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Overview

Overview. Presentation 1 (April 20, 2007) Evolutionary psychiatry: an introduction Presentation 2 (TBC) Evolutionary psychiatry and the schizophrenia paradox: a critique. Evolutionary psychiatry: an introduction. 1. Darwin and the health sciences

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Overview

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  1. Overview • Presentation 1 (April 20, 2007) • Evolutionary psychiatry: an introduction • Presentation 2 (TBC) • Evolutionary psychiatry and the schizophrenia paradox: a critique Evolutionary psychiatry: an introduction

  2. Evolutionary psychiatry: an introduction 1. Darwin and the health sciences 2. A short history of evolutionary psychiatry 3. How to survive as a mental disorder 4. Philosophy and evolutionary psychiatry 5. Conclusion Evolutionary psychiatry: an introduction

  3. IntroductionHistory Models Philosophy Conclusion 1. Darwin and the health sciences • Darwinian medicine: 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) • Darwinian psychiatry: 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?’ Evolutionary psychiatry: an introduction

  4. Introduction History Models Philosophy Conclusion 2. A short history of evolutionary psychiatry • Sir James Crichton-Browne • Sigmund Freud • Sir Julian Huxley et al. • John Price • Contemporary evolutionary psychiatry Evolutionary psychiatry: an introduction

  5. Introduction History Models Philosophy Conclusion Sir James Crichton-Browne (1840-1938) • Major contribution to Darwin’s The Expression of the Emotion in Man and Animals (1872) • Evolutionary phrenology: emphasis on the link between cerebral symmetry and insanity (and the faculty of language; Crow 1997) • ‘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) • Mental disorders as novelties Evolutionary psychiatry: an introduction

  6. Introduction History Models Philosophy Conclusion Sigmund Freud (1856-1939) • A Phylogenetic Fantasy (1985 [1915]) • Linking up the vicissitudes and (now useless) emotions of our ancestors during the last ice age with our disposition towards the neuroses and the psychoses • Psycholamarckism: a belief in the inheritance of acquired mental states (e.g. emotions) (Sulloway 1979) • Mental disorders as mismatches (cfr Cosmides & Tooby (1997): ‘our modern skulls house an ice age mind’) Evolutionary psychiatry: an introduction

  7. Introduction History Models Philosophy Conclusion Sir Julian Huxley (1887-1975) et al. • ‘Schizophrenia as a genetic morphism’ (Nature, 1964) • Schizophrenics are at a selective disadvantage • Possible compensatory advantages: enhanced resistance to infectious diseases, above average fertility of female schizophrenics,… • If schizophrenia is due to a ‘single gene with low penetrance’, if ‘its incidence is at least 1 per cent in all racial and ethnic types’, and if the fertility of schizophrenics is drastically reduced, than the illness provides evidence of a ‘balanced [poly]morphism’ (Huxley et al. 1964) • Mental disorders as trade-offs Evolutionary psychiatry: an introduction

  8. Introduction History Models Philosophy Conclusion John Price (1930-) • ‘The dominance hierarchy and the evolution of mental illness’ (Lancet, 1967) • Depression as a ‘yielding response’, a behavioral adaptation to life conditions in the Paleolithic (and now?) • ‘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) • Mental disorders as adaptations Evolutionary psychiatry: an introduction

  9. Introduction History Models Philosophy Conclusion Contemporary evolutionary psychiatry Evolutionary psychiatry: an introduction

  10. Introduction History Models Philosophy Conclusion 3. How to survive as a mental disorder • The mismatch-model • The trade-off model • The adaptationist model • The polygenic mutation-selection model • Some minor models Evolutionary psychiatry: an introduction

  11. Introduction History Models Philosophy Conclusion The central paradox (again) • The question: • ‘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?’ • The answers… Evolutionary psychiatry: an introduction

  12. Introduction History Models Philosophy Conclusion The mismatch-model • Some mental disorders result from a genome lag (McGuire & Troisi 1995; Stevens & Price 1996) or a mismatch (Murphy 2005) between the environment we evolved to live in (EEA) and our current environment • 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 • Examples: eating disorders, toxicomania (Williams & Nesse 1991), anxiety disorders (Marks & Nesse 1994) • Medical example: appendix Evolutionary psychiatry: an introduction

  13. Introduction History Models Philosophy Conclusion 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) • 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 Evolutionary psychiatry: an introduction

  14. Introduction History Models Philosophy Conclusion The adaptationist model • Some mental disorders are adaptations even in the current environment (versus mismatch-model: mental disorders were only adaptive in the EEA) • 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) • Examples: psychopathy (Mealey 1995), postpartum depression (Hagen 1999), depression (see next page) • Medical examples: fever, pain, nausea and vomiting Evolutionary psychiatry: an introduction

