9) Darwinian medicine: what is evolutionary medicine and psychiatry?

What is the difference between Evolutionary medicine & conventional medicine?

Conventional

• aetiology of ilnesses = immediate causes

• pathogenesis = mechanisms of ilnesses in the body

→ proximate ‘what’ and ‘how’ explanations

Evolutionary

• why do we have certain health problems

  • why natural selection has not weeded them out

• can symptoms of ilnesses be functional?

• can we treat ilnesses more effectively by understanding their evolutionary roots?

→ ultimate ‘why’ explanations

What is the counterintuitive conclusion from Darwinian medicine

Sometimes unpleasant symptoms need to be respected, and should not even be treated, bcs have a function!

infectious diseases are caused by …

various pathogens: viruses, bacteria, protozoan, parasites, fungi and prions

For hom many deaths do communicable diseases count annually

communicable diseases = besmettelijke ziekten

± 25%

What are the deadliest infections

1. acute lower respiratory tract infections = 2.6 million

2. Neonatal conditions: 2 million

3. Diarrhoeal diseases: 1.5 million

4. Tuberculosis: 1.4 million

5. HIV/AIDS: 690 000

6. Malaria: 409 000

Viruses, bacteria and parasites as ‘secret agents’

they cause millions cases of cancer and have long-term adverse effects 

• eg. COVID-19 → lung damage, chronic fatigue syndrome

Leading causes of death in high vs low income countries

high income 

• chronic diseases

  • non communicable (niet besmettelijk)

  • nr 1 = heart disease 

  • nr 2 = Alzheimer

• only 1 infectious disease in top 10: lower respiratory infections (nr 6)

• 1/100 deaths < 15y

low income

• infectious diseases (nr 1 = neonatal)

  • 1/3 of all deaths

• 40/100 deaths < 15y

→ Why has natural selection not weeded out such diseases from the population?

evolutionary arms race against infectious diseases

host’s adaptations aim to protect the host: destroy the pathogen and expel it from the body

Pathogen’s adaptations aim to increase copies of the pathogen

→ Host can never win

Why can the host never win the evolutionary arm race against the pathogen?

asymmetry in life-cycle time (mutation rate)

• host = long lived organisms <=> pathogen = short

  • pathogens reproduce quickly

    • => in each generation there is always the possibility for new mutations that can comprimise the host immune system

    • => host cannot adapt quickly enough to the new mutations

symptoms of infectiours ilnesses

1. adaptations to destroy the pathogen = vital function

• makes the patient feel bad but avoid the pathogen of making copies of itself

2. adaptations of the pathogen to aid its transmission

What is a major cause of the antibiotic resistance crisis

uncontrolled and inappropriate use of antibiotics globally

• antibiotics kill the majority of bacteria but there might always be some survivors who mutate & create a strain that is resistent to the antibiotic

  • => when we increase the amount of antibiotic there might be new mutations that can tolerate antibiotic levels 1000X stronger than that the origanal strain could tolerate

• doctors have been adviced to consider when antibiotics are really needed

Fever and temporary anemia (tijdelijke bloedarmoede)

Aim to protect the host against the pathogen (system 1)

• viruses and bacteria require stabile temperature to function + iron to multiply

  • → fever and reduction in blood iron kill viruses and bacteria

  • medication (antipyretics that suppress fever / iron supplements) provide an advantage to microbes during infection 

    • help them produce copies

    • Can they prolong recovery?

sneezing and coughing

chances to get to another host increase

Give a case were symptoms benefit both the host and the pathogen

sneezeing

• virus spreads (good for pathogen)

• virus expels (good for host)

Ophiocordyceps unilateralis

= insect-pathogenic fungus → infects ants in tropical rain forests:

• ants picks up the fungus 

  • fungul cell population growth besides the ants brain

  • leaves their nest to go close to the floor where temp. and humidity are suitable for fungal growth

• Ants use their mandibles muscle to attech themselves to a leave (4-10d) → lockjaw behavior

• relaese fungus's spores

note: healthy ants can sense which individuals are infected → carry them down from the trees to avoid infecting the whole colony

Toxoplasma

can only reproduce sexually in feline intestine (kattendarm)

• in infected rats and mice, risk taking behavior increase 

  • no avoidance of places that smell like cat urine, less neophobia

  • → likelyhood to end up eaten by a cat increases

  • →  Cats get infected from the meat, and the toxoplasm can again reproduce sexually

Toxoplasmosis in humans

common (10-60% carry the protozoan)

symptoms: flue-like

Main routes of transmission

1. food-human (undercooked meat and shelfish, contaminated water)

2. animal-human (eg. cleaning feces of the cat)

3. mother-child

trend: pp with latent toxoplasmosis perform worse in psychomotor tests, take more risks, more often involved in traffic accidents, and conduct suicides more often

• <=> recent study: difference between infected and non-infected only found in suicide attempt rates (trend)

morning sickness in pregnant woman → ilness vs adaptation?

strongest during first trimester when the development of the embryo is fastest

good correlation between toxin concentrations in foods and the tastes and odors that cause revulsion (afkeer)

• barbiqued meat, certain roots and vegetables

• Aversion to meat also could help to avoid toxoplasmosis which is dangerous for developing foetus

Women who show little / no signs of morning sickness : p(miscarry) increases

→ function of morning sickness = protect the developping embryo

• not only a side-effect

• don’t treat it

Why are late-age ilnesses such as alzheimer not weeded out by natural selection?

