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