Transcript Chapter 5

Chapter 12
Evolutionary Psychopathology and
Darwinian Medicine
Division
• Evolutionary Psychopathology
– Study of mental illness within an evolutionary
context
• Darwinian Medicine
– Evolutionary theory applied to both psychiatric
and non-psychiatric health issues
Levels
• Traditional
– Proximate
– Etiology (cause) and pathogenesis (mechanism)
– “How” questions
• Evolutionary medicine
– Ultimate
– “Why” questions
Parasites and Hosts
• “Arms race”
• Red Queen theory
• Adaptation and counter adaptation
Symptoms
• Traditionally, all symptoms seen as
pathological (to be treated)
• Adaptation in parasite
– To propagate copies
• Adaptation in host
– To destroy/resist/expel parasite
– Defense mechanisms evolved for protection
– Such symptoms actually beneficial in long run
Bacterial Infection
• Single celled microbes
• Leukocyte endogenous mediator (LEM)
released by body when infected with bacteria
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–
–
–
Raises body temperature
Iron withdrawal from bloodstream (into liver)
Symptomatically --> fever and fatigue
Bacteria need iron to reproduce and are
susceptible to higher temperatures
• Treatment of fever and iron supplements
counter body’s evolved defenses
Cholera (Vibrio cholerae)
• Parasite induced symptoms
• Benefit spread of parasite
– Contaminated water
– Infection induces diarrhoea; dehydration can
kill host quickly
– But, passes more parasites back into water
system
– Spreads to more hosts
– Fast replicating microbe
Bubonic Plague (Yersinia pestis)
• Most often, person infected by
bite from flea, infected by biting a
rodent that was infected by a bite
from a flea
• Bacteria multiply in flea, blocking
its stomach, causing it to starve;
hungry flea voraciously bites host
trying to feed, expelling bacteria
in the processes
Source: en.wikipedia.org/wiki/
Bubonic_plague
• In mammals, bacteria reproduces in cells,
collecting in lymph nodes
• Eventually so many bacteria in lymph nodes that
they “spill” out into bloodstream
• Septicimic form: infect organs, cause bleeding in
and under skin
– Contact with broken skin can infect other hosts
• Pneumonic form: infects lungs
– Coughing transmits bacteria to other hosts on airborn
repiratory droplets
• 1347-1351: killed 1/3 to 1/2 of
European population
Source: www.insecta-inspecta.com/fleas/bdeath/Art_music.html
Viral Infections
• Submicroscopic strands of DNA or RNA
• “Assisted” self-replicating infectious agent
– Need another organism’s cells to reproduce
– Obligate parasites
• E.g., rabies, yellow fever, smallpox, West
Nile, herpes
Ebola
• Group of filoviruses
• Early symptoms: headache; joint,
muscle, abdominal pain;
weakness; nausea
• Later symptoms: diarrhea,
vomiting, internal and external
hemorrhages, coughing blood
• Transmitted via body fluid
contact
• 50-90% fatal
Source: en.wikipedia.org/wiki/Ebola
Parasite/Host Benefit Crossover
• Some symptoms benefit both parasite and
host
• E.g., coughing expels parasite from host,
but spreads it to other hosts
• Consider selfish gene theory here
Immune System
• Lymphocytes
– B-cells (from bone marrow) and T-cells (from
thymus)
• Antigens (foreign molecules) activate
immune system
– B-cells produce antibodies (proteins) that
circulate in blood and attach to antigens,
marking them for destruction by white blood
cell macrophages
– T-cells also attack antigen and help with
antibody production
Complexity
• Millions of different antigens
• Lock (antibody) and key (antigen) analogy
• Can’t store millions of of each antibody ready and
waiting, but can store a few of each type
• When specific antigen identified a lymphocyte,
that lymphocyte starts replicating rapidly to
combat infection
• With time, our immune systems have evolved (and
stored) the genes to make the various antibodies
MHC
• Major histocompatibility complex (MHC)
• Genes
– Code for disease detectors (antibodies) in the
immune system
• In humans
– Human leukocyte antigen (HLA)
In Mice
• Male mice secrete MHC in urine
• Female mouse meets males
– Smells urine
– Preference for mating with male with MHC
most different from her own
In Humans
• Don’t usually smell pee...
• Sweat
– MHC
• Saliva?
– Kissing?
Claus Wedekind
• 49 men
• Wear T-shirt 2 days; no spicy food, perfumes,
etc.
