darwin provided biology with its great
unifying principle:
“The Theory of Natural Selection”
38
Evolution
Pre-Darwinian views
Doctrine of Progression
The world is full of as many diverse forms
as it can be.
Each species exists because of a special
creation by God. One species could not
be derived from another.
Each species is a pre-ordained type.
Variation is due to error, in some cases
pathology.
But how does one explain fossils and other
apparently extinct species?
World cataclysms -- like the Great Flood.
39
The continuity of existing forms -- from
inanimate to animate, from plants to animals
was part of the Grand Ascending Chain of
Progression.
The top of the Chain was Western European
Man.
An obvious ally in this view was the Christian
Church.
Evolutionists
The French naturalist, JeanBaptiste Lamarck (1744-1829),
introduced the idea of the
inheritance of acquired
characteristics.
-- environmental effects on organ development
-- use and disuse leads to change
-- changes in form through conscious will
-- movement toward perfection
Darwin advocated the idea of Natural Selection
Darwin’s father, Robert
Darwin, was a successful
country physician
In 1825 at age 16,
Darwin was sent off to
Edinburgh to study
medicine, but he hated
it.
40
Captain Robert Fitzroy
1805-1865
Darwin spent from 1831 to 1837 on the Beagle
visiting Cape Verde Islands, Brazil, Montevideo,
Tierra del Fuego, Buenos Aires, Valparaiso, Chile,
the Galapagos, Tahiti, New Zealand, and Tasmania.
Darwin was impressed with fossils in Patagonia.
He was also
impressed with the
diversity of life in the
Galapagos Islands.
...the different species
of giant tortoises on the
different islands of the
Galapagos.
Darwin was also struck by
the fact that there were 14
different species of finches,
each of which had a beak
shape and size that was
adapted to its particular
ecological niche.
He collected all kinds of specimens, which
Fitzroy described as “cargoes of apparent
rubbish.”
41
After Darwin returned to England, he
befriended Sir Charles Lyell, the geologist,
and in 1839 married his cousin, Emma
Wedgewood.
He became secretary of the Geological
Society and began to write a series of
impressive works in biology and geology.
He did not publish his developing ideas on
natural selection until 1859.
Alfred Russel Wallace
1823-1913
Darwin was prompted in part by a letter he
received from Alfred Russel Wallace in
1858 in which Wallace outlined a similar set
of ideas.
They published a short paper
together in 1858 and then Darwin,
urged by his colleagues, published
“The Origin of Species” in 1859.
All 1500 copies sold out on the first
day!
“Descended from the apes!
My dear, we hope it is not true.
But if it is, let us pray that it may
not become generally known.”
42
But what is the Theory of Natural Selection?
Three Inductions and two Deductions
Induction 1:
Organisms have an enormous
capacity to overproduce.
Induction 2:
Populations (with a few exceptions)
remain remarkably stable.
Deduction 1: There is a struggle for survival.
Induction 3:
Individuals differ in their
characteristics and many of these
differences are heritable.
Deduction 2: Those individuals who possess
adaptive characteristics will reproduce
more successfully than those who don’t
and will pass on these characteristics
to their offspring.
Deduction 2: Those individuals who possess
adaptive characteristics will reproduce
more successfully than those who don’t
and will pass on these characteristics
to their offspring.
This last process is what Darwin meant by
‘Natural Selection’.
Evolution can be seen as the accumulation
of the changes in the population due to
natural selection.
43
C) Evolutionary Theory
NeoDarwinian Theory (natural selection
coupled with modern genetics) provides a
wonderful framework for understanding the
ultimate causes of behaviour
Ultimate causes: “why” questions
Proximate causes: “how” questions
The Puzzle of Altruism
“Why be nice (especially when it costs you)?”
• Cooperative traits: good for both self and
neighbours
• Altruistic traits: good for neighbours, bad for
self
• Darwinian theory does NOT predict altruism
• Darwin himself was puzzled by altruism
Some ground-nesting birds,
such as the Killdeer, use a
“broken-wing display” to lead a
potential predator away from
the nest.
Killdeer
Charadrius vociferus
44
Ground squirrels, for
example, give alarm
calls when they spot a
predator. This will
happen even when
they don’t have
offspring.
Golden-mantled
ground squirrel
The other squirrels in the area then run for
their burrows and hide.
Moreover, the ground squirrels
who give alarm calls are often
stalked and eaten by predators
like owls and badgers.
Why would they put
themselves at risk?
What do they get out of
doing this?
Kin Selection Theory
“I would gladly lay down my life for two
brothers or eight cousins.”
-- J.B.S. Haldane, English biologist
They are helping to ensure that their young
survive -- and since they share 50% of their
genes in common with their offspring, this
means that they are projecting their own
genes into the next generation.
One can see how this behaviour would
be selected.
45
Generationn
Genes for broken-wing display
X
Generationn+1
XXX
XX
In other words, one can see how the
behaviour will increase an individual’s
fitness -- the success that the
individual has in increasing its genetic
representation in subsequent
generations.
But not all behaviour will increase
individual fitness.
The Selfish Gene
“A chicken is just an egg's
way of making more eggs.”
Key Concept: Evolution
acts on the gene rather
than the individual or the
species.
Controversial among
evolutionary biologists
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The idea of kin selection can help explain
some otherwise puzzling phenomena.
Consider the case of Belding’s
Ground Squirrel, for example.
Female Belding’s Ground
squirrels are three times
more likely to give alarm
calls than male Belding’s
Ground Squirrels.
Belding’s
Ground Squirrel
Why?
Kin selection helps explain why.
Females on average migrate 50 m from
the burrow in which they were born.
Males on average migrate 400 m.
Male
Female
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Thus, if a female gives an alarm call, she is
much more likely to be warning a relative
than a male would if he gives an alarm call.
Notice that kin selection does not require
that the individuals know that they are
warning their relatives.
Reciprocal Altruism
Is it possible for altruistic behaviour to
occur among unrelated individuals?
The answer is yes.
Natural selection could favor altruistic acts
between unrelated individuals if the
individual performing the act at a
reproductive cost to itself received
repayment at a later time from the individual
it helped.
In a sense, reciprocal altruism
is like Aesop’s fable about
Androcles and the Lion.
The idea is also captured in common
phrases such as “You scratch my back and
I’ll scratch yours!”
Reciprocal altruism is extremely common in
human beings. Although it is far less
common in other animals, it does occur.
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Male baboons will form alliances where one
baboon will engage an alpha male in a fight
while the other copulates with the alpha
male’s female consort. On a later occasion
they will reverse their roles.
There is a real risk for
the individual who
engages the alpha
male in a fight.
Clearly then, there must be some payback
later.
In other words, reciprocity must occur.
Reciprocal altruism will emerge more often
in species where there is:
• Individual recognition
• Long-lived individuals
• Stable communities
• Well-developed memory
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Kin selection and reciprocal altruism
can reinforce one another.
Thus, altruistic behaviour is likely to
be more common in small towns than
in large urban centres.
Where is human evolution going?
• What traits does the current environment
select for?
• Are we still subject to selection?
• Designer babies
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