View
231
Download
1
Tags:
Embed Size (px)
Citation preview
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– 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
• 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
en.wikipedia.org/wiki/Eomaia
www.hoglezoo.org/animals/view.php?id=183www.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
• 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