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Evolutionary Psychopathology and Darwinian Medicine

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Title: Evolutionary Psychopathology and Darwinian Medicine


1
Chapter 12
  • Evolutionary Psychopathology and Darwinian
    Medicine

2
Division
  • Evolutionary Psychopathology
  • Study of mental illness within an evolutionary
    context
  • Darwinian Medicine
  • Evolutionary theory applied to both psychiatric
    and non-psychiatric health issues

3
Levels
  • Traditional
  • Proximate
  • Etiology (cause) and pathogenesis (mechanism)
  • How questions
  • Evolutionary medicine
  • Ultimate
  • Why questions

4
Parasites and Hosts
  • Arms race
  • Red Queen theory
  • Adaptation and counter adaptation

5
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

6
Bacterial Infection
  • Single celled microbes
  • Leukocyte endogenous mediator (LEM) released by
    body when infected with bacteria
  • Raises body temperature
  • Iron withdrawal from bloodstream (into liver)
  • Symptomatically --gt fever and fatigue
  • Bacteria need iron to reproduce and are
    susceptible to higher temperatures
  • Treatment of fever and iron supplements counter
    bodys evolved defenses

7
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

8
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
9
  • 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
10
Viral Infections
  • Submicroscopic strands of DNA or RNA
  • Assisted self-replicating infectious agent
  • Need another organisms cells to reproduce
  • Obligate parasites
  • E.g., rabies, yellow fever, smallpox, West Nile,
    herpes

11
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
12
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

13
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

14
Complexity
  • Millions of different antigens
  • Lock (antibody) and key (antigen) analogy
  • Cant 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

15
MHC
  • Major histocompatibility complex (MHC)
  • Genes
  • Code for disease detectors (antibodies) in the
    immune system
  • In humans
  • Human leukocyte antigen (HLA)

16
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

17
In Humans
  • Dont usually smell pee...
  • Sweat
  • MHC
  • Saliva?
  • Kissing?

18
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

19
Womens Sense of Smell
  • Most sensitive during ovulation
  • Conception
  • Contraceptive pill
  • Interferes with sense of smell
  • In Wedekinds study, no correlation between
    preferences and MHC

20
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?)

21
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
    others defenses

22
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 doesnt O vanish from population?
  • Malaria
  • Type O more resistant
  • Also, maybe less likely to get some cancers

23
Hutterites of North Dakota
  • Small communities
  • Not much outbreeding
  • Marriages of people with matched MHCs
  • Fewer pregnancies
  • More miscarriages

24
Psychiatric Problems
  • Psychiatric disorders not (usually) due to
    parasites
  • Genes and/or environmental effects
  • Why hasnt evolution selected against them?

25
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

26
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

27
Compromise Argument
  • Design compromises, not genetic flaws
  • Selective pressures act on inclusive fitness
  • Evolution doesnt act to design optimal systems
  • Sufficient degree of differential reproductive
    success is the requirement

28
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

29
Anxiety
  • Very basic and adaptive
  • Feeling of apprehension, nervousness
  • Xenophobia
  • Very, very ancestral

30
Mammals
  • Eomaia (125mya)
  • Primate ancestor very like modern tree shrew
  • Small insectivores
  • A meal for anything bigger

en.wikipedia.org/wiki/Eomaia
www.ryanphotographic.com/images/JPEGS/Tree20shrew
.jpg
www.hoglezoo.org/animals/view.php?id183
31
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

32
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.

33
Anxiety Disorders
  • Time lag
  • Havent 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)

34
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

35
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

36
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

37
Ultimate-Proximate Interactions
  • 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

38
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

39
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

40
  • 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

41
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

42
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)

43
Diathesis-Stress Model
  • Doesnt follow strict Mendellian rules
  • Individual may have genes for schizophrenia, but
    only phenotypically express them after
    particularly stressful life event
  • Genes create predisposition

44
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

45
  • Schizophrenics have atypical interaction between
    hemispheres for language processing
  • Dont process sub-vocal language as normal
  • Could explain delusions and auditory
    hallucinations

46
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

47
Issues
  • Not all people with abnormal handedness are
    schizophrenic
  • Doesnt explain why, evolutionarily, it wouldnt
    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

48
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

49
  • 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, dont know
    historic figures really were schizophrenic

50
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?

51
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
  • Dont lack ToM

52
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
  • 5050 successfailure may be self-regulating
  • Politicians, business executives, lawyers

53
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

54
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

55
Environment
  • Mealey (1995)
  • Predisposition toward psychopathy
  • Environmental conditions drive individual toward
    or away from predisposition
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