Evolutiepsychiatrie: een inleiding Vakgroep Wijsbegeerte en Moraalwetenschap

1. Evolutiepsychiatrie: een inleiding Vakgroep Wijsbegeerte en Moraalwetenschap Pieter R. Adriaens – KUL / FWO

2. Overzicht 1. Inleiding: een waanzinnig raadsel 2. De geschiedenis van de evolutiepsychiatrie 3. Enkele verklaringsmodellen 4. Waarom evolutiepschiatrie? 5. Besluit

3. InleidingGeschiedenis Modellen Relevantie Besluit 1. Inleiding: een waanzinnig raadsel • Geestesziekten zijn van alle tijden • Geestesziekten zijn overerfbaar • Geestesziekten komen relatief vaak voor • Geestesziekten zijn nefast voor het RS • Hoe ontsnappen gekke genen aan natuurlijke selectie?

5. InleidingGeschiedenis Modellen Relevantie Besluit 2. Geschiedenis van de evolutiepsychiatrie • Sir James Crichton-Browne (1840-1937) • Sigmund Freud (1856-1939) • Sir Julian Huxley (et al.) (1887-1975) • John Price (1930-) • Hedendaagse evolutiepsychiatrie (1975-)

6. InleidingGeschiedenis Modellen Relevantie Besluit Sir James Crichton-Browne (1840-1937) • Belangrijke bijdrage aan Darwins The Expression of the Emotions in Man and Animals (1872) • Uitgebreide correspondentie (zie DCP), met bemiddeling van Dr. Henry Maudsley • Evolutionaire frenologie: • ‘It seemed not improbable that the cortical centres which are last organised, which are most highly evolved and voluntary, might suffer first in insanity’ (Crichton-Browne 1879)

7. InleidingGeschiedenis Modellen Relevantie Besluit Sigmund Freud (1856-1939) • Engelse vertaling: A Phylogenetic Fantasy (1985 [1915]) • Verband tussen de wederwaardigheden en emoties van onze voorouders tijdens laatste ijstijd, en onze vatbaarheid voor neurosen en psychosen • Psycho-lamarckisme: geloof in overerfbaarheid van verworven psychische toestanden, zoals emoties (Sulloway 1979) • Geestesziekten als mismatches

8. InleidingGeschiedenis Modellen Relevantie Besluit Sir Julian Huxley (1887-1975) et al. • Schizophrenia as a genetic morphism (1964) • Schizofrene patiënten hebben een reproductief nadeel • Mogelijke compenserende voordelen: weer-stand tegen infectieziekten, boven-gemiddelde vruchtbaarheid van vrouwelijke patiënten/vrouwelijke verwanten van patiënten,... • Geestesziekten als deel van packagedeal

9. InleidingGeschiedenis Modellen Relevantie Besluit John Price (1930-) • Dominance hierarchy and the evolution of mental illness (1967) • Depressie als signaal van onderwerping, een adaptatie aan levensomstandigheden in het Paleolithicum • ‘The ideas of inferiority and unworthiness, the withdrawal, the loss of appetite and libido: these might have been designed to prevent an individual from desiring and attempting to regain former status’ (Price 1967) • Geestesziekten als adaptaties

10. InleidingGeschiedenis Modellen Relevantie Besluit Hedendaagse evolutiepsychiatrie

11. De hamvraag (opnieuw) • Evolutionaire geneeskunde: Why we get sick • ‘If natural selection is so powerful that it can shape bodies so perfect in so many respects, then why are our bodies also full of so many flaws and design oversights that leave us vulnerable to thousands of diseases?’ (Nesse & Williams 1999) • Evolutionaire psychiatrie: Why we get mad • ‘How come natural selection has not yet eliminated mental disorder genes if they have been around for thousands of years already, and if they simply crush the reproductive success of their carriers?’

12. InleidingGeschiedenis Modellen Relevantie Besluit 3. Enkele verklaringsmodellen • Het mismatch-model • Het adaptationistisch model • Het trade-off model • Het polygeen mutatie-selectie model • Het kanker-model

13. InleidingGeschiedenis Modellen Relevantie Besluit Het mismatch-model • Some mental disorders result from a genome lag (McGuire & Troisi 1995; Stevens & Price 1996) or a mismatch between the environment we evolved to live in (EEA) and our current environment • Examples: anxiety disorders (Marks & Nesse 1994), eating disorders, toxicomania (Williams & Nesse 1991) • Most mental disorder traits (e.g. anxiety) show a continuously distributed phenotypic (and genetic?) variation. Individuals towards the sensitive end of the distribution might have functioned normally in the EEA • Medical examples: tooth decay & diabetes

14. InleidingGeschiedenis Modellen Relevantie Besluit The adaptationist model • Some mental disorders are adaptations even in the current environment (versus mismatch-model: mental disorders were only adaptive in the EEA) • Examples: depression (see next page), especially postpartum depression (Hagen 1999); psychopathy (Mealey 1995) • Thus mental disorders may simply stress the fact that people, like all complex adaptive systems, are not evolved to maximize health, but to have descendants (Chisholm & Burbank 2001) • Medical examples: fever, pain, nausea and vomiting

15. InleidingGeschiedenis Modellen Relevantie Besluit The adaptationist model (continued) • What’s the use of depression? • Communicating a genuine need for help (Lewis 1934) • Signaling yielding in a hierarchy conflict (Price 1967) • But: • Is depression an adaptation, or was it (and if so, when did it cease to be adaptive)? • Is/was depression an adaptation (low mood) or an adaptation gone wild (dysfunction of low mood)? • And: • Do the symptoms of low mood/depression match their function? Do depressive symptoms enable us to cope with socially difficult situations? • Are all depressions functional?