  15. Introduction History Models Philosophy Conclusion The adaptationist model (continued) • Possible functions of depression: • Communicating a need for help (Lewis 1934) • Signaling yielding in a hierarchy conflict (Price 1967) • Regulating patterns of investment (Nesse 1990) • Important preliminary issues: • 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 (depression) (or a defect)? • Other important issues: • 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? Evolutionary psychiatry: an introduction

  16. Introduction History Models Philosophy Conclusion The polygenic mutation-selection model • All mental disorders are genuine dysfunctions, reflecting the mutational load on 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) • ‘Darwinian psychiatrists (…) often go to torturous lenghts to find hidden adaptive benefits that could explain the evolutionary persistence of profoundly harmful mental disorders such as schizophrenia or anorexia, but these accounts are often frustratingly implausible or hard to test’ (Keller & Miller 2006) • Examples: severe mental disorders (e.g. schizo-phrenia, mental retardation; Keller & Miller 2006) Evolutionary psychiatry: an introduction

  17. Introduction History Models Philosophy Conclusion The polygenic mutation-selection model (continued) • Average (minor) mutational load: 500-2000 older mutations/person, half of which are expressed in the human brain • ‘Selection removes harmful mutations at a rate proportional to the fitness cost of the mutation’ (Keller & Miller 2006). Sometimes it takes tens of generations to get rid of a slightly harmful mutation • Like most traits, mutational load is highly variable • Thus: • ‘The end result will be continuous distributions with respect to almost all psychological dimensions. Individuals with a high load of mutations would be at a higher risk of having mental disorders, and would tend to pass this risk on to their offspring’ (Ibid.) Evolutionary psychiatry: an introduction

  18. Introduction History Models Philosophy Conclusion The polygenic mutation-selection model (continued) • Keller & Miller’s watershed model of mental disorders: Evolutionary psychiatry: an introduction

  19. Introduction History Models Philosophy Conclusion Some minor models • Novelty-model: some mental disorders result from novel developments in our evolutionary history, and they persist because selection simply did not have the time yet to weed them out • Example: viral accounts of schizophrenia (Ledgerwood et al. 2003); depression as psychological malfunction (Murphy 2005) • Cancer-model: some mental disorders persist because their symptoms only show up after the reproductive period • Example: Huntington’s disease (Nesse 2002) Evolutionary psychiatry: an introduction

  20. Introduction History Models Philosophy Conclusion ! Models are not mutually exclusive ! • Example: David Horrobin’s evolutionary account of schizophrenia (Horrobin 2001) • Schizophrenia is a fairly recent disorder vis-à-vis its subclinical version, schizotypy (novelty-model) • The first schizotypics may have been shamans or priests (adaptationist model) • The detrimental effects of full-blown schizophrenia may be balanced by our dazzling creativity (trade-off model) Evolutionary psychiatry: an introduction

  21. Introduction History Models Philosophy Conclusion 4. Philosophy and evolutionary psychiatry • Evolutionary psychiatry’s contribution to philosophy • Philosophy’s contribution to evolutionary psychiatry Evolutionary psychiatry: an introduction

  22. Introduction History Models Philosophy Conclusion Evolutionary psychiatry’s contribution to philosophy • Preparation of an edited volume on the philosophy of evolutionary psychiatry (De Block & Adriaens, under review), with contributions about: • The nature and scientific status of evolutionary psychiatry • The relevance of Darwinian considerations in the debate about the nature and classification of mental disorders (philosophy of psychiatry) • The implications of evolutionary psychiatry for our very humanity • An example: evolutionary psychiatrists suggest that man’s vulnerability to mental disorders may well be one of his defining features in the animal kingdom (Adriaens 2003) Evolutionary psychiatry: an introduction

  23. Introduction History Models Philosophy Conclusion Philosophy’s contribution to evolutionary psychiatry • A contribution to the debate on the evolution and history of schizophrenia and schizotypy (Adriaens 2003; Adriaens, in press) • A contribution to the debate on the evolution and history of homosexuality and same-sex sexuality (De Block & Adriaens 2004; Adriaens & De Block 2006) Evolutionary psychiatry: an introduction

  24. Introduction History Models Philosophy Conclusion 5. Conclusion • A recent discipline with a long history • A myriad of ways to avoid natural selection • A gold mine for philosophers and for philosophy Evolutionary psychiatry: an introduction

  25. Merci! Evolutionary psychiatry: an introduction

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