• 44 women smelled shirts
• Rated for sexiness, pleasantness, intensity
• Women prefer scents of men with maximally
different MHC
Women’s Sense of Smell
• Most sensitive during ovulation
– Conception
• Contraceptive pill
– Interferes with sense of smell
– In Wedekind’s study, no correlation between
preferences and MHC
HLAs
• A variety of HLAs
– A1, A2, B, DR
• Rate perfumes for self or other to wear
• Positive correlation between HLA-As and
perfume for self
– Preferences for self, but not for other
(advertising?)
MHCs and Like-Avoidance
• Variability in the population, in offspring
• Heterozygous condition may confer better
disease resistance
• “Hybrid vigour”
• Remember, parasite and host are constantly
“upgrading” with new adaptations to
combat each other’s defenses
Blood Groups
• A, B, AB, O
• Offer protection against various diseases
• Cholera
– AB most resistant (virtually immune)
– Then, A, B, and O least resistant
– So why doesn’t O vanish from population?
• Malaria
– Type O more resistant
– Also, maybe less likely to get some cancers
Hutterites of North Dakota
• Small communities
• Not much outbreeding
• Marriages of people with matched MHCs
– Fewer pregnancies
– More miscarriages
Psychiatric Problems
• Psychiatric disorders not (usually) due
to parasites
• Genes and/or environmental effects
• Why hasn’t evolution selected against
them?
Pleiotropy Argument
• Genes’ predispositions to psychiatric
disorders may also have inclusive
fitness benefits
• Genes can have multiple phenotypic effects
• Negative effects of a gene may be
maintained in gene pool if positive effects
outweigh them
Time Lag Argument
• Environmental differences from EEA;
still adapting to cope
• Environment can shift rapidly
• Humans can directly or indirectly speed
environmental change
• Selective pressures still “catching up”
Compromise Argument
• Design compromises, not genetic flaws
• Selective pressures act on inclusive
fitness
• Evolution doesn’t act to design optimal
systems
• Sufficient degree of differential
reproductive success is the requirement
Trait Variation Argument
• Normal distribution
curve for traits in
population
• Individuals’
characteristics due
to genetic and
environmental
effects
• Most individuals in
middle; very few on
the extremes
Anxiety
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Very basic and adaptive
Feeling of apprehension, nervousness
Xenophobia
Very, very ancestral
Mammals
• Eomaia (~125mya)
• Primate ancestor very like
modern tree shrew
• Small insectivores
• A meal for anything bigger
www.hoglezoo.org/animals/view.php?id=183
en.wikipedia.org/wiki/Eomaia
www.ryanphotographic.com/images/JPEGS/Tree%20shrew.jpg
Benefit of Anxiety
• Focuses attention
• Prepares species specific defense reactions
– Freeze, flight, fight
• “Smoke detector” model
– “Better to be safe than dead”
– Consequence of being anxious when not
necessary (e.g., false alarm) better than not
being anxious when you should
Evolved for Constant Anxiety?
• For short periods, not problematic
• Difficulties arise when constantly in this
state
– Physiological stress
– Costs in terms of lost time foraging, mating,
childrearing, etc.
Anxiety Disorders
• Time lag
– Haven’t adapted yet to limited threats in
Western society
– Alternatively, modern features can allow you to
stay in anxious state
• E.g., agoraphobia (instead of having to go out to
forage, just order delivery and stay in)
• Trait variation
– Problems with anxiety when at the extremes
(too little or too much)
Depression
• Affective disorders
– Mood disturbances and depression
• Reactive depression
– Normal response to specific life events
• Endogenous/clinical depression
– Severe, long-term, may not be related to
specific event
• Unipolar depression and bipolar disorder
• Three classes of evolutionary models
Ultimate Cause Models
• Adaptive trait
– Depression as response to adverse condition
– Provides motivation for some action
• Pleiotropy
– Genes increasing inclusive fitness (e.g.,
creativity, introspection) also predispose
individual to depression
• Trait variation
– Chance mixing of genes at conception; outliers
in population
Developmental Disruption Models
• Environmental developmental disruption
affects genetically normal individual
– E.g., toxins, neurological damage
• Adverse social effects
– E.g., abandonment, lack of social interaction
• Generally, phenotypic interpretations
Ultimate-Proximate Interactions
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Social competition hypothesis (Price, 1967)
Decline in social status
Interpersonal conflict resulting in loss
Fall in status/personal loss triggers
depression
• Depression appears less threatening, ends
conflict (communication)
• Depression allows individual to accept defeat
Serotonin
• Vervet monkeys
• Alpha has highest serotonin levels
