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

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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

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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

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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

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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

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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
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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

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• 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

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• 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