Title: Evolutionary Psychopathology and Darwinian Medicine
1Chapter 12
- Evolutionary Psychopathology and Darwinian
Medicine
2Division
- Evolutionary Psychopathology
- Study of mental illness within an evolutionary
context - Darwinian Medicine
- Evolutionary theory applied to both psychiatric
and non-psychiatric health issues
3Levels
- Traditional
- Proximate
- Etiology (cause) and pathogenesis (mechanism)
- How questions
- Evolutionary medicine
- Ultimate
- Why questions
4Parasites and Hosts
- Arms race
- Red Queen theory
- Adaptation and counter adaptation
5Symptoms
- 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
6Bacterial 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
7Cholera (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
8Bubonic 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
10Viral 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
11Ebola
- 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
12Parasite/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
13Immune 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
14Complexity
- 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
15MHC
- Major histocompatibility complex (MHC)
- Genes
- Code for disease detectors (antibodies) in the
immune system - In humans
- Human leukocyte antigen (HLA)
16In 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
17In Humans
- Dont usually smell pee...
- Sweat
- MHC
- Saliva?
- Kissing?
18Claus 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
19Womens Sense of Smell
- Most sensitive during ovulation
- Conception
- Contraceptive pill
- Interferes with sense of smell
- In Wedekinds study, no correlation between
preferences and MHC
20HLAs
- 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?)
21MHCs 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
22Blood 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
23Hutterites of North Dakota
- Small communities
- Not much outbreeding
- Marriages of people with matched MHCs
- Fewer pregnancies
- More miscarriages
24Psychiatric Problems
- Psychiatric disorders not (usually) due to
parasites - Genes and/or environmental effects
- Why hasnt evolution selected against them?
25Pleiotropy 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
26Time 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
27Compromise 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
28Trait 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
29Anxiety
- Very basic and adaptive
- Feeling of apprehension, nervousness
- Xenophobia
- Very, very ancestral
30Mammals
- 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
31Benefit 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
32Evolved 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.
33Anxiety 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)
34Depression
- 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
35Ultimate 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
36Developmental 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
37Ultimate-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
38Serotonin
- 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
39Possible 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
41Schizophrenia
- 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
42Genetics
- 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)
43Diathesis-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
44Lateralization 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
46Support?
- 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
47Issues
- 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
48Group-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
50Adaptive 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?
51Psychopathy
- 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
52Reciprocity
- 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
53Males
- 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
54Females
- 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
55Environment
- Mealey (1995)
- Predisposition toward psychopathy
- Environmental conditions drive individual toward
or away from predisposition