Natural selection is unable to weed out genes that have already been passed on

=> Could there advatages of carrying genes for the illness before the symptom onset (early in life)?

definition of emotions

physiological, cognitive and behavioral responses to internal or external events

• proximate explanations → explains how & what but not why

Why have emotions evolved

They are specialized states that adjust behavior to meet adaptive challenges

→ adaptations that guide behavior 

• result of natural selection

• each emotion has its own function (?)

Are emotions universal?

yes (underlying feeling), but their appearance and expression is guided by environmental factors : experience and cultural display rules

Do we recognise emotions in other humans and/or species

humans: yes → facial expressions are universally well recognized

species: often misinterpretations

• as humans we have the tendency to antropomorphise (= see human characters in other animals)

Functions of emotions

negative = avoid, attack, minimize costs

• eg. fear, anger, hatred, sadness, disgust…

• more abundant (overvloeding) and specific

positive = approach, seize the opportunity

• eg. joy, contentment, affection and love, interest

• less abundant, more general

→ neg emotions = defences <=> pos = incentives

“if it feels good do it again; if it feels bad, avoid doing it again”

Why are negative emotions more abundant and specific

In EEA more specific threats and more dire consequences if ignored

<=> pos emotions: in EEA less opportunities than threats

Why are mental health problems not been weeded out by natural selection?

psychological pain & suffering may not be fun but in some cases they may be adaptive

psychological and psychiatric problems may follow from… (6)

1. normal functioning of the defence system

• compromise between inclusive fitness and psychiological well-being

2. normal distribution of polygenic traits in the population includes extremes

• trait variation

3. Adaptations that functioned well in the ancestral past but fail in current environment

• mismatch / time lag hypoth.

4. pleiotropy: alleles that increase inclusive fitness but also predispose to psychiatric problems

• gene with different functions

• benefits outweigh the costs

5. frequency dependent selection

6. combination of the above

What are anxiety and fear?

anxiety = a worry about future events

fear = a reaction to current events

→ normal and usuful reactions, adaptive in many situations

What effect have anxiety and fear?

When faced with a threat they alter our thinking, physiology and behavior:

• Physiological changes:

  • Adrenalin secretion → glucose (energy) is directed to the muscles → quicker & faster escape

  • heart rate → blood circulation to muscles

  • breathing rate → more oxygen available

• Reaction times (fight or flight)

• Attentional shift (narrowing of focus)

• Learning and conditioning

  • more prepared to face similar types of threats in the future

    • = core of anxiety

anxiety disorders (12%) - smoke detector principle

better to react to false alarm repeatedly than ignore a real warning once

• low levels of anxiety → long-term survival is reduced

  • more engaged in dangerous activities

mismatch hyp. for anxiety disorders

mismatch between currend and past environment

• ancestors: frequently exposed to different types of threats but did not learn of the existence of unpredictable rare, unlikely threats

• today: media exposes us to all kind of threats but personal exposure is rare

  • + social life has changed: loss of tight family groups, surrounded by strangers → insecurity about our status & role in the group

Modern epidemic of major depressive disorder

symptoms: low mood, low self-esteem, loss of interest in normally enjoyable activities, low energy and pain without a clear cause

leading cause of disability worldwide

also increases risks of deaths by accidents and ilnesses

reactive depression vs major depressive disorder

reactive = normal defensive reaction to live events (eg. loss) → adaptive?

major (clinical) = predisposition to feel depressed

• without triggering events or as an oversized and extended reaction to normal losses and disappointments (pathological)

depression as a normal adaptive reaction

SOCIAL COMPETITION HYP.

• depressive state evolved in relation to social competition

  • unconscious, involuntary losing strategy

    • giving up & accepting that someone is better = voluntary yielding

• prolonged depression when winning is impossible, but yielding is not voluntary

  • conflict: over behavior (yielding) vs internal state (desire to win)

COMMON PROXIMATE MECHANISMS FOR DEPRESSION WITH OTHER PRIMATES?