• If alpha loses status, behaviourally appears
depressed, and serotonin levels drop to low
• Give Prozac (selective serotonin reuptake
inhibitor)
– Fallen alpha stops depressed behaviour
– Non-alpha male on Prozac becomes alpha
Possible Modern Contributors
• Mass communication
• In EEA all comparison was to others in
relatively small social group
• With TV and movies we compare to the
“best” from a much larger population
• Physical comparison to stars, models leads
to negative body image; taken to extreme,
depression
• Loss of family and community structure
• Quite different from EEA
• Kinship support networks (indirect fitness
benefits)
• Small social groups promote reciprocal
altruism (“support networks”)
• Postpartum depression
– Possibly a non-linguistic way to communicate
stress and the need for assistance immediately
after childbirth
– If no support immediately provided, depression
ramps up to make communication more obvious
Schizophrenia
• About 1/100 people
• “Split mind”
– Cognitive, emotional and motivation processes
• Hallucinations, delusions, affective
disorders, bizarre beliefs
• Difficulty maintaining social relationships
• Chronic and acute forms
Genetics
• Long recognized to run in families
• As r-value with schizophrenic increases, so
does the probability of having the disorder
• But, not strictly hereditary
– Siblings, 7.3% (r = 0.5)
– Dizygotic twins, 12.08 (r = 0.5)
– Monozygotic twins, 44.3 (r = 1.0)
Diathesis-Stress Model
• Doesn’t follow strict Mendellian rules
• Individual may have genes for
schizophrenia, but only phenotypically
express them after particularly stressful life
event
• Genes create predisposition
Lateralization of Language
Hypothesis
• Crow (1995)
• Suggests schizophrenia developed recently
– 100,000 - 150,000 years ago
• Linked to development of language
• Lateralization of language “centres”
– Left for semantics, phonetics; right for
emotional state identification
• Schizophrenics have atypical interaction
between hemispheres for language
processing
• Don’t process “sub-vocal” language as
normal
– Could explain delusions and auditory
hallucinations
Support?
• Indirect
– More left handed schizophrenics than usual
– Usual left hemisphere linguistic processing
often lost
– Speech output and input may be located in
opposite hemispheres in people with abnormal
handedness
• Speculative at this point
Issues
• Not all people with abnormal handedness
are schizophrenic
• Doesn’t explain why, evolutionarily, it
wouldn’t be selected against
– Crow argues it is a byproduct of human genetic
variability with respect to genes linked to
language
– Unclear if there could be any selective
advantage; creativity has been suggested, but
not well supported
Group-Splitting Hypothesis
• Stevens and Price (1996)
• Possible leadership value
• Disaffected individuals in group may look
for radical ideas from a leader to reform
societal rules
• The delusions, “unorthodox” ideas, and
charismatic focus may be appealing to those
looking for change
• Thus, schizophrenic is elevated to leader
• Confers fitness advantages
• There is historical precedence for radical
political, religious, ideological leaders to
attract followers, “groupies”; gain many
sexual opportunities
• Problems
– Historically rare, most schizophrenics are
actually not coherent or charismatic, don’t
know historic figures really were schizophrenic
Adaptive Paranoia
• Paranoid delusions frequent in
schizophrenics
• Development of genes for “suspiciousness”
may have been adaptive in EEA
– Reduce being cheated, avoid dangerous
situations, etc.
• But, full paranoid delusions more
debilitating than useful; why?
Psychopathy
• Antisocial personality disorder
• Lack of empathy, callous, exploit others
without feeling guilt or shame
• Prone to instant gratification
• May be quite charming and charismatic
• Machiavellian Intelligence
• Don’t lack ToM
Reciprocity
• Reciprocity important in social situations
• If most individuals are reciprocators, being
a cheater could be very adaptive
• But, only if numbers of cheaters remains
low
• Estimates that 3% of males and 1% females
are psychopaths, but that only half get
caught
– 50:50 success:failure may be self-regulating
• Politicians, business executives, lawyers…
Males
• To avoid being caught, move from group to
group
• Easier for males in EEA
• Freeloading may be a more adaptive
strategy for mobile males than females
Females
• Histrionic personality disorder
• Attention seeking, self-centred, narcissistic
• Not the same as psychopaths, but prone to social
defection
• More common in females than males
• Gain attention, resources, mating opportunities
with behaviour
• Frequently avoid reciprocating by feigned illness
Environment
• Mealey (1995)
• Predisposition toward psychopathy
• Environmental conditions drive individual
toward or away from predisposition