16. InleidingGeschiedenis Modellen Relevantie Besluit The trade-off model • Some mental disorders are part of a trade-off (Nesse 2005), aka a packagedeal (Adriaens 2006), aka a (balanced) (poly)morphism (Huxley et al. 1964) in which the adaptive advantages somehow counterbalance the costs inflicted by the MD • Different modalities: overdominance/heterozygote advantage (Huxley et al. 1964) or sexually antagonistic selection (Avila et al. 2001) • Examples: schizophrenia (e.g. Carter & Watts 1971; Allen & Sarich 1988; Crow 2000; Horrobin 2001; Nettle 2001) and bipolar disorder (Jamison 1993) • Medical example: sickle-cell anaemia

17. InleidingGeschiedenis Modellen Relevantie Besluit The trade-off model (continued) • What’s the use of schizophrenia? • Patients or their relatives? • Physiological advantages: • Enhanced resistance to surgical and wound shock, pain, infectious diseases, allergies (dermatitis, asthma, pollinosis, urticaria,…), high doses of histamine, etcetera (Huxley et al. 1964; Erlenmeyer-Kimling 1968; Carter & Watts 1971) • Enhanced fertility of female relatives of schizophrenics (Avila et al. 2003) • Psychological advantages: • Enhanced social cognition (Burns 2004) or linguistic (Crow 2000) abilities • Enhanced creativity of (some) schizophrenic patients and/or their relatives (e.g. Karlsson 2001; Nettle 2001; Horrobin 2001)

18. InleidingGeschiedenis Modellen Relevantie Besluit The polygenic mutation-selection model • Some mental disorders are genuine dysfunctions, reflecting the mutational loadon the thousands of genes underlying human behavior (Keller & Miller 2006) • Mental disorders are maladaptive (versus the adaptationist model), and have always been maladaptive (versus the mismatch-model) • Mutational load is highly variable, and individuals with a high load of mutations would be at a higher risk of having mental disorders • Examples: severe mental disorders (e.g. schizo-phrenia, mental retardation; Keller & Miller 2006)

19. InleidingGeschiedenis Modellen Relevantie Besluit The PMSM (continued) • The most Darwinian model of all evolutionary psychiatric models: variation in natural world ˜ variation in psychiatric population ˜ genetic variation • Revival of dimensional perspective in psychiatry: • ‘Everyone alive, according to this [PMS] model, has minor brain abnormalities that cause them to be a little bit mentally retarded, a little bit emotionally unstable, and a little bit schizophrenic’ (K & M 2006) • The number of MD genes is far higher than psychiatric geneticists tend to think, and their effect size is much smaller • But: why do diagnostic categories exist at all?

20. InleidingGeschiedenis Modellen Relevantie Besluit The cancer-model • Some mental disorders persist because their symptoms only show up after the reproductive period • Example: Huntington’s disease (Nesse 2002) • Note: models are not mutually exclusive • Full-blown schizophrenia might be due to reduced intake of particular essential fatty acids (mismatch model) • Schizotypics may have been shamans, mystics or visionary artists (adaptationist model) • Full-blown schizophrenia may persist because of its link to creativity (trade-off model)

21. InleidingGeschiedenis Modellen Relevantie Besluit 4. Waarom evolutiepsychiatrie? • Therapeutical/diagnostic relevance: • Understanding a dysfunction in a cognition/emotion/behavior requires an understanding of its function (e.g. affective disorders) • A critique of DSM-III and DSM-IV: symptoms are not (necessarily) diseases (Nesse & Jackson 2007) (but: the smoke detector principle) • An example: the mix-up between sadness and depression (Wakefield & Horwitz 2007) • Theoretical relevance: • Guiding research (e.g. the implications of the PMS-model for the future of psychiatric genetics) • Providing an integrative theoretical framework (a genuine biopsychosocial model of mental disorders)

22. InleidingGeschiedenis Modellen Relevantie Besluit 5. Besluit • MD susceptibility genes should have been weeded out already, and yet they persist... How come? • 1. because our current environment differs from our EEA; 2. because MD are defenses, rather than diseases; 3. because MD genes also code for some adaptive advantage; 4. because MD genes are too many & their effect size is too small • Evolutionary psychiatry may generate important tools to think about psychiatric diagnostics, therapeutics, and theory.

23. Dank!