• vervet monkeys: alpha males in each group have twice the levels of serotonin as low-ranking males

• Low serotonin levels are often linked to feelings of depression.

depression: mismatch and social competition

mismatch between modern environment and EEA

• Modern lifestyle

  • sedentary lifestyle, overfeeding, reduced food quality, reduced sunlight exposure, sleep deprivation and social isolation, can exacerbate depressive symptoms

• Social environment

  • loss of support networks

    • contact but no physical presence

  • mass communication and change in the comparison groups

    • we compare ourselfs with the most succesful → perceived loss of status, unrealistic expectations and lowered self esteem

subtyping depression

Critique on how depression is treated nowdays: independent of the causes of depressive symptoms individuals are threated in the same manner (= antidepression that affect neuromodulation in the brain + psychotherapeut)

• <=> With subtypes more effective LT treatments are possible bcs different subtypes have different causes & thus need different treatment

eg. Modern lifestyle increases susceptibility to inflammatory dysregulation and chronic stress

• both increase the amount of proinflammatory cytokines in peripheral blood, leading to low mood

evolutionary informed treatment for depression

if ancestral humans were not prone to prolongued depression states could we learn something from their life style that could eleviate depressive symptoms in modern humans?

• 14week treatment that mimics the conditions under which our ancestors lived:

  • increasing the amount of sunlight

  • boosting the amount of omega-3 fatty acid in the diet

  • spending more time with friends and family 

  • outdoor pursuits

  • sleep patterns more in tune with ancestral habits 

• finding: 75.3% success rate

  • but is the possible in the modern environment…?

Unipolar vs bipolar depressive disorder

unipolar: mood fluctuates between normal and depressed

bipolar: mood fluctuates between normal, depressed and manic

• manic: ‘high’ → increased energy, craving activities, racing thoughts and ideas, feeling ‘super’ powers

• prevelance = 1%

• strong genetic component → heritability 40%

bipolar disorder = pleiotropy?

bipolar disorder follows from having alleles that may increase inclusive fitness but predispose to depression

• benefits to relatives who are unaffected by bipolar disorder

  • benefits: creativity → relatives work more often in creative professions

• “mad genius-argument”: bipolar disorder is more prevelant in artistic and creative personalities and they are most creative during the manic state

  • benefits (creativity during manic episode) > loss (depression)

  • eg. Vincent van Gogh

Schizophrenia

severe split from reality: hallucinations, delusions, thought disturbances

• hallucinations are most of the time auditory (hearing voices)

• affective disorders: innapropriate emotional responses, socially withdrawn, difficulties with maintaining relationships…

  • => how can schizophrenia maintain in the population if it endangers survival & reproductive succes???

• Prevalence 1%

Strong geneticcomponent: heritability41-87%

Which psychiatric disease is difficult to explain with an evolutionary theory? (+ suggestion)

schizophrenia: strong reproductive disadvantage but high heritability

suggestion: pleiotropy

• Close kin of schizophrenics work in creative professions twice as often as relatives of healthy individuals

• → creativity might be the benefit that is provided by those alleles that also predispose to schizophrenia

Two hypotheses for the cause of chizophrenia

Abnormal lateralisation of language => inability to dissociate external voices from internal language

• side-effect of abnormal neurodevelopment

Social brain hyp.

• we constantly attribute meaning to the actions of others => schizophrenia = extreme form of extracting meaning

Personality disorders

the extremes of forms of tought and behavior we all have

Antisocial personality disorder

Disregard for or violation of the rights of others + a weak moral sense

• lack of depth of feelings of shame, guilt or empathy

heritability ± 40

Is psychopathy = antisocial personality disorder

NO → they overlap, but they are distinguishable

Typical features of ASPD

• Inability to function in accordance with social norms or laws

• Irresponsibility, impulsivity, and inability to plan for distant future

• Carelessness of one’s own and others’ safety

• Manipulation, lying, cheating for one’s own benefit or pleasure

• Lack of remorse, lack of empathy, inability to understand the feelings of others

• Narcissism

• Superficial charm

ASPD - frequency dependent selection

NEGATIVE frequency dependent selection : “ultimate cheaters”

• cheating = excellent strategy when majority of the population are altruistic and act according to the tit for tat strategy => cheating can increase reproductive succes

note: works better in males bcs when they are detected they can easily move to another group

two theories for psychopathy

1. balancing: different levels of psychopathic traits depend on the social environment

• eg. small vs large societies → small: cheating easily detected → psychopathy is less likely

2. shifting: all individuals have the potentional to develop psychopathic traits under certain environmental conditions

Do all psychiatric conditions necessarily have an ultimate level of explanation?

NO

• All behavior must have proximate causes – but all behavior does not need to have ultimate causes!

• Sometimes human physiological and psychological systems become dysfunctional, and things just go wrong

• All behaviors are not (by-products off) adaptations!