Chapter 12 Evolutionary Psychopathology and Darwinian Medicine Division

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 – A 1, A 2, 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 (~125 mya) • Primate ancestor very like modern tree shrew • Small insectivores • A meal for anything bigger www. hoglezoo. org/animals/view. php? id=183 en. wikipedia. org/wiki/Eomaia www. ryanphotographic. com/images/JPEGS/Tree%20 shrew. jpg

Benefit of Anxiety • Focuses attention • Prepares 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 To. M

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