Schizophrenia: An Evolutionary Perspective

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Schizophrenia An Evolutionary Perspective

• By Tanya Kraus

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Schizophrenia

• ?a psychotic disorder characterized by major
  disturbances in thought, emotion, and behaviour
  disordered thinking in which ideas are not
  logically related, faulty perception and
  attention, flat or inappropriate affect, and
  bizarre disturbances in motor activity. Patients
  with schizophrenia often withdraw from people and
  reality into a fantasy life of delusions and
  hallucinations.

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Positive/Negative Symptoms

• Positive symptoms Involves behaviour that is not
  normally present in most people. (E.g.
  distortions, disorganized speech, hallucinations,
  or delusions.)
• Negative symptoms Involves behavioural deficits
  that are not present in most people. (E.g.
  avolition, alogia, anhedonia, flat affect, and
  asociality.)

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Other Symptoms

• Many patients experience the following as well as
  positive and negative symptoms.
• Catatonia Defined by several motor
  abnormalities, which can include catatonic
  immobility or waxy flexibility
• Inappropriate Affect Emotional responses that
  are out of context

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Heres Where the Evolution Part Becomes Relevant

• Unusual behaviours that strongly resemble
  schizophrenia have dated back to Mesopotamia
• Universally, the prevalence rate of schizophrenia
  is about 1, which exceeds common mutation rates
• There is a strong genetic component (E.g. twin
  and adoption studies)
• Conditions such as schizophrenia have a long
  history and a strong genetic base, meaning
  evolutionary explanations must be acknowledged

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Evolution Perspectives

• Evolutionary perspectives can be divided into two
  groups
• Theories that assume schizophrenia is a
  disadvantageous by-product of human brain
  evolution
• Theories that consider schizophrenia to have an
  evolutionary advantage

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Schizophrenia Disadvantageous By-Product of
Human Brain Evolution

• Theory 1 Farleys argument that schizophrenia
  could be an extreme variant of normal social
  behaviour
• Flaw This theory fails to explain why
  schizophrenia is comprised of both negative and
  positive symptoms

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Disadvantages, Cont.

• Theory 2 Randalls novel neural pathways
  modelbiological trial and error of connection
  would produce a range of behavioural variants,
  including schizophrenia.
• Flaw Denies the specific symptoms that occur in
  any given disorder, as well as the maintenance of
  pathology

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Disadvantages, Cont.

• Theory 3 Saugstads pathophysiological model,
  which connects many frontal lobe disorders (E.g.
  schizophrenia, infantile autism), to delayed
  cerebral maturation. Again, schizophrenia is
  viewed simply as an outlier within the normal
  bounds of variation
• Flaw It would be atypical for nature to produce
  such large numbers of distinct phenotypes with
  reduced fecundity (Ability to produce many
  children)

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Disadvantages, Cont.

• Theory 4 Yeo and the developmental instability
  model of schizophrenia
• Flaw While being a very intriguing theory, it
  lacks any empirical evidence at this point in
  time. It should be considered speculatively

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Schizophrenia as an Evolutionary Advantage

• Schizophrenia paradox The discrepancy between
  high prevalence rate and reduced fecundity
• This doesnt seem very adaptive, does it?
• There must have been some evolutionary advantage
  to having schizophrenia

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Advantageous Theories

• Theory 1 Huxley, Mayr, Osmond, and Hoffer
  published the first model linking schizophrenia
  to evolutionary concepts. (1964) Speculated that
  reduced fecundity was compensated by higher
  resistance to allergens, shock, and infection
• Flaw No substantial evidence supporting this
  theory

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Advantageous, Cont.

• Theory 2 Kellets model suggesting that certain
  characteristics found in schizophrenia may have
  helped mans territorial instincts
• Flaw This theory addresses only a small
  component of schizophrenia, providing no
  evolutionary explanation for psychotic symptoms

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Advantageous, Cont.

• Theory 3 The schizophrenia gene could possibly
  benefit individuals who carry it but do not have
  the disorder
• Karlsson studied a population of schizophrenics
  in Iceland and discovered that first-degree
  relatives were twice as likely to be members of
  creative professions than the general population
• Flaw Providing an accurate association between
  psychiatric conditions and creativity can be
  difficult

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Conclusion

• Although there are many theories regarding the
  origins and possible evolutionary
  advantages/disadvantages of schizophrenia, none
  of them have truly been proven
• Up until the 1960s, studying schizophrenia from
  an evolutionary perspective was unheard of.
  However, this can only add to our understanding
  of this severe disorder and will hopefully one
  day benefit those who suffer from schizophrenia

